Resumen Cei 61869

FORM CDV (IEC) 2009-01-09 ® Registered trademark of the International Electrotechnical Commission

38/404/CDVCOMMITTEE DRAFT FOR VOTE (CDV)

PROJET DE COMITÉ POUR VOTE (CDV)Project number IEC 61869-2 Ed. 1.0 Numéro de projet

IEC/TC or SC: 38 CEI/CE ou SC:

Secretariat / Secrétariat Italy

Submitted for parallel voting in CENELEC Soumis au vote parallèle au CENELEC

Date of circulation Date de diffusion 2010-10-22

Closing date for voting (Voting mandatory for P-members) Date de clôture du vote (Vote obligatoire pour les membres (P)) 2011-03-25

Also of interest to the following committees Intéresse également les comités suivants TC13, TC85, TC95, TC99

Supersedes document Remplace le document 38/357A/CD – 38/361B/CC

Proposed horizontal standard Norme horizontale suggérée

Other TC/SCs are requested to indicate their interest, if any, in this CDV to the TC/SC secretary Les autres CE/SC sont requis d’indiquer leur intérêt, si nécessaire, dans ce CDV à l’intention du secrétaire du CE/SC Functions concerned Fonctions concernées

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EMC CEM

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Titre : CEI 61869 Ed. 1: TRANSFORMATEURS DE MESURE - Partie 2: Transformateurs de courant

Title : IEC 61869 Ed. 1: INSTRUMENT TRANSFORMERS - Part 2: Current Transformers

Note d'introduction

Introductory note

ATTENTION

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CENELEC, is drawn to the fact that this Committee Draft for Vote (CDV) for an International Standard is submitted for

parallel voting. The CENELEC members are invited to vote through the

CENELEC online voting system.

Copyright © 2010 International Electrotechnical Commission, IEC. All rights reserved. It is permitted to download this electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions. You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without permission in writing from IEC.

®

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1

IEC 61869-2 2

3

INSTRUMENT TRANSFORMERS 4 5

Part 2: Current Transformers 6

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CONTENTS 7

FOREWORD.................................................................................................................... - 10 - 8 INTRODUCTION.............................................................................................................. - 11 - 9 1 Scope........................................................................................................................ - 13 - 10 2 Normative references ................................................................................................ - 13 - 11 3 Definitions ................................................................................................................. - 13 - 12

3.1 General definitions ........................................................................................... - 13 - 13 3.1.1 Instrument transformer ......................................................................... - 13 - 14 3.1.2 Enclosure ............................................................................................. - 13 - 15 3.1.3 Primary terminals ................................................................................. - 13 - 16 3.1.4 Secondary terminals ............................................................................. - 13 - 17 3.1.5 Secondary circuit .................................................................................. - 13 - 18 3.1.6 Section ................................................................................................. - 13 - 19 3.1.200 Current transformer .............................................................................. - 13 - 20 3.1.201 Measuring current transformer.............................................................. - 13 - 21 3.1.202 Protective current transformer .............................................................. - 13 - 22 3.1.203 Class PR protective current transformer ............................................... - 14 - 23 3.1.204 Class PX protective current transformer ............................................... - 14 - 24 3.1.205 Class TPX protective current transformer for transient performance ............ - 14 - 25 3.1.206 Class TPY protective current transformer for transient performance ............ - 14 - 26 3.1.207 Class TPZ protective current transformer for transient performance ............ - 14 - 27 3.1.208 Multi-ratio current transformer .............................................................. - 14 - 28

3.2 Definitions related to dielectric ratings .............................................................. - 15 - 29 3.2.1 Highest voltage for system (Usys) ......................................................... - 15 - 30 3.2.2 Highest voltage for equipment (Um)...................................................... - 15 - 31 3.2.3 Rated insulation level ........................................................................... - 15 - 32 3.2.4 Isolated neutral system......................................................................... - 15 - 33 3.2.5 Resonant earthed system (a system earthed through an arc-34

suppression coil) .................................................................................. - 15 - 35 3.2.6 Earth fault factor ................................................................................... - 15 - 36 3.2.7 Earthed neutral system......................................................................... - 15 - 37 3.2.8 Solidly earthed neutral system.............................................................. - 15 - 38 3.2.9 Impedance earthed neutral system ....................................................... - 15 - 39 3.2.10 Exposed installation ............................................................................. - 15 - 40 3.2.11 Non-exposed installation ...................................................................... - 15 - 41

3.3 Definitions related to current ratings ................................................................. - 15 - 42 3.3.200 Rated primary current (Ipr) ................................................................... - 15 - 43 3.3.201 Rated secondary current (Isr) ............................................................... - 15 - 44 3.3.202 Rated short-time thermal current (Ith) ................................................... - 15 - 45 3.3.203 Rated dynamic current (Idyn)................................................................ - 15 - 46 3.3.204 Rated continuous thermal current (Icth) ................................................ - 15 - 47 3.3.205 Exciting current (Ie) .............................................................................. - 15 - 48

3.4 Definitions related to accuracy ......................................................................... - 16 - 49 3.4.1 Actual transformation ratio (k)............................................................... - 16 - 50 3.4.2 Rated transformation ratio (kr) .............................................................. - 16 - 51 3.4.3 Ratio error (ε) ....................................................................................... - 16 - 52

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3.4.4 Phase displacement (∆φ) ..................................................................... - 16 - 53 3.4.5 Accuracy class ..................................................................................... - 16 - 54 3.4.6 Burden ................................................................................................. - 16 - 55 3.4.7 Rated burden........................................................................................ - 16 - 56 3.4.8 Rated output (Sr) .................................................................................. - 16 - 57 3.4.200 Rated resistive burden (Rb) .................................................................. - 16 - 58 3.4.201 Secondary winding resistance (Rct) ...................................................... - 16 - 59 3.4.202 Composite error (εc).............................................................................. - 16 - 60 3.4.203 Rated instrument limit primary current (IPL) ........................................... - 17 - 61 3.4.204 Instrument security factor (FS) ............................................................. - 17 - 62 3.4.205 Secondary limiting e.m.f for measuring current transformers................. - 17 - 63 3.4.206 Rated accuracy limit primary current (Ialf) ............................................ - 17 - 64 3.4.207 Accuracy limit factor (ALF) ................................................................... - 17 - 65 3.4.208 Secondary limiting e.m.f. for protective current transformers ................ - 17 - 66 3.4.209 Saturation flux (Ψs) .............................................................................. - 17 - 67 3.4.210 Remanent flux (Ψr) ............................................................................... - 17 - 68 3.4.211 Remanence factor (Kr) ......................................................................... - 18 - 69 3.4.212 Rated secondary loop time constant (Ts) .............................................. - 18 - 70 3.4.213 Excitation characteristic........................................................................ - 18 - 71 3.4.214 Rated knee point e.m.f. (Ek) ................................................................. - 18 - 72 3.4.215 Rated turns ratio................................................................................... - 18 - 73 3.4.216 Turns ratio error (εt) ............................................................................. - 18 - 74 3.4.217 Dimensioning factor (Kx) ...................................................................... - 18 - 75 3.4.218 Rated primary short-circuit current (Ipsc)..................................................... - 18 - 76 3.4.219 Instantaneous error current (iε) ................................................................. - 19 - 77

3.4.220 Peak value of total error ( ε ) .................................................................... - 19 - 78

3.4.221 Peak value of alternating error component ( acε ) ........................................ - 19 - 79

3.4.222 Specified duty cycle (C-0 and / or C-0-C-0) ................................................ - 19 - 80 3.4.223 Specified primary time constant (TP) ......................................................... - 20 - 81 3.4.224 Fault duration (t’, t’’)................................................................................ - 20 - 82 3.4.225 Specified time to accuracy limit (t’al , t’’al) ................................................... - 20 - 83 3.4.226 Fault repetition time (tfr) ........................................................................... - 20 - 84 3.4.227 Secondary loop resistance (Rs) ................................................................ - 20 - 85 3.4.228 Rated symmetrical short-circuit current factor (Kssc) .................................... - 21 - 86 3.4.229 Rated transient dimensioning factor (Ktd) ................................................... - 21 - 87 3.4.230 Low leakage reactance current transformer .......................................... - 21 - 88 3.4.231 High leakage reactance current transformer ......................................... - 22 - 89 3.4.232 Rated equivalent limiting secondary voltage (Ual)........................................ - 22 - 90 3.4.233 Peak value of the exciting secondary current at Ual (Îal)........................ - 22 - 91 3.4.234 Factor of construction Fc....................................................................... - 22 - 92

3.5 Definitions related to other ratings .................................................................... - 23 - 93 3.5.1 Rated frequency (fR) ............................................................................. - 23 - 94 3.5.2 Mechanical load (F) .............................................................................. - 23 - 95 3.5.3 Internal arc fault protection instrument transformer .............................. - 23 - 96

3.6 Definitions related to gas insulation .................................................................. - 23 - 97 3.6.1 Pressure relief device ........................................................................... - 23 - 98 3.6.2 Gas-insulated metal-enclosed instrument transformer .......................... - 23 - 99 3.6.3 Closed pressure system ....................................................................... - 23 - 100 3.6.4 Rated filling pressure............................................................................ - 23 - 101

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3.6.5 Minimum functional pressure ................................................................ - 23 - 102 3.6.6 Design pressure of the enclosure ......................................................... - 23 - 103 3.6.7 Design temperature of the enclosure .................................................... - 23 - 104 3.6.8 Absolute leakage rate ........................................................................... - 23 - 105 3.6.9 Relative leakage rate (Frel).................................................................... - 23 - 106

3.7 Index of abbreviations ...................................................................................... - 23 - 107 4 Normal and special service conditions ....................................................................... - 25 - 108

4.1 General ............................................................................................................ - 25 - 109 4.2 Normal service conditions ................................................................................ - 25 - 110

4.2.1 Ambient air temperature ....................................................................... - 25 - 111 4.2.2 Altitude ................................................................................................. - 25 - 112 4.2.3 Vibrations or earth tremors ................................................................... - 25 - 113 4.2.4 Other service conditions for indoor instrument transformers ................. - 25 - 114 4.2.5 Other service conditions for outdoor instrument transformers ............... - 25 - 115

4.3 Special service conditions ................................................................................ - 25 - 116 4.3.1 General ................................................................................................ - 25 - 117 4.3.2 Altitude ................................................................................................. - 25 - 118 4.3.3 Ambient temperature ............................................................................ - 25 - 119 4.3.4 Vibrations or earth tremors ................................................................... - 25 - 120 4.3.5 Earthquakes ......................................................................................... - 25 - 121

4.4 System earthing ............................................................................................... - 25 - 122 5 Ratings...................................................................................................................... - 25 - 123

5.1 General ............................................................................................................ - 25 - 124 5.2 Highest voltage for equipment .......................................................................... - 25 - 125 5.3 Rated insulation levels ..................................................................................... - 25 - 126

5.3.1 General ................................................................................................ - 25 - 127 5.3.2 Rated primary terminal insulation level ................................................. - 25 - 128 5.3.3 Other requirements for primary terminals insulation .............................. - 26 - 129 5.3.4 Between-section insulation requirements .............................................. - 26 - 130 5.3.5 Insulation requirements for secondary terminals ................................... - 26 - 131 5.3.200 Inter-turn insulation requirements ......................................................... - 26 - 132

5.4 Rated frequency ............................................................................................... - 26 - 133 5.5 Rated output .................................................................................................... - 26 - 134 5.6 Rated accuracy class ....................................................................................... - 26 - 135

5.6.200 Measuring current transformers ............................................................ - 26 - 136 5.6.201 Protective current transformers............................................................. - 28 - 137

5.200 Standard values of rated primary current .......................................................... - 32 - 138 5.200.1 Single ratio transformers ...................................................................... - 32 - 139 5.200.2 Multi-ratio transformers ........................................................................ - 33 - 140

5.201 Standard values of rated secondary currents .................................................... - 33 - 141 5.202 Rated continuous thermal current ..................................................................... - 33 - 142 5.203 Short-time current ratings ................................................................................. - 33 - 143

5.203.1 Rated short-time thermal current (Ith) ................................................... - 33 - 144 5.203.2 Rated dynamic current (Idyn)................................................................ - 33 - 145

6 Design and construction ............................................................................................ - 34 - 146 6.1 Requirements for liquids used in equipment ..................................................... - 34 - 147

6.1.1 General ................................................................................................ - 34 - 148 6.1.2 Liquid quality ........................................................................................ - 34 - 149 6.1.3 Liquid level device ................................................................................ - 34 - 150

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6.1.4 Liquid tightness .................................................................................... - 34 - 151 6.2 Requirements for gases used in equipment ...................................................... - 34 - 152

6.2.1 General ................................................................................................ - 34 - 153 6.2.2 Gas quality ........................................................................................... - 34 - 154 6.2.3 Gas monitoring device .......................................................................... - 34 - 155 6.2.4 Gas tightness ....................................................................................... - 34 - 156 6.2.5 Pressure relief device ........................................................................... - 34 - 157

6.3 Requirements for solid materials used in equipment ......................................... - 34 - 158 6.4 Requirements for temperature rise of parts and components ............................ - 34 - 159

6.4.1 General ................................................................................................ - 34 - 160 6.4.2 Influence of altitude on temperature-rise............................................... - 35 - 161

6.5 Requirements for earthing of equipment ........................................................... - 35 - 162 6.5.1 General ................................................................................................ - 35 - 163 6.5.2 Earthing of the enclosure...................................................................... - 35 - 164 6.5.3 Electrical continuity .............................................................................. - 35 - 165

6.6 Requirements for the external insulation........................................................... - 35 - 166 6.6.1 Pollution ............................................................................................... - 35 - 167 6.6.2 Altitude ................................................................................................. - 35 - 168

6.7 Mechanical requirements.................................................................................. - 35 - 169 6.8 Multiple chopped impulse on primary terminals ................................................ - 35 - 170 6.9 Internal arc fault protection requirements ......................................................... - 35 - 171 6.10 Degrees of protection by enclosures................................................................. - 35 - 172

6.10.1 General ................................................................................................ - 35 - 173 6.10.2 Protection of persons against access to hazardous parts and 174

protection of the equipment against ingress of solid foreign objects ...... - 35 - 175 6.10.3 Protection against ingress of water ....................................................... - 35 - 176 6.10.4 Indoor instrument transformers ............................................................. - 35 - 177 6.10.5 Outdoor instrument transformers .......................................................... - 35 - 178 6.10.6 Protection of equipment against mechanical impact under normal 179

service conditions ................................................................................. - 35 - 180 6.11 Electromagnetic Compatibility (EMC) ............................................................... - 35 - 181

6.11.1 General ................................................................................................ - 35 - 182 6.11.2 Requirement for Radio Interference Voltage (RIV) ................................ - 35 - 183 6.11.3 Requirements for immunity ................................................................... - 35 - 184 6.11.4 Requirement for transmitted overvoltages............................................. - 35 - 185

6.12 Corrosion ......................................................................................................... - 35 - 186 6.13 Markings .......................................................................................................... - 35 - 187

6.13.200 Terminal markings – General rules......................................... - 35 - 188 6.13.201 Rating plate markings ............................................................ - 36 - 189 6.13.202 Marking of the rating plate of a measuring current 190

transformer ........................................................................................... - 37 - 191 6.13.203 Marking of the rating plate of a class P protective current 192

transformer ........................................................................................... - 37 - 193 6.13.204 Marking of the rating plate of class PR protective current 194

transformers ......................................................................................... - 37 - 195 6.13.205 Marking of the rating plate of class PX protective current 196

transformers ......................................................................................... - 38 - 197 6.13.206 Marking of the rating plate of current transformers for 198

transient performance........................................................................... - 38 - 199 6.14 Fire hazard....................................................................................................... - 39 - 200

7 Tests ......................................................................................................................... - 39 - 201

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7.1 General ............................................................................................................ - 39 - 202 7.1.1 Classification of tests ........................................................................... - 39 - 203 7.1.2 List of tests........................................................................................... - 39 - 204 7.1.3 Sequence of tests................................................................................. - 40 - 205

7.2 Type tests ........................................................................................................ - 40 - 206 7.2.1 General ................................................................................................ - 40 - 207 7.2.2 Temperature-rise test ........................................................................... - 40 - 208 7.2.3 Impulse voltage withstand test on primary terminals ............................. - 42 - 209 7.2.4 Wet test for outdoor type transformers.................................................. - 43 - 210 7.2.5 Electromagnetic Compatibility (EMC) tests ........................................... - 43 - 211 7.2.6 Test for accuracy.................................................................................. - 43 - 212 7.2.7 Verification of the degree of protection by enclosures ........................... - 47 - 213 7.2.8 Enclosure tightness test at ambient temperature .................................. - 47 - 214 7.2.9 Pressure test for the enclosure ............................................................. - 47 - 215 7.2.200 Short-time current test .......................................................................... - 47 - 216

7.3 Routine tests .................................................................................................... - 48 - 217 7.3.1 Power-frequency voltage withstand tests on primary terminals ............. - 48 - 218 7.3.2 Partial discharge measurement ............................................................ - 48 - 219 7.3.3 Power-frequency voltage withstand tests between sections .................. - 48 - 220 7.3.4 Power-frequency voltage withstand tests on secondary terminals ......... - 48 - 221 7.3.5 Test for accuracy.................................................................................. - 48 - 222 7.3.6 Verification of markings ........................................................................ - 50 - 223 7.3.7 Enclosure tightness test at ambient temperature .................................. - 50 - 224

7.3.7.1 Closed pressure systems for gas ........................................... - 50 - 225 7.3.7.2 Liquid systems ....................................................................... - 50 - 226

7.3.8 Pressure test for the enclosure ............................................................. - 50 - 227 7.3.200 Inter-turn overvoltage test..................................................................... - 50 - 228

7.4 Special tests .................................................................................................... - 51 - 229 7.4.1 Chopped impulse voltage withstand test on primary terminals .............. - 51 - 230 7.4.2 Multiple chopped impulse test on primary terminals .............................. - 51 - 231 7.4.3 Measurement of capacitance and dielectric dissipation factor ............... - 51 - 232 7.4.4 Transmitted overvoltage test ................................................................ - 52 - 233 7.4.5 Mechanical tests................................................................................... - 52 - 234 7.4.6 Internal arc fault test............................................................................. - 52 - 235 7.4.7 Enclosure tightness tests at low and high temperatures ........................ - 52 - 236 7.4.8 Gas Dew point test ............................................................................... - 52 - 237 7.4.9 Corrosion test ....................................................................................... - 52 - 238 7.4.10 Fire hazard test .................................................................................... - 52 - 239

7.5 Sample tests .................................................................................................... - 52 - 240 8 Rules for transport, storage, erection, operation and maintenance ............................ - 52 - 241 9 Safety........................................................................................................................ - 52 - 242 10 Influence of products on the natural environment ...................................................... - 52 - 243 Annex 2A Protective current transformers classes P, PR, PX (Normative) ...................... - 53 - 244 2A.1 Vector diagram ................................................................................................. - 53 - 245 2A.2 Turns correction ............................................................................................... - 53 - 246 2A.3 The error triangle ............................................................................................. - 53 - 247 2A.4 Composite error ............................................................................................... - 54 - 248 2A.5 Direct test for composite error .......................................................................... - 55 - 249

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2A.6 Alternative method for the direct measurement of composite error ................... - 56 - 250 2A.7 Use of composite error ..................................................................................... - 56 - 251 Annex 2B Protective current transformers classes for transient performance 252

(Normative) ............................................................................................................... - 58 - 253 2B.1 Basic theoretical equations for transient dimensioning...................................... - 58 - 254

2B.1.1 Short-circuit .......................................................................................... - 58 - 255 2B.1.2 Transient factor .................................................................................... - 59 - 256 2B.1.3 Duty cycles ........................................................................................... - 64 - 257

2B.2 Determination of the magnetizing characteristic of protective current 258 transformers for transient performance ...................................................................... - 65 - 259 2B.2.1 General ................................................................................................ - 65 - 260 2B.2.2 A.C. method ......................................................................................... - 65 - 261 2B.2.3 D.C. method ......................................................................................... - 66 - 262 2B.2.4 Capacitor discharge method ................................................................. - 68 - 263

2B.3 Determination of the error at limiting conditions of protective current 264 transformers for transient performance ...................................................................... - 69 - 265 2B.3.1 Direct test............................................................................................. - 69 - 266 2B.3.2 Indirect test .......................................................................................... - 70 - 267

2B.4 Alternative measurement of the steady state ratio error .................................... - 72 - 268 Annex 2C Technique used in temperature rise test of oil-immersed transformers to 269

determine the thermal constant by an experimental estimation (informative).............. - 74 - 270 Annex 2D Determination of the turns ratio error (informative)........................................... - 76 - 271 272

273 FIGURES 274

275 Figure 201 - Duty cycles ................................................................................................. - 19 - 276 Figure 202 - Primary time constant Tp .............................................................................. - 20 - 277 Figure 203 - Relevant peaks of magnetic flux for determination of Ktd ............................ - 21 - 278 Figure 2A.1 ...................................................................................................................... - 53 - 279 Figure 2A.2 ...................................................................................................................... - 54 - 280 Figure 2A.3 ...................................................................................................................... - 54 - 281 Figure 2A.4 ...................................................................................................................... - 55 - 282 Figure 2A.5 ...................................................................................................................... - 55 - 283 Figure 2A.6 ...................................................................................................................... - 56 - 284

Fig. 2B.1: Short-circuit current with highest peak (γ = 90°) and lower asymmetry 285 (γ = 140°) ......................................................................................................................... - 58 - 286 Fig. 2B.2: Magnetic-flux for the two cases in Fig. 2B.1 ..................................................... - 59 - 287 Fig. 2B.3: Relevant time ranges for calculation of transient factor .................................... - 59 - 288

Fig. 2B.4 Determination of Ktf for δ = 3° (Ts=61 ms) and f=50 Hz ..................................... - 60 - 289

Fig. 2B.5 Determination of Ktf for δ = 1.5° (Ts=122 ms) and f=50 Hz................................ - 61 - 290

Fig. 2B.6 Determination of Ktf for δ = 0.1° (Ts= 1.8 s) and f=50 Hz .................................. - 61 - 291

Fig. 2B.7 Determination of Ktf for δ = 3° (Ts=50 ms) and f=60 Hz .................................... - 61 - 292

Fig. 2B.8 Determination of Ktf for δ = 1.5° (Ts=100 ms) and f=60 Hz................................ - 62 - 293

Fig. 2B.9 Determination of Ktf for δ = 0.1° (Ts= 1.5 s) and f=60 Hz .................................. - 62 - 294

Fig. 2B.10 Determination of Ktf for δ = 3° (Ts=182 ms) and f=16.7 Hz.............................. - 62 - 295

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Fig. 2B.11 Determination of Ktf for δ = 1.5° (Ts=365 ms) and f=16.7 Hz........................... - 63 - 296

Fig. 2B.12 Determination of Ktf for δ = 0.1° (Ts= 5.5 s) and f=16.7 Hz .............................. - 63 - 297 Fig. 2B.13: Basic circuit ................................................................................................... - 65 - 298 Fig. 2B.14: Determination of remanence factor by hysteresis loop ................................... - 66 - 299 Fig. 2B.15: Circuit for d.c. method.................................................................................... - 67 - 300 Fig. 2B.16: Typical records .............................................................................................. - 67 - 301 Fig. 2B.17: Circuit for capacitor discharge method ........................................................... - 68 - 302 Fig. 2B.19: Measurement of error currents ....................................................................... - 70 - 303 Fig. 2B.20 Simplified equivalent circuit of the current transformer .................................... - 72 - 304 Figure C200.1 - Graphical extrapolation to ultimate temperature rise ............................... - 75 - 305

306

TABLES 307 308

Table 20 1 – Limits of current error and phase displacement for measuring current 309 transformers (classes from 0.1 to 1)................................................................................. - 27 - 310 Table 20 2 – Limits of current error and phase displacement for measuring current 311 transformers for special application ................................................................................. - 28 - 312 Table 20 3 – Limits of current error for measuring current transformers (classes 3 and 313 5) - 28 - 314 Table 20 4 – Definitions of protective classes .................................................................. - 28 - 315 Table 205 – Limits of error for protective current transformers class P and PR ................ - 29 - 316 Table 206 – Error limits for TPX, TPY and TPZ current transformers................................ - 31 - 317 Table 207 – Specification Method for TPX, TPY and TPZ current transformers ................ - 32 - 318 Table 208 – Markings of terminals ................................................................................... - 36 - 319 Table 209 – List of tests................................................................................................... - 39 - 320 Table 210 – Gas type and pressure during type, routine and special tests ....................... - 40 - 321 Table 211 – Additional type tests for protective current transformers for transient 322 performance .................................................................................................................... - 44 - 323

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INTERNATIONAL ELECTROTECHNICAL COMMISSION 324

____________ 325 326


Part 2: Current Transformers 329 330 331

FOREWORD 332

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising 333 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote 334 international co-operation on all questions concerning standardization in the electrical and electronic fields. To 335 this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, 336 Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC 337 Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested 338 in the subject dealt with may participate in this preparatory work. International, governmental and non-339 governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely 340 with the International Organization for Standardization (ISO) in accordance with conditions determined by 341 agreement between the two organizations. 342

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international 343 consensus of opinion on the relevant subjects since each technical committee has representation from all 344 interested IEC National Committees. 345

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National 346 Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC 347 Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any 348 misinterpretation by any end user. 349

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications 350 transparently to the maximum extent possible in their national and regional publications. Any divergence 351 between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in 352 the latter. 353

5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any 354 equipment declared to be in conformity with an IEC Publication. 355

6) All users should ensure that they have the latest edition of this publication. 356 7) No liability shall be attached to IEC or its directors, employees, servants or agents including individual experts 357

and members of its technical committees and IEC National Committees for any personal injury, property 358 damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) 359 and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC 360 Publications. 361

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is 362 essential for the correct application of this publication. 363

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of 364 patent rights. IEC shall not be held responsible for identifying any or all such patent rights. 365

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INTRODUCTION 366

This International Standard IEC 61869-2 has been prepared by subcommittee 38: Instrument 367 transformers. 368

TC 38 decided to restructure the whole set of stand-alone Standards in the IEC 60044-X 369 series and transform it into a new set of standards composed of General Requirements 370 documents and Specific Requirements documents. 371

This Standard is the first issue of Specific Requirements for current transformers and shall be 372 read together with IEC 61869-1 General Requirements for Instrument Transformers 373

This Standard covers all specific requirements formerly found in the 60044-1 and 60044-6 374 standard. Additionally, it introduces some technical innovations: 375

• requirements for gas-insulated instrument transformers 376

• additional special tests 377

• requirements for internal arc fault protection 378

• requirements for degrees of protection by enclosure 379

• requirements for resistance to corrosion 380

• requirements for safety and environmental concerns 381

• standardization and adaptation of the requirements of current transformers for 382 transient performance 383

The text of this standard is based on the following documents: 384

FDIS Report on voting

38/XX/FDIS 38/XX/RVD

385 Full information on the voting for the approval of this standard can be found in the report on 386 voting indicated in the above table. 387

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. 388

This standard is Part 2 of IEC 61869, published under the general title Instrument 389 transformers. 390

This part 2 is to be read in conjunction with, and is based on, IEC 61869-1: “General 391 Requirements” - first edition (2007)- however the reader is encouraged to use its most recent 392 edition. 393

394 This Part 2 follows the structure of IEC 61869-1 and supplements or modifies its 395 corresponding clauses. 396

397 When a particular subclause of Part 1 is not mentioned in this Part 2, that subclause applies. 398 When this standard states “addition”, “modification” or “replacement”, the relevant text in Part 399 1 is to be adapted accordingly. 400

401 For additional clauses, subclauses, figures, tables, annexes or note, the following numbering 402 system is used: 403 – clauses, subclauses, tables and figures that are numbered starting from 201 are additional 404 to those in Part 1; 405 – additional annexes are lettered 2A, 2B, etc. 406 An overview of the planned set of standards at the date of publication of this document is 407 given below: 408

61869-2 ed. 1 © IEC 38/404/CDV - 12 -

PRODUCT FAMILY STANDARDS PRODUCT STANDARD

PRODUCTS OLD STANDARD

61869-2 ADDITIONAL REQUIREMENTS FOR CURRENT TRANSFORMERS

60044-1

61869-3 ADDITIONAL REQUIREMENTS FOR INDUCTIVE VOLTAGE TRANSFORMERS

60044-2

61869-4 ADDITIONAL REQUIREMENTS FOR COMBINED TRANSFORMERS

60044-3

61869-5 ADDITIONAL REQUIREMENTS FOR CAPACITIVE VOLTAGE TRANSFORMERS

60044-5

61869-7 ADDITIONAL REQUIREMENTS FOR ELECTRONIC VOLTAGE TRANSFORMERS

60044-7

61869-8 ADDITIONAL REQUIREMENTS FOR ELECTRONIC CURRENT TRANSFORMERS

61869-9 DIGITAL INTERFACE FOR INSTRUMENT TRANSFORMERS

61869-10 ADDITIONAL REQUIREMENTS FOR LOW-POWER STAND-ALONE CURRENT SENSORS

60044-8

61869-11 ADDITIONAL REQUIREMENTS FOR LOW POWER STAND ALONE VOLTAGE SENSOR

60044-7

61869-12 ADDITIONAL REQUIREMENTS FOR COMBINED ELECTRONIC INSTRUMENT TRANSFORMER OR COMBINED STAND ALONE SENSORS

61869-1

GENERAL REQUIREMENTS FOR INSTRUMENT TRANSFORMERS

61869-6

ADDITIONAL GENERAL REQUIREMENT FOR ELECTRONIC INSTRUMENT TRANSFORMERS AND LOW POWER STAND ALONE SENSORS

61869-13 STAND ALONE MERGING UNIT

The updated list of standards issued by IEC TC38 is available at the website: www.iec.ch 409

The committee has decided that the contents of this publication will remain unchanged until 410 2011-12. At this date, the publication will be 411

• reconfirmed, 412 • withdrawn, 413 • replaced by a revised edition, or 414 • amended. 415

Additionally, an application guide (IEC 61869...) for protection current transformers is under 416 preparation, to give information about 417

• theoretical background of the calculations for current transformers for transient 418 performance 419

• the choose of the specific protection classes depending on the application 420 • the relations between the different class types 421

61869-2 ed. 1 © IEC 38/404/CDV - 13 -


Part 2: Current Transformers 424 425 426

1 Scope 427

This International Standard is applicable to newly manufactured magnetic current 428 transformers for use with electrical measuring instruments or/and electrical protective devices 429 having rated frequencies from 15 Hz to 100 Hz 430

2 Normative references 431

The following referenced documents are essential for the application of this document. For dated 432 references, only the edition cited applies. For undated references, the latest edition of the 433 referenced document (including any amendments) applies. 434 435 IEC 61869-1: General Requirements for Instrument Transformers, including the references 436 mentioned in Clause 2 of IEC 61869-1 437 438

3 Definitions 439

This clause of IEC 61869-1 is applicable with the addition of specific definitions 440

3.1 General definitions 441

3.1.1 Instrument transformer 442

3.1.2 Enclosure 443

3.1.3 Primary terminals 444

3.1.4 Secondary terminals 445

3.1.5 Secondary circuit 446

3.1.6 Section 447

3.1.200 Current transformer 448

An instrument transformer in which the secondary current, in normal conditions of use, is sub-449 stantially proportional to the primary current and differs in phase from it by an angle which is 450 approximately zero for an appropriate direction of the connections. [IEV 321-02-01] 451

3.1.201 Measuring current transformer 452

A current transformer intended to supply an information signal to measuring instruments and 453 meters. (IEV321-02-18) 454

3.1.202 Protective current transformer 455

A current transformer intended to transmit an information signal to protective and control 456 devices (IEV321-02-19) 457

61869-2 ed. 1 © IEC 38/404/CDV - 14 -

3.1.203 Class PR protective current transformer 458

A current transformer with limited remanence factor for which, in some cases, a value of the 459 secondary loop time constant and/or a limiting value of the winding resistance may also be 460 specified 461

3.1.204 Class PX protective current transformer 462

A transformer of low leakage reactance for which knowledge of the transformer secondary 463 excitation characteristic, secondary winding resistance, secondary burden resistance and 464 turns ratio is sufficient to assess its performance in relation to the protective relay system with 465 which it is to be used. 466

3.1.205 Class TPX protective current transformer for transient performance 467

Accuracy limit defined by peak value of total error ( ε ) during specified transient duty cycle. 468 No limit for remanent flux. 469 470 471

3.1.206 Class TPY protective current transformer for transient performance 472

Accuracy limit defined by peak value of total error ( ε ) during specified transient duty cycle. 473 The remanent flux is limited. 474 475 476

3.1.207 Class TPZ protective current transformer for transient performance 477

Accuracy limit defined by peak value of alternating error component ( acε ) during specified transient 478 duty cycle. 479

- Specified secondary phase displacement at Ipr 480

- No requirement concerning instantaneous error current iε 481

- Remanent flux to be practically negligible 482 483

3.1.208 Multi-ratio current transformer 484

Current transformer on which more ratios are obtained by connecting the primary winding 485 sections in series or parallel or by means of taps on the secondary winding 486

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3.2 Definitions related to dielectric ratings 487

3.2.1 Highest voltage for system (Usys) 488

3.2.2 Highest voltage for equipment (Um) 489

3.2.3 Rated insulation level 490

3.2.4 Isolated neutral system 491

3.2.5 Resonant earthed system (a system earthed through an arc-suppression 492 coil) 493

3.2.6 Earth fault factor 494

3.2.7 Earthed neutral system 495

3.2.8 Solidly earthed neutral system 496

3.2.9 Impedance earthed neutral system 497

3.2.10 Exposed installation 498

3.2.11 Non-exposed installation 499

3.3 Definitions related to current ratings 500

3.3.200 Rated primary current (Ipr) 501

The value of the primary current on which the performance of the transformer is based 502

[IEV 321-01-11 modified] 503

3.3.201 Rated secondary current (Isr) 504

The value of the secondary current on which the performance of the transformer is based 505

[IEV 321-01-15 modified] 506

3.3.202 Rated short-time thermal current (Ith) 507

The r.m.s. value of the primary current which a transformer will withstand for one second 508 without suffering harmful effects, the secondary winding being short-circuited 509

3.3.203 Rated dynamic current (Idyn) 510

The peak value of the primary current which a transformer will withstand, without being 511 damaged electrically or mechanically by the resulting electromagnetic forces, the secondary 512 winding being short-circuited 513

3.3.204 Rated continuous thermal current (Icth) 514

The value of the current which can be permitted to flow continuously in the primary winding, 515 the secondary winding being connected to the rated burden, without the temperature rise 516 exceeding the values specified. 517

Note: If a current transformer is equipped with cores having different ratios (e.g. 1200/5 and 4000/1), 518 Icth shall be stated as an uniform absolute value, applicable for all cores (e.g. “Icth 1440 A”) 519 520

3.3.205 Exciting current (Ie) 521

The r.m.s. value of the current taken by the secondary winding of a current transformer, when 522 a sinusoidal voltage of rated frequency is applied to the secondary terminals, the primary and 523 any other windings being open-circuited 524

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3.4 Definitions related to accuracy 525

3.4.1 Actual transformation ratio (k) 526

3.4.2 Rated transformation ratio (kr) 527

3.4.3 Ratio error (ε) 528

Clause § 3.4.3 of IEC 61869-1 is applicable with the addition of the following: 529 The ratio error (current error) expressed in per cent is given by the formula: 530

%100)(

p

ps ⋅−

=I

IIkrε 531

where 532

kr is the rated transformation ratio; 533

Ip is the actual primary current; 534

Is is the actual secondary current when Ip is flowing, under the conditions of measurement 535

536

3.4.4 Phase displacement (∆φ) 537

3.4.5 Accuracy class 538

3.4.6 Burden 539

3.4.7 Rated burden 540

3.4.8 Rated output (Sr) 541

3.4.200 Rated resistive burden (Rb) 542

Rated value of the secondary connected resistive burden in ohms 543

3.4.201 Secondary winding resistance (Rct) 544

Secondary winding d.c. resistance in ohms corrected to 75 ºC or such other temperature as 545 may be specified. 546

NOTE: The actual winding resistance Rct will be ≤ a possibly defined upper limit. 547

3.4.202 Composite error* (εc) 548

Under steady-state conditions, the r.m.s. value of the difference between: 549

a) the instantaneous values of the primary current, and 550 b) the instantaneous values of the actual secondary current multiplied by the rated 551

transformation ratio, the positive signs of the primary and secondary currents corres-552 ponding to the convention for terminal markings. 553

The composite error εc is generally expressed as a percentage of the r.m.s. values of the 554 primary current according to the formula: 555

∫ −=T

tiikTI 0

2psr

pc d)(1100ε 556

where 557 kr is the rated transformation ratio; 558 Ip is the r.m.s. value of the primary current; 559 ————————— * See annexe 2A.

61869-2 ed. 1 © IEC 38/404/CDV - 17 -

ip is the instantaneous value of the primary current; 560

is is the instantaneous value of the secondary current; 561

T is the duration of one cycle. 562

3.4.203 Rated instrument limit primary current (IPL) 563

The value of the minimum primary current at which the composite error of the measuring 564 current transformer is equal to or greater than 10 %, the secondary burden being equal to the 565 rated burden 566

NOTE The composite error should be greater than 10 %, in order to protect the apparatus supplied by the 567 instrument transformer against the high currents produced in the event of system fault. 568

3.4.204 Instrument security factor (FS) 569

The ratio of rated instrument limit primary current to the rated primary current 570

NOTE 1 Attention should be paid to the fact that the actual instrument security factor is affected by the burden. 571 As burden value is significantly lower than rated one, larger current values will be produced on the secondary side 572 in case of short circuit current. 573

NOTE 2 In the event of system fault currents flowing through the primary winding of a current transformer, the 574 safety of the apparatus supplied by the transformer is greatest when the value of the rated instrument security 575 factor (FS) is small. 576

3.4.205 Secondary limiting e.m.f for measuring current transformers 577

The product of the instrument security factor FS, the rated secondary current and the vectorial 578 sum of the rated burden and the impedance of the secondary winding 579

NOTE 1 The method by which the secondary limiting e.m.f. is calculated will give a higher value than the real one. 580 It was chosen in order to apply the same test method as in 7.3.5.201 and 7.2.6.201 for protective current 581 transformers. 582

Other methods may be used by agreement between manufacturer and purchaser. 583

NOTE 2 For calculating the secondary limiting e.m.f., the secondary winding resistance should be corrected to a 584 temperature of 75 °C. 585

3.4.206 Rated accuracy limit primary current (Ialf) 586

The value of primary current up to which the transformer will comply with the requirements for 587 composite error 588

3.4.207 Accuracy limit factor (ALF) 589

The ratio of the rated accuracy limit primary current to the rated primary current 590

3.4.208 Secondary limiting e.m.f. for protective current transformers 591

The product of the accuracy limit factor, the rated secondary current and the vectorial sum of 592 the rated burden and the impedance of the secondary winding 593

3.4.209 Saturation flux (Ψs) 594

That peak value of the flux which would exist in a core in the transition from the non-saturated 595 to the fully saturated condition and deemed to be that point on the transient Ψ-ie characteristic 596 for the core concerned at which a 10 % increase in Ψ causes ie to be increased by 50 % 597

598

3.4.210 Remanent flux (Ψr) 599

That value of flux which would remain in the core 3 min after the interruption of an exciting 600 current of sufficient magnitude to induce the saturation flux (Ψs) 601

61869-2 ed. 1 © IEC 38/404/CDV - 18 -

3.4.211 Remanence factor (Kr) 602

The ratio Kr = Ψr /Ψs, expressed as a percentage (%) 603

3.4.212 Rated secondary loop time constant (Ts) 604

Value of the time constant of the secondary loop of the current transformer obtained from the 605 sum of the magnetizing and the leakage inductance (Ls) and the secondary loop resistance 606 (Rs) 607

Ts = Ls / Rs 608

3.4.213 Excitation characteristic 609

A graphical or tabular presentation of the relationship between the r.m.s. value of the exciting 610 current and a sinusoidal r.m.s. e.m.f. applied to the secondary terminals of a current 611 transformer, the primary and other windings being open-circuited, over a range of values 612 sufficient to define the characteristics from low levels of excitation up to1.1 the rated knee 613 point e.m.f. 614

3.4.214 Rated knee point e.m.f. (Ek) 615

That minimum sinusoidal e.m.f. (r.m.s.) at rated power frequency when applied to the 616 secondary terminals of the transformer, all other terminals being open-circuited, which when 617 increased by 10 % causes the r.m.s. exciting current to increase by no more than 50 % 618

NOTE: The actual knee point e.m.f. will be ≥ the rated knee point e.m.f. 619

620

3.4.215 Rated turns ratio 621

The required ratio of the number of primary turns to the number of secondary turns 622

EXAMPLE 1 1/600 (one primary turn with six hundred secondary turns) 623 EXAMPLE 2 2/600 (two primary turn with six hundred secondary turns). 624

3.4.216 Turns ratio error (εt) 625

The difference between the rated and actual turns ratios, expressed as a percentage 626

100%ratioturnsrated

ratio)turnsratedratioturns(actual×

−=tε 627

3.4.217 Dimensioning factor (Kx) 628

A factor assigned by the purchaser to indicate the multiple of rated secondary current (Isn) 629 occurring under power system fault conditions, inclusive of safety factors, up to which the 630 transformer is required to meet performance requirements. 631 632

3.4.218 Rated primary short-circuit current (Ipsc) 633

The r.m.s. value of primary symmetrical short-circuit current on which the rated accuracy performance 634 of the current transformer is based. (While ith concerns the thermal limit, Ipsc is related to the accuracy 635 limit.) 636

NOTE: Usually, Ipsc will be smaller than ith. 637

638

61869-2 ed. 1 © IEC 38/404/CDV - 19 -

3.4.219 Instantaneous error current (iε) 639

Difference between the instantaneous values of the secondary current (is) multiplied by (kr), and the 640 primary current (ip): 641 642

psr i - i k i ⋅=ε 643 644 645

When both alternating current components (isac , ipac) and direct current components (isdc , ipdc) are 646 present, the constituent components (iεac , iεdc) are separately identified as follows: 647 648

)i - i (k )i - i (k i i i pdcsdcrpacsacr ⋅+⋅=+= dcac εεε 649 650

3.4.220 Peak value of total error ( ε ) 651

Maximum value (îε) of instantaneous error current (see 3.4.219) for the specified duty cycle, expressed 652 as a percentage of the peak value of the rated primary short-circuit current: 653 654

655

%1002

ˆˆ ⋅

⋅=

pscIiεε 656

657

3.4.221 Peak value of alternating error component ( acε ) 658

Maximum value aciε of the alternating current component (see 3.4.219), expressed as a percentage of 659 the peak value of the rated primary short-circuit current 660 661

%1002

ˆˆ ⋅

⋅=

psc

acac I

iεε 662

663

3.4.222 Specified duty cycle (C-0 and / or C-0-C-0) 664

Duty cycle in which during each specified energization, the primary energizing current is assumed to 665 have a DC offset. 666 667

668 C-O C-O-C-O 669 670

Figure 201 - Duty cycles 671

672 673

61869-2 ed. 1 © IEC 38/404/CDV - 20 -

3.4.223 Specified primary time constant (TP) 674

That specified value of the time constant of the d.c. component of the primary short circuit current on 675 which the performance of the current transformer is based. 676 677 678

679 680

Figure 202 - Primary time constant Tp 681

682

3.4.224 Fault duration (t’, t’’) 683

t’: duration of first fault 684 t’’: duration of second fault (if any) 685 686 See figure 201 687 688

3.4.225 Specified time to accuracy limit (t’al , t’’al) 689

Time during which the specified accuracy is maintained. t’al is used for the first energization, t’’al for 690 the second energization (if any). See figure 201 691 692 NOTE - This time will usually be defined by the critical measuring time of the associated protection scheme. 693 For determination of the magnetic core flux, it is necessary to consider the total fault duration. 694

3.4.226 Fault repetition time (tfr) 695

Time interval between interruption and re-application of the primary short-circuit current during a circuit 696 breaker auto-reclosing duty cycle in case of a non-successful fault clearance. See figure 201 697

3.4.227 Secondary loop resistance (Rs) 698

Total resistance of the secondary circuit 699 700

ctbs RR R += 701

61869-2 ed. 1 © IEC 38/404/CDV - 21 -

702

3.4.228 Rated symmetrical short-circuit current factor (Kssc) 703

704

The ratio: pr

pscssc I

I K = 705

3.4.229 Rated transient dimensioning factor (Ktd) 706

The ratio Ψa / Ψs , where 707 708 Ψa is the peak value of the total magnetic flux of the asymmetrical primary current within the relevant 709 time interval1 at rated burden. 710 711 Ψs is the peak value of the steady state a.c. flux of the appropriate symmetrical primary current at 712 rated burden. See figure 203. 713 714 Note 1: 715 The worst case inception angle of the asymmetric primary short circuit current which leads to the highest possible peak of the 716 magnetic flux shall be considered. See annex B.1. The possibility for reduction of the asymmetry by restricting the current 717 inception angle will be discussed in the application guide. 718

719 Figure 203 - Relevant peaks of magnetic flux for determination of Ktd 720

721

3.4.230 Low leakage reactance current transformer 722

Current transformer for which a knowledge of the secondary excitation characteristic and secondary 723 winding resistance is sufficient for an assessment of its transient performance for any combination of 724 primary current and burden. 725 726

61869-2 ed. 1 © IEC 38/404/CDV - 22 -

3.4.231 High leakage reactance current transformer 727

Current transformer which does not satisfy the requirements of 3.4.230, and for which an additional 728 allowance is made by the manufacturer to take account of influencing effects which result in additional 729 leakage flux. 730 731

3.4.232 Rated equivalent limiting secondary voltage (Ual) 732

That r.m.s. value of the equivalent secondary circuit voltage at rated frequency necessary to satisfy 733 the specified duty cycle: 734

srbcttdsscal IRRKKU ⋅+⋅⋅= )( 735

736

3.4.233 Peak value of the exciting secondary current at Ual (Îal) 737

738

3.4.234 Factor of construction Fc 739

The factor of construction Fc reflects the possible differences in measuring results at limiting 740 conditions between direct test and indirect test methods. Fc is based on magnetic flux 741 measurements: 742 743

dir

indcF

ΨΨ

= 744

745 where 746 747

dirΨ is the magnetic flux corresponding to error limiting conditions, measured in a direct test. 748 The corresponding instantaneous error current Iεd shall also be determined. 749 750

indΨ is the magnetic flux measured in an indirect test, determined for the above mentioned 751 magnetizing current Iεd . 752 753 The measuring procedure is given in annex B.3.3.4 754 755

61869-2 ed. 1 © IEC 38/404/CDV - 23 -

3.5 Definitions related to other ratings 756

3.5.1 Rated frequency (fR) 757

3.5.2 Mechanical load (F) 758

3.5.3 Internal arc fault protection instrument transformer 759

3.6 Definitions related to gas insulation 760

3.6.1 Pressure relief device 761

3.6.2 Gas-insulated metal-enclosed instrument transformer 762

3.6.3 Closed pressure system 763

3.6.4 Rated filling pressure 764

3.6.5 Minimum functional pressure 765

3.6.6 Design pressure of the enclosure 766

3.6.7 Design temperature of the enclosure 767

3.6.8 Absolute leakage rate 768

3.6.9 Relative leakage rate (Frel) 769

3.7 Index of abbreviations 770

771

IT Instrument Transformer

CT Current Transformer

Usys Highest voltage for system

Um Highest voltage for equipment

Ipr Rated primary current

Isr Rated secondary current

Ith Rated short-time thermal current

Idyn Rated dynamic current

Icth Rated continuous thermal current

Ie Exciting current

k Actual transformation ratio

kr Rated transformation ratio

ε Ratio error

∆φ Phase displacement

Sr Rated output

61869-2 ed. 1 © IEC 38/404/CDV - 24 -

Rb Rated resistive burden

Rct Secondary winding resistance

εc Composite error

IPL Rated instrument limit primary current

FS Instrument security factor

Ialf Rated accuracy limit primary current

ALF Accuracy limit factor

Ψs Saturation flux

Ψr Remanent flux

Kr Remanence factor

Ts Rated secondary loop time constant

Ek Rated knee point e.m.f.

εt Turns ratio error

Kx Dimensioning factor

fR Rated frequency

F Mechanical load

Frel Relative leakage rate

Îal Peak value of the exciting secondary current at Ual

Ipsc Rated primary short-circuit current

iε Instantaneous error current

Kssc Rated symmetrical short-circuit current factor

Ktd Rated transient dimensioning factor

t’ Duration of first fault

t’’ Duration of second fault

t’al Permissible time to accuracy limit in the first fault

t’’al Permissible time to accuracy limit in the second fault

tfr Fault repetition time

Tp Specified primary time constant

Ual Rated equivalent limiting secondary voltage

61869-2 ed. 1 © IEC 38/404/CDV - 25 -

ε Peak value of total error

acε Peak value of alternating error component

772 773

774

4 Normal and special service conditions 775

4.1 General 776

4.2 Normal service conditions 777

4.2.1 Ambient air temperature 778

4.2.2 Altitude 779

4.2.3 Vibrations or earth tremors 780

4.2.4 Other service conditions for indoor instrument transformers 781

4.2.5 Other service conditions for outdoor instrument transformers 782

4.3 Special service conditions 783

4.3.1 General 784

4.3.2 Altitude 785

4.3.2.1 Influence of altitude on external insulation 786

4.3.2.2 Influence of altitude on temperature-rise 787

4.3.3 Ambient temperature 788

4.3.4 Vibrations or earth tremors 789

4.3.5 Earthquakes 790

4.4 System earthing 791

5 Ratings 792

5.1 General 793

5.2 Highest voltage for equipment 794

5.3 Rated insulation levels 795

5.3.1 General 796

5.3.2 Rated primary terminal insulation level 797

Clause 5.3.2 of IEC 61869-1 is applicable with the addition of the following: 798 For a current transformer without primary winding and without primary insulation of its own, 799 the value Um = 0,72 kV is assumed. 800

61869-2 ed. 1 © IEC 38/404/CDV - 26 -

5.3.3 Other requirements for primary terminals insulation 801

5.3.3.1 Partial discharges 802

5.3.3.2 Chopped lightning impulse 803

5.3.3.3 Capacitance and dielectric dissipation factor 804

5.3.4 Between-section insulation requirements 805

5.3.5 Insulation requirements for secondary terminals 806

Clause 5.3.5 of IEC 61869-1 is applicable with the addition of the following: 807

The secondary winding insulation of class PX current transformers having a rated knee point 808 e.m.f. Ek ≥ 2 kV shall be capable of withstanding a rated power frequency withstand voltage of 809 5 kV r.m.s. for 60 s. 810

5.3.200 Inter-turn insulation requirements 811

The rated withstand voltage for inter-turn insulation shall be 4,5 kV peak. 812

For class PX transformers having a rated knee point e.m.f. of greater than 450 V, the rated 813 withstand voltage for the inter-turn insulation shall be a peak voltage of 10 times the r.m.s. 814 value of the specified knee point e.m.f., or 10 kV peak, whichever is the lower. 815

NOTE 1 Due to the test procedure, the wave shape may be highly distorted. 816

5.4 Rated frequency 817

5.5 Rated output 818

The standard values of rated output up to 30 VA are: 819

2,5 – 5,0 – 10 – 15 and 30 VA. 820

Values above 30 VA may be selected to suit the application. 821

NOTE For a given transformer, provided one of the values of rated output is standard and associated with a 822 standard accuracy class, the declaration of other rated outputs, which may be non-standard values, but associated 823 with other standard accuracy classes, is not precluded. 824 825

5.6 Rated accuracy class 826

5.6.200 Measuring current transformers 827

5.6.200.1 Accuracy class designation for measuring current transformers 828

For measuring current transformers, the accuracy class is designated by the highest permissible 829 percentage current error at rated current prescribed for the accuracy class concerned. 830

5.6.200.2 Standard accuracy classes 831

The standard accuracy classes for measuring current transformers are: 832

0,1 - 0,2 – 0,2S –0,5 - 0,5S – 1 – 3 – 5 833

61869-2 ed. 1 © IEC 38/404/CDV - 27 -

5.6.200.3 Limits of current error and phase displacement for measuring 834 current 835 transformers 836

For classes 0.1 – 0.2 – 0.5 and 1, the current error and phase displacement at rated 837 frequency shall not exceed the values given in Table 201 when the secondary burden is any 838 value from 25 % to 100 % of the rated burden. 839

For classes 0.2 S and 0.5 S the current error and phase displacement at the rated frequency 840 shall not exceed the values given in Table 202 when the secondary burden is any value from 841 25 % and 100 % of the rated burden. 842

For class 3 and class 5, the current error at rated frequency shall not exceed the values given 843 in Table 203 when the secondary burden is any value from 50 % to 100 % of the rated 844 burden. 845

The secondary rated burden used for test purposes shall have a power-factor of 0,8 lagging 846 except that when the burden is less than 5 VA, a power-factor of 1,0 shall be used. In no case 847 shall the test burden be less than 1 VA. 848

For current transformers having a rated burden not exceeding 15 VA, an extended range of 849 burden can be specified. The current error and phase displacement shall not exceed the 850 values given in tables 200.1 and 200.2, when the secondary burden is any value from 1 VA to 851 100 % of the rated burden. In this case the power factor shall be 1.0 852

NOTE 1 For current transformers with a rated secondary current of 1A, a range limit lower than 1 VA may be 853 agreed. 854

NOTE 2 At the moment, there is not sufficient experience about the possibility to perform the accuracy 855 measurements at lower current values (test equipment and uncertainty of the obtained results). 856

NOTE 3 In general the prescribed limits of current error and phase displacement are valid for any given position 857 of an external conductor spaced at a distance in air not less than that required for insulation in air at the highest 858 voltage for equipment (Um). 859

Special conditions of application, including lower ranges of operation voltages associated with high current values, 860 should be a matter of separate agreement between manufacturer and purchaser. 861

For multi-ratio transformers with tappings on the secondary winding, the accuracy require-862 ments refer to the highest transformation ratio, unless otherwise specified. 863

When the requirements refer to highest transformation ratio, the manufacturer shall give 864 information about the accuracy class and the rated burden for the other tappings. 865

Table 201 – Limits of current error and phase displacement for 866 measuring current transformers (classes from 0.1 to 1) 867

868

Accuracy class

± Percentage current (ratio) error at percentage of rated

current shown below

± Phase displacement at percentage of rated current shown below

Minutes Centiradians

5 20 100 120 5 20 100 120 5 20 100 120

0.1 0.2 0.5 1

0,4 0,75 1,5 3,0

0,2 0,35 0,75 1,5

0,1 0,2 0,5 1,0

0,1 0,2 0,5 1,0

15 30 90

180

8 15 45 90

5 10 30 60

5 10 30 60

0,45 0,9 2,7 5,4

0,24 0,45 1,35 2,7

0,15 0,3 0,9 1,8

0,15 0,3 0,9 1,8

869

61869-2 ed. 1 © IEC 38/404/CDV - 28 -

Table 202 – Limits of current error and phase displacement for 870 measuring current transformers for special application 871

Accuracy class

± Percentage current (ratio) error at percentage of rated

current shown below

± Phase displacement at percentage of rated current shown below

Minutes Centiradians

1 5 20 100 120 1 5 20 100 120 1 5 20 100 120

0.2 S 0.5 S

0,75 1,5

0,350,75

0,2 0,5

0,2 0,5

0,2 0,5

30 90

15 45

10 30

10 30

10 30

0,9 2,7

0,45 1,35

0,3 0,9

0,3 0,9

0,3 0,9

872 873 874 875

Table 203 – Limits of current error for measuring 876 current transformers (classes 3 and 5) 877

Class ± Percentage current (ratio) error at percentage of rated current shown below

50 120

3

5

3

5

3

5

878

Limits of phase displacement are not specified for class 3 and class 5. 879 880

5.6.200.4 Extended current ratings 881

Current transformers of accuracy classes 0.1 to 1 may be marked as having an extended 882 current rating provided they comply with the following two requirements: 883

a) the rated continuous thermal current shall be the rated extended primary current 884 expressed as a percentage of the rated primary current; 885

b) the limits of current error and phase displacement prescribed for 120 % of rated primary 886 current in Table 201 shall be retained up to the rated extended primary current. 887

5.6.201 Protective current transformers 888

889 Three different approaches are designated to define protective current transformers. In 890 practice, each of the three definitions may result in the same physical realization. For 891 relations between the class definitions, refer to the application guide. 892 893

Table 204 – Definitions of protective classes 894 895

Designation Limit for remanent flux

Explanation

P PR

no 1 yes

Defining a current transformer to meet the requirements of a short circuit current under symmetrical steady state condition, (eventually overdimensioning it in order to make it suitable for asymmetrical short circuit current)

PX

no 1

Defining a current transformer by requiring its magnetizing characteristic.

61869-2 ed. 1 © IEC 38/404/CDV - 29 -

TPX TPY

TPZ

no 1 yes

yes

Defining a current transformer to meet the requirements of an asymmetrical short circuit current

896

Note 1: Although there is no limit of remanent flux, air gaps are allowed, e.g. in split core current transformers. 897

898

5.6.201.1 Class P protective transformers 899

5.6.201.1.1 Standard accuracy limit factors 900

The standard accuracy limit factors are: 901

5 – 10 – 15 – 20 – 30 902

5.6.201.1.2 Accuracy class designation 903

For protective current transformers, the accuracy class is designed by the highest permissible 904 percentage composite error at the rated accuracy limit primary current prescribed for the 905 accuracy class concerned, followed by the letter “P” (meaning protection). 906

5.6.201.1.3 Standard accuracy classes 907

The standard accuracy classes for protective current transformers are: 908

5P and 10P 909

5.6.201.1.4 Limits of errors for protective current transformers 910

At rated frequency and with rated burden connected, the current error, phase displacement 911 and composite error shall not exceed the values given in Table 205. 912

For testing purposes when determining current error and phase displacement, the burden 913 shall have a power-factor of 0,8 inductive except that, where the burden is less than 5 VA, a 914 power-factor of 1,0 is permissible. 915

For the determination of composite error, the burden shall have a power-factor of between 0,8 916 inductive and unity at the discretion of the manufacturer. 917

Table 205 – Limits of error for protective current transformers class P and PR 918 919

Accuracy class Current error at ratedprimary current

%

Phase displacement at rated primary current

Composite error at rated accuracy limit primary

current %

minutes centiradians

5P

10P

±1

±3

±60

–

±1,8

–

5

10

920

921

61869-2 ed. 1 © IEC 38/404/CDV - 30 -

5.6.201.2 Class PR protective current transformers 922

5.6.201.2.1 Standard accuracy limit factors 923

The standard accuracy limit factors are: 924

5 – 10 – 15 – 20 – 30 925

5.6.201.2.2 Accuracy class designation 926

The accuracy class is designated by the highest permissible percentage composite error at 927 the rated accuracy limit primary current prescribed for the accuracy class concerned, followed 928 by the letters "PR" (indicating protection low remanence). 929

5.6.201.2.3 Standard accuracy classes 930

The standard accuracy classes for low remanence protective current transformers are: 931

5 PR and 10 PR 932

5.6.201.2.4 Limits of error for class PR protective current transformers 933

At rated frequency and with rated burden connected, the current error, phase displacement 934 and composite error shall not exceed the values given in Table 205. 935

For testing purposes when determining current error and phase displacement, the burden 936 shall have a power-factor of 0,8 inductive except that, where the burden is less than 5 VA, a 937 power-factor of 1,0 is permissible. 938

For the determination of composite error, the burden shall have a power-factor of between 0,8 939 inductive and unity at the discretion of the manufacturer. 940

5.6.201.2.5 Remanence factor (Kr) 941

The remanence factor (Kr) shall not exceed 10 %. 942

NOTE Insertion of one or more air gaps in the core may be a method for limiting the remanence factor. 943

5.6.201.2.6 Secondary loop time constant (Ts) 944

If required, the value shall be specified by the purchaser. 945

5.6.201.2.7 Secondary winding resistance (Rct) 946

If required, the maximum value shall be agreed between manufacturer and purchaser. 947

5.6.201.3 Class PX protective current transformers 948

The performance of class PX current transformers shall be specified in terms of the following: 949

a) rated primary current (Ipr); 950 b) rated secondary current (Isr); 951

c) rated turns ratio. The turns ratio error shall not exceed ±0,25 %; 952 d) rated knee point e.m.f. (Ek); 953 e) maximum exciting current (Ie) at the rated knee point e.m.f. and/or at a stated percentage 954

thereof; 955 f) maximum value of secondary winding resistance (Rct); 956

61869-2 ed. 1 © IEC 38/404/CDV - 31 -

g) rated resistive burden (Rb); 957 h) dimensioning factor (Kx). 958

NOTE The rated knee point e.m.f. is generally determined as follows: 959

( ) srbctxk IRRKE ×+= ⋅ 960

961

5.6.201.4 Protective current transformers for transient performance 962

5.6.201.4.1 Standard values of rated resistive burden (Rb) 963

Standard values of rated resistive burden in ohms for class TPX, TPY and TPZ current 964 transformers are: 965 966

0.5 – 1 – 2 – 5 Ohm 967 968 The preferred values are underlined. The values are based on a rated secondary current of 969 1A. For current transformers having a rated secondary current other than 1 A, the above 970 values shall be adjusted in inverse ratio to the square of the current. 971 972

5.6.201.4.2 Error limits for TPX, TPY and TPZ current transformers 973

The errors shall not exceed the values given in Error! Reference source not found.6. 974 975 976

Table 206 – Error limits for TPX, TPY and TPZ current transformers 977

978

Class At rated primary current At accuracy limit condition

Ratio error [%] Phase displacement(2)

% Min Centirad

TPX ±1.0 ±60 ±1.8 10ˆ =ε %

TPY ±1.0 ±60 ±1.8 10ˆ =ε % (3)

TPZ ±1.0 180 ±18 5.3±0.6 10ˆ =acε %

NOTE 1 – all error limits shall be observed at Rct, which is defined at 75°C. NOTE 2 - The absolute value of the phase displacement may in some cases be of less importance than achieving minimal deviation from the average value of a given production series. NOTE 3 - Since the total permissible error limit is 10 %, the transient dimensioning factor shall be considered conjunctively with the secondary circuit time constant:

%100ˆ ⋅⋅

=s

td

TK

ωε

979

61869-2 ed. 1 © IEC 38/404/CDV - 32 -

5.6.201.4.3 Limits for remanence factor (Kr) 980

TPX: no limit 981 TPY: %10≤rK 982

TPZ: %10≤rK (given by the design. In practice, Kr << 10%) 983 Therefore, the remanent flux can be neglected. 984 985

5.6.201.4.4 Specification Methods 986

The two specification methods are illustrated in Table 207. 987 In some cases, the definition of one specific duty cycle cannot describe all protection 988 requirements. Therefore, the alternative definition offers the possibility to specify “overall 989 requirements”, which cover the requirements of different duty cycles. 990 991 The specifications shall not be mixed, otherwise the current transformer may be over-992 determined. 993 994 995

Table 207 – Specification Method for TPX, TPY and TPZ current transformers 996

997

Standard specification Alternative specification

CT class designation (TPX, TPY, or TPZ)

CT class designation (TPX, TPY, or TPZ)

Ratio to which the specification applies 1

Ratio to which the specification applies 1

Rated symmetrical short-circuit current factor Kssc

Rated symmetrical short-circuit current factor Kssc

Duty cycle, consisting of

for C-O cycle: t’al Rated transient dimensioning factor Ktd

for C-O-C-O cycle: t’al, t’, tfr, t’’al Rated secondary loop time constant TS 2

Rated primary time constant Tp

Rated resistive burden Rb Rated resistive burden Rb

998 Note 1: 999 If not specified, for multi-ratio transformers with tappings on the secondary winding, the accuracy requirements 1000 refer to the highest transformation ratio. It has to be considered, that usually the given accuracy requirements can 1001 be fulfilled for one ratio only. 1002

Note 2: for TPY cores only 1003

5.200 Standard values of rated primary current 1004

5.200.1 Single ratio transformers 1005

The standard values of rated primary currents are: 1006

10 – 12,5 – 15 – 20 – 25 – 30 – 40 – 50 – 60 – 75 A, 1007

and their decimal multiples or fractions. 1008

The preferred values are those underlined. 1009

61869-2 ed. 1 © IEC 38/404/CDV - 33 -

5.200.2 Multi-ratio transformers 1010

The standard values given in 5.200.1 refer to the lowest values of rated primary current. 1011

5.201 Standard values of rated secondary currents 1012

The standard values of rated secondary currents are 1 A, 2 A and 5 A 1013

For protective current transformers for transient performance, the standard value of the rated 1014 secondary current is 1 A. 1015

5.202 Rated continuous thermal current 1016

The standard value of rated continuous thermal current is the rated primary current. 1017

When a rated continuous thermal current greater than rated primary current is specified, the 1018 preferred values are 120 %, 150 % and 200 % of rated primary current. 1019

5.203 Short-time current ratings 1020

All current transformers shall comply with the following requirements 1021

5.203.1 Rated short-time thermal current (Ith) 1022

A rated short-time thermal current (Ith) shall be assigned to the transformer (see 3.4.202). 1023

5.203.2 Rated dynamic current (Idyn) 1024

The value of the rated dynamic current (Idyn) shall normally be 2.5 times the rated short-time 1025 thermal current (Ith) and it shall be indicated on the rating plate when it is different from this 1026 value (see 3.3.203). 1027

1028 1029

61869-2 ed. 1 © IEC 38/404/CDV - 34 -

6 Design and construction 1030

6.1 Requirements for liquids used in equipment 1031

6.1.1 General 1032

6.1.2 Liquid quality 1033

6.1.3 Liquid level device 1034

6.1.4 Liquid tightness 1035

6.2 Requirements for gases used in equipment 1036

6.2.1 General 1037

6.2.2 Gas quality 1038

6.2.3 Gas monitoring device 1039

6.2.4 Gas tightness 1040

6.2.4.1 General 1041

6.2.4.2 Closed pressure systems for gas 1042

6.2.5 Pressure relief device 1043

6.3 Requirements for solid materials used in equipment 1044

6.4 Requirements for temperature rise of parts and components 1045

6.4.1 General 1046


The temperature rise of a current transformer when carrying a primary current equal to the 1048 rated continuous thermal current, with a unity power-factor burden corresponding to the rated 1049 output, shall not exceed the appropriate value given in table 5 of IEC61869-1. These values 1050 are based on the service conditions given in clause 4 1051

61869-2 ed. 1 © IEC 38/404/CDV - 35 -

6.4.2 Influence of altitude on temperature-rise 1052

6.5 Requirements for earthing of equipment 1053

6.5.1 General 1054

6.5.2 Earthing of the enclosure 1055

6.5.3 Electrical continuity 1056

6.6 Requirements for the external insulation 1057

6.6.1 Pollution 1058

6.6.2 Altitude 1059

6.7 Mechanical requirements 1060

6.8 Multiple chopped impulse on primary terminals 1061

6.9 Internal arc fault protection requirements 1062

6.10 Degrees of protection by enclosures 1063

6.10.1 General 1064

6.10.2 Protection of persons against access to hazardous parts and protection 1065 of the equipment against ingress of solid foreign objects 1066

6.10.3 Protection against ingress of water 1067

6.10.4 Indoor instrument transformers 1068

6.10.5 Outdoor instrument transformers 1069

6.10.6 Protection of equipment against mechanical impact under normal service 1070 conditions 1071

6.11 Electromagnetic Compatibility (EMC) 1072

6.11.1 General 1073

6.11.2 Requirement for Radio Interference Voltage (RIV) 1074

6.11.3 Requirements for immunity 1075

6.11.4 Requirement for transmitted overvoltages 1076

6.12 Corrosion 1077

6.13 Markings 1078

6.13.200 Terminal markings – General rules 1079

In addition to clause 6.13 of IEC 61869-1 the terminal markings shall identify 1080

a) the primary and secondary windings; 1081 b) the winding sections, if any; 1082 c) the relative polarities of windings and winding sections; 1083 d) the intermediate tapings, if any. 1084

61869-2 ed. 1 © IEC 38/404/CDV - 36 -

6.13.200.1 Method of marking 1085

The marking shall consist of letters followed, or preceded where necessary, by numbers. The 1086 letters shall be in block capitals. 1087

6.13.200.2 Markings to be used 1088

The markings of current transformer terminals shall be as indicated in the following 1089 Table 208. 1090

Table 208 – Markings of terminals 1091

Primary terminals

Secondary terminals

Figure 1 – Single ratio transformer.

Figure 2 – Transformer with an inter-mediate tapping on secondary winding.

Primary terminals

Secondary terminals

Figure 3 – Transformer with primary winding in 2 sections intended for connections either in series or in parallel.

Figure 4 – Transformer with 2 secondary windings; each with its own magnetic core. (Two alternative markings for the secondary terminals.)

6.13.200.3 Indication of relative polarities 1092

All the terminals marked P1, S1 and C1 shall have the same polarity at the same instant. 1093

6.13.201 Rating plate markings 1094

In addition to previous paragraphs, all current transformers shall carry at least the following 1095 markings: 1096

a) the rated primary and secondary current, i.e.: 1097

kr = Ipr / Isr (e.g. 100/5 A) 1098

b) the rated output and the corresponding accuracy class, together with additional 1099 information specified in the later parts of these recommendations (see 6.13.202 and/or 1100 6.13.203, 6.13.204 and 6.13.205); 1101

In addition, the following information shall be marked: 1102 c) the rated short-time thermal current (Ith) and the rated dynamic current if it differs from 2,5 1103

times the rated short-time thermal current (e.g. 13 kA or 13/40 kA); 1104

P2 P1

S2S1

P2P1

S3 S2 S1

S 2 2 S 2

1 S 1 1 S 1

2

P2P1

2S2 1S2 1S1 2S1

P2P1

S2S1

C1 C2

61869-2 ed. 1 © IEC 38/404/CDV - 37 -

d) on transformers with two or more secondary windings, the use of each winding and its 1105 corresponding terminals 1106

e) the rated continuous thermal current 1107

Examples: 1108

For single core current transformer with secondary taps: Icth = 120 % 1109

For multiple core current transformer (300/5 A and 4000/1 A): Icth = 360 A 1110

For current transformer with primary reconnection (4x300/1 A): Icth = 4x360 A 1111

6.13.202 Marking of the rating plate of a measuring current transformer 1112

The accuracy class and instrument security factor shall be indicated following the indication of 1113 corresponding rated output (e.g. 15 VA class 0.5 FS 10). 1114

Current transformers having an extended current rating (see 5.6.200.4) shall have this rating 1115 indicated immediately following the class designation (e.g. 15 VA class 0.5 ext. 150 %). 1116

For current transformers having a rated burden not exceeding 15 VA and an extended burden 1117 down to 1 VA, this rating shall be indicated immediately before the burden indication (for 1118 example, 1..10 VA class 0,2). 1119

NOTE The rating plate may contain information concerning several combinations of ratios, output and accuracy 1120 class that the transformer can satisfy (for example, 15 VA class 0,5 – 30 VA class 1) and in this case non-standard 1121 values of output may be used (for example, 15 VA class 1..7 VA class 0,5 in accordance with note to 5.5). 1122

6.13.203 Marking of the rating plate of a class P protective current transformer 1123

The rating plate shall carry the appropriate information in accordance with 6.13.201. The 1124 rated accuracy limit factor shall be indicated following the corresponding output and accuracy 1125 class (e.g. 30 VA class 5P 10).1 1126

6.13.204 Marking of the rating plate of class PR protective current transformers 1127

The rating plate shall carry the appropriate information in accordance with 6.13.201. The 1128 rated accuracy limit factor shall be indicated following the corresponding output and accuracy 1129 class (e.g. 10 VA class 5PR 30).1 1130

6.13.204.1 Additional marking (when required) 1131

a) secondary loop time constant (Ts) 1132 b) maximum value of secondary winding resistance (Rct) 1133

NOTE 1 A current transformer satisfying the requirements of several combinations of output and accuracy class 1134 and accuracy limit factor may be marked according to all of them. 1135

Example: (30 VA class 1) (15 VA class 1, ext. 150 %) (30 VA class 5PR 10) (15 VA class 5PR 20) 1136 1137

61869-2 ed. 1 © IEC 38/404/CDV - 38 -

1138

6.13.205 Marking of the rating plate of class PX protective current transformers 1139

6.13.205.1 Principal marking 1140

Refer to 6.13.201. The rated turns ratio is given by Ipr and Isr. 1141

6.13.205.2 Additional marking 1142

a) maximum exciting current (Ie) at the rated knee point e.m.f. and/or at the stated 1143 percentage thereof; 1144

b) maximum value of secondary winding resistance (Rct) 1145 c) rated knee point e.m.f. (Ek); 1146

1147 or 1148 1149 dimensioning factor (Kx) 1150 rated resistive burden (Rb). 1151 1152

6.13.205.3 Examples: 1153

1154

Ek=200V Ie<=0.2A Rct<=2.0Ω 1155 1156 or 1157 1158 Ie<=0.2A Rct<=2.0Ω Kx=8 Rb=3.0Ω 1159 1160

6.13.206 Marking of the rating plate of current transformers for transient 1161 performance 1162

6.13.206.1 Principal marking 1163

Refer to 6.13.201 1164

6.13.206.2 Additional marking 1165

1166 Additionally, the class marking consists of the following 2 elements: 1167

a) Definition part (compulsory) 1168 contains the essential information which is necessary to determine whether the current 1169 transformer fulfils given requirements (consisting of duty cycle and Tp) 1170 1171 Examples with Kssc.=20, Ktd=12.5: 1172

Rb 5Ω TPX 20*12.5 Rct 2.8Ω

Rb 5Ω TPY 20*12.5 Rct 2.8Ω Ts 250 ms

Rb 5Ω TPZ 20*12.5 Rct 2.8Ω

1173

b) Complementary part (optional) 1174 1175

61869-2 ed. 1 © IEC 38/404/CDV - 39 -

The complementary part represents one of many possible cycles, leading to the same 1176 value of Ktd. The determination of Ktd is explained in annex B.1. 1177 Examples: 1178

Marking: Meaning:

Cycle 100ms, Tp 100 ms t’al=100ms Tp=100ms

Cycle (40-100)-300-40ms, Tp 100ms t’al=40ms, t’=100ms, tfr=300ms, t’’al=40ms, Tp=100ms

1179

If actual values of Rct have to be mentioned on the rating plate, this value shall fulfill the 1180 following condition: 1181

ctct RRR ≤≤)8.0*( 1182 1183 where R is the measured value. 1184

1185

6.14 Fire hazard 1186

7 Tests 1187

7.1 General 1188

7.1.1 Classification of tests 1189

7.1.2 List of tests 1190

The list of tests is given in Table 209. 1191

Table 209 – List of tests 1192

T e s t s Subclause

Type tests 7.2

Temperature-rise test 7.2.2

Impulse voltage test on primary terminals 7.2.3

Wet test for outdoor type transformers 7.2.4

Electromagnetic Compatibility tests 7.2.5

Test for accuracy 7.2.6

Verification of the degree of protection by enclosures 7.2.7

Enclosure tightness test at ambient temperature 7.2.8

Pressure test for the enclosure 7.2.9

Short-time current test 7.2.200

Routine tests 7.3

Power-frequency voltage withstand tests on primary terminals 7.3.1

Partial discharge measurement 7.3.2

Power-frequency voltage withstand tests between sections 7.3.3

Power-frequency voltage withstand tests on secondary terminals 7.3.4

Test for accuracy 7.3.5

Verification of markings 7.3.6

Enclosure tightness test at ambient temperature 7.3.7

Pressure test for the enclosure 7.3.8

61869-2 ed. 1 © IEC 38/404/CDV - 40 -

Inter-turn overvoltage test 7.3.200

Special tests 7.4

Chopped impulse voltage withstand test on primary terminals 7.4.1

Multiple chopped impulse test on primary terminals 7.4.2

Measurement of capacitance and dielectric dissipation factor 7.4.3

Transmitted overvoltage test 7.4.4

Mechanical tests 7.4.5

Internal arc fault test 7.4.6

Enclosure tightness test at low and high temperatures 7.4.7

Gas dew point test 7.4.8

Corrosion test 7.4.9

Fire hazard test 7.4.10

Sample tests 7.5

1193 1194 1195 For testing of gas-insulated instrument transformers, the type and pressure of the gas shall be 1196 according to Table 210 1197

Table 210 – Gas type and pressure during type, routine and special tests 1198 1199

Test Gas type Pressure

Dielectric,

RIV

Accuracy

Temperature rise

Same fluid as in service Minimum functional pressure

Internal arc

Short-circuit

Mechanical

Tightness

Gas dew point

Same fluid as in service Rated filling pressure

Transmitted overvoltages n/a Reduced pressure

a For gas-insulated instrument transformers installed on GIS, the wet test and RIV test are not applicable.

1200 1201

7.1.3 Sequence of tests 1202

7.2 Type tests 1203

7.2.1 General 1204

7.2.1.1 Information for identification of specimen 1205

7.2.1.2 Information to be included in type-test reports 1206

7.2.2 Temperature-rise test 1207

7.2.2.200 General 1208

For current transformers in three phase gas-insulated metal enclosed switchgear, all three 1209 phases have to be tested in the same time. 1210

61869-2 ed. 1 © IEC 38/404/CDV - 41 -

The current transformer shall be mounted in a manner representative of the mounting in 1211 service and the secondary windings shall be loaded with the designated burdens. However, 1212 because the position of the current transformer in each switchgear can be different, it is left to 1213 the manufacturer’s choice how to arrange the test set up. 1214

7.2.2.201 Cooling-air temperature 1215

The sensors to measure the ambient temperature shall be distributed around the current 1216 transformer, at an appropriate distance according to the current transformer ratings and at 1217 about half-height of the transformer, protected from direct heat radiation. 1218

To minimise the effects of variation of cooling-air temperature, particularly during the last test 1219 period, appropriate means should be used for the temperature sensors such as heat sinks of 1220 time constant approximately equal to that of the transformer. 1221

The average readings of two sensors shall be used for the test. 1222

7.2.2.202 Duration of the test 1223

The test can be stopped when the following conditions are met: 1224

- the test duration is at least equal to three times the current transformer thermal time 1225 constant 1226

- the rate of temperature rise of the windings and of the top-oil immersed current 1227 transformer does not exceed 1 K per hour, during three consecutive temperature rise 1228 readings. 1229

The manufacturer shall estimate the thermal time constant by one of the following 1230 methods: 1231

- before the test, based on the results of previous tests on a similar design and shall be 1232

confirmed during the temperature rise test 1233

- during the test, from the temperature rise curve(s) or temperature decrease curve(s) 1234

recorded during the course of the test and calculated according to Annex C 1235

- during the test, as the point of intersection between the tangent to the temperature 1236

rise curve originating at 0 and the maximum estimated temperature rise 1237

- during the test, as the time elapsed until 63 % of maximum estimated temperature 1238

rise. 1239

7.2.2.203 Temperatures and temperature rises 1240

The purpose of the test is to determine the average temperature rise of the windings and, for 1241 oil-immersed transformers the temperature rise of the top oil, in steady state conditions when 1242 the specified losses are injected in the current transformer. 1243

The average temperature of the windings shall, when practicable, be determined by the 1244 resistance variation method, but for windings of very low resistance thermometers, 1245 thermocouple or other appropriate temperature sensors may be employed. 1246

Thermometers or thermocouples shall measure the temperature rise of parts other than 1247 windings. The top oil temperature shall be measured by sensors applied to the top of metallic 1248 head directly in contact with the oil. 1249

The temperature rises shall be determined by the difference in respect to the ambient 1250 temperature measured as indicated in 7.2.2.201 1251

61869-2 ed. 1 © IEC 38/404/CDV - 42 -

7.2.2.204 Test modalities for current transformers having Um <525 kV 1252

The test shall be performed applying to the primary winding the rated continuous thermal 1253 current with the secondary(s) closed on the rated burden. 1254

7.2.2.205 Test modalities for oil-immersed current transformers having Um ≥ 1255 525 kV 1256

The test shall be performed applying simultaneously to the current transformer: 1257

• the rated continuous thermal current to the primary winding with the secondary winding(s) 1258 closed on the rated burden; 1259

• the highest voltage of the equipment divided by √3 between the primary winding and earth 1260 at which also a terminal of the secondary winding(s) shall be connected. 1261

Note - The test current can be also applied to one or more secondary windings with the primary and the non-1262 supplied secondary windings short-circuited. 1263 1264

7.2.3 Impulse voltage withstand test on primary terminals 1265

The test voltage shall be applied between the terminals of the primary winding (connected 1266 together) and earth. The frame, case (if any), and core (if intended to be earthed) and all 1267 terminals of the secondary winding(s) shall be connected to earth. 1268

7.2.3.1 General 1269

Clause 7.2.3.1 of IEC 61869-1 is applicable with the addition of the following: 1270

For three-phase current transformers for gas insulated substation, each phase shall be tested, 1271 one by one. During the test on each phase, the other phases will be earthed. 1272

For the acceptance criteria of gas-insulated metal enclosed transformers, refer to IEC 62271-1273 203 clause 6.2.4. 1274

61869-2 ed. 1 © IEC 38/404/CDV - 43 -

7.2.3.2 Lightning impulse voltage test on primary terminals 1275

7.2.3.2.1 Instrument transformers having Um < 300 kV 1276

7.2.3.2.2 Instrument transformers having Um ≥ 300 kV 1277

7.2.3.3 Switching impulse voltage test 1278

7.2.3.3.1 General 1279

7.2.4 Wet test for outdoor type transformers 1280

7.2.5 Electromagnetic Compatibility (EMC) tests 1281

7.2.5.1 RIV test 1282

7.2.5.2 Immunity test 1283

7.2.5.3 Not applicable 1284

7.2.6 Test for accuracy 1285

7.2.6.200 Test for accuracy of measuring current transformers 1286

Type tests to prove compliance with 5.6.200.3 shall, in the case of transformers of classes 0.1 1287 to 1, be made at each value of current given in Table 201 at 25 % and at 100 % of rated 1288 burden (subject to 1 VA minimum). 1289

Transformers having extended current ratings greater than 120 % shall be tested at the rated 1290 extended primary current instead of at 120 % of rated current. 1291

Transformers of class 3 and class 5 shall be tested for compliance with the two values of 1292 current given in Table 203 at 50 % and at 100 % of rated burden. 1293

7.2.6.201 Test for current error and phase displacement of protective 1294 current transformers 1295

Tests shall be made at rated primary current to prove compliance with 5.6.201.1.4 in respect 1296 of current error and phase displacement. 1297

7.2.6.202 Test for composite error 1298

a) Compliance with the limits of composite error given in Table 204 shall be demonstrated by 1299 a direct test in which a substantially sinusoidal current equal to the rated accuracy limit 1300 primary current is passed through the primary winding with the secondary winding 1301 connected to a burden of magnitude equal to the rated burden but having, at the discretion 1302 of the manufacturer, a power-factor between 0,8 inductive and unity (see annexes A.4, 1303 A.5, A.6, A.7 ). 1304

The test may be carried out on a transformer similar to the one being supplied, except that 1305 reduced insulation may be used, provided that the same geometrical arrangement is 1306 retained. 1307

NOTE Where very high primary currents and single bar-primary winding current transformers are concerned, 1308 the distance between the return primary conductor and the current transformer should be taken into account 1309 from the point of view of reproducing service conditions. 1310

b) For current transformers having substantially continuous ring cores, uniformly distributed 1311 secondary winding(s) or uniformly distributed portions of tapped winding(s) and having 1312 either a centrally located primary conductor(s) or a uniformly distributed primary winding, 1313 the direct test may be replaced by the following indirect test, provided that the effect of the 1314 return primary conductor(s) is negligible. 1315

61869-2 ed. 1 © IEC 38/404/CDV - 44 -

With the primary winding open-circuited, the secondary winding is energized at rated 1316 frequency by a substantially sinusoidal voltage having an r.m.s. value equal to the 1317 secondary limiting e.m.f. 1318

The resulting exciting current, expressed as a percentage of the rated secondary current 1319 multiplied by the accuracy limit factor, shall not exceed the limit of composite error given 1320 in table 204. 1321

NOTE 1 In calculating the secondary limiting e.m.f., the secondary winding impedance should be assumed to 1322 be equal to the secondary winding resistance measured at room temperature and corrected to 75 °C. 1323

NOTE 2 In determining the composite error by the indirect method, a possible difference between turns ratio 1324 and rated transformation ratio need not be taken into account. 1325

7.2.6.203 Proof of low leakage reactance type 1326

Current transformers shall, in addition to the requirements of clause 7.2, be tested as 1327 prescribed below. 1328

In order to establish proof of low leakage reactance design, it shall be shown by a drawing 1329 that the current transformer has a substantially continuous ring core, with air gaps uniformly 1330 distributed, if any, uniformly distributed secondary winding, a primary conductor symmetrical 1331 with respect to rotation and the influences of conductors of the adjacent phase outside of the 1332 current transformer housing and of the neighbouring phases are negligible. If compliance with 1333 the requirements of low leakage reactance design cannot be established to the mutual 1334 satisfaction of the manufacturer and purchaser by reference to drawings, then the composite 1335 error shall be determined for the complete secondary winding using either of the direct 1336 methods of test given in annexes A.5 or A.6, at a secondary current of Kx ⋅ Isn and with a 1337 secondary burden Rb. Proof of low leakage reactance design shall be considered to have 1338 been established if the value of composite error from the direct method of test is less than 1,1 1339 times that deduced from the secondary excitation characteristic. 1340

NOTE The value of primary current required to perform direct composite error tests on certain transformer types 1341 may be beyond the capability of facilities normally provided by manufacturers. Tests at lower levels of primary 1342 current may be agreed between the manufacturer and purchaser. 1343

7.2.6.204 Additional type tests for protective current transformers for 1344 transient performance 1345

To prove compliance of the current transformer with the requirements of this standard, the 1346 following additional tests shall be performed. 1347

Table 211 – Additional type tests for protective current transformers for transient 1348 performance 1349

1350

Test Protection class Reference

TPX TPY TPZ

Determination of the secondary winding resistance Rct

X

X

X

7.2.6.204.1

Determination of the steady state ratio error and phase displacement

X

X

X

7.2.6.204.2

Determination of the secondary loop time constant Ts

X

7.2.6.204.3

61869-2 ed. 1 © IEC 38/404/CDV - 45 -

Determination of the magnetic characteristic

X

7.2.6.204.4

Determination of the Error at limiting conditions

X

X

X

7.2.6.204.5

1351 1352 1353

7.2.6.204.1 Determination of the secondary winding resistance Rct 1354

The secondary winding resistance shall be measured and corrected to 75 ºC. 1355 1356 1357

7.2.6.204.2 Determination of the steady state ratio error and phase 1358 displacement 1359

The ratio error and the phase displacement shall be measured at rated current. 1360 The results shall correspond to a secondary winding temperature of 75 °C. 1361 Therefore the actual value of the secondary winding temperature shall be measured, and the 1362 difference to its value corrected to 75°C shall be determined. The error measurement shall be 1363 made with the burden Rb increased by the above mentioned difference of winding resistance. 1364 1365 1366 Alternatively, for TPY and TPZ cores the phase displacement at 75°C ( 75ϕ∆ ) may be 1367

determined by measuring at ambient temperature ( ambϕ∆ ) and calculating as follows: 1368 1369 1370

bambct

bctamb RR

RR+

+∆=∆ ϕϕ75 1371

1372 where ambctR is the winding resistance at the ambient temperature. The ratio error is not 1373 affected by this resistance correction. 1374 1375 1376 For type and routine testing, a direct test method (using a primary current source and a 1377 reference current transformer) has to be applied. 1378 1379 For low leakage reactance CT’s, an indirect test method is given in annex B.4. 1380 It may be applied for on-site measurements and for monitoring purposes. 1381 1382

61869-2 ed. 1 © IEC 38/404/CDV - 46 -

1383 1384

7.2.6.204.3 Determination of the secondary time constant Ts 1385

The secondary loop time constant (Ts) shall be determined and shall not differ from the 1386 value on the rating plate by more than ±30 % for class TPY and ±10 % for class TPZ 1387 current transformers. In general, Ts shall be determined according to the following equation: 1388 1389 1390

)tan(*1

ϕω ∆=ST 1391

1392 If ϕ∆ is expressed in minutes, the following approximate formula may be applied: 1393

1394

ωϕ ⋅∆

=[min]3438][sTS 1395

1396 1397 Since this method may cause difficulties for high ratio transformers and small phase angles 1398 due to uncertainty of the measurement of low phase displacement, an alternative method may 1399 be used in these cases by calculation of TS using the value of Lm (see clause - 46 -) 1400 1401

)( bct

mS RR

LT+

= 1402

7.2.6.204.4 Determination of the magnetic characteristic 1403

1404 a) magnetising inductance Lm 1405 1406 The magnetising inductance Lm shall be determined by one of the methods described in 1407 annex B.2. 1408 1409 1410 b) remanence factor (Kr ) 1411

The remanence factor (Kr) shall be determined to prove compliance with clause 5.6.201.4.3. 1412 For test methods, refer to annex B.2. 1413

1414 Note: This type test shall be performed for each specific realization of current transformer. Usually, it is made for 1415 each production series. 1416 1417

7.2.6.204.5 Determination of the error at limiting conditions 1418

The purpose of the type test is to prove the compliance with the requirements at limiting 1419 conditions. For test methods refer to annex B.3. 1420 1421 The direct test may be replaced by an indirect test, if at least one of the following two conditions is 1422 fulfilled: 1423 1424

a) The current transformer is of the low leakage reactance type (see 7.2.6.203) 1425 1426

b) A type test report of a current transformer is available, having 1427 - substantially the same construction and 1428 - similar rated primary short-circuit current. 1429 1430

1431 The test can be performed on a full scale model of the active part of the current transformer 1432 assembly inclusive of all metal housings but without insulation. 1433

61869-2 ed. 1 © IEC 38/404/CDV - 47 -

1434 If compliance between direct and indirect test is given, a type test shall be declared as 1435 relevant for similar designs (dimensions, electrical requirements). 1436 1437 If Fc is greater than 1.1, it shall be considered in the dimensioning of the core. 1438 1439

7.2.7 Verification of the degree of protection by enclosures 1440

7.2.7.1 Verification of the IP coding 1441

7.2.7.2 Mechanical impact test 1442

7.2.8 Enclosure tightness test at ambient temperature 1443


7.2.9 Pressure test for the enclosure 1445

7.2.200 Short-time current test 1446

This test shall be made with the secondary winding(s) short-circuited, and at a current I for a 1447 time t, so that (I 2t) is not less than (I 2

th) * 1s and provided t has a value between 0,5 s and 5 1448 s. 1449

The dynamic test shall be made with the secondary winding(s) short-circuited, and with a 1450 primary current the peak value of which is not less than the rated dynamic current (Idyn) for at 1451 least one peak. 1452

The dynamic test may be combined with the thermal test above, provided the first major peak 1453 current of that test is not less than the rated dynamic current (Idyn). 1454

The transformer shall be deemed to have passed these tests if, after cooling to ambient 1455 temperature (between 10 °C and 40 °C), it satisfies the following requirements: 1456

a) it is not visibly damaged; 1457 b) its errors after demagnetization do not differ from those recorded before the tests by more 1458

than half the limits of error appropriate to its accuracy class; 1459 c) it withstands the dielectric tests specified in 7.3.1, 7.3.2, 7.3.3 and 7.3.4, but with the test 1460

voltages or currents reduced to 90 % of those given; 1461 d) on examination, the insulation next to the surface of the conductor does not show 1462

significant deterioration (e.g. carbonization). 1463

The examination d) is not required if the current density in the primary winding, corresponding 1464 to the rated short-time thermal current (Ith), does not exceed: 1465

– 180 A/ mm2 where the winding is of copper of conductivity not less than 97 % of the value 1466 given in IEC 60028. 1467

– 120 A/ mm2 where the winding is of aluminium of conductivity not less than 97 % of the 1468 value given in IEC 60121. 1469

NOTE Experience has shown that in service the requirements for thermal rating are generally fulfilled in the case 1470 of class A insulation, provided that the current density in the primary winding, corresponding to the rated short-time 1471 thermal current, does not exceed the above-mentioned values. 1472

1473

1474

61869-2 ed. 1 © IEC 38/404/CDV - 48 -

7.3 Routine tests 1475

7.3.1 Power-frequency voltage withstand tests on primary terminals 1476


The test voltage shall be applied between the short-circuited primary winding and earth. The 1478 short-circuited secondary winding(s), the frame, case (if any) and core (if there is a special 1479 earth terminal) shall be connected to earth. 1480

7.3.2 Partial discharge measurement 1481

7.3.2.1 Test circuit and instrumentation 1482

7.3.2.2 Partial discharge test procedure 1483

7.3.3 Power-frequency voltage withstand tests between sections 1484

7.3.4 Power-frequency voltage withstand tests on secondary terminals 1485

Test shall be performed to demonstrate compliance with 5.3.5 1486

7.3.5 Test for accuracy 1487

7.3.5.200 Tests for accuracy of measuring current transformers 1488

The routine test for accuracy is in principle the same as the type test in 7.2.6.200, but routine 1489 tests at a reduced number of currents and/or burdens are permissible provided it has been 1490 shown by type tests on a similar transformer that such a reduced number of tests are 1491 sufficient to prove compliance with 5.6.200.3 1492

7.3.5.201 Instrument security factor (FS) 1493

A test may be performed using the following indirect test: 1494

– with the primary winding open-circuited, the secondary winding is energized at rated 1495 frequency by a substantially sinusoidal voltage having an r.m.s. value equal to the 1496 secondary limiting e.m.f. 1497

The resulting exciting current (Ie), expressed as a percentage of the rated secondary current 1498 (Isr) multiplied by the instrument security factor FS shall be equal to or exceed the rated value 1499 of the composite error of 10 %: 1500

%% FSI

Isr

e 10100 ≥⋅⋅

1501

If this result of measurement should be called into question, a controlling measurement shall 1502 be performed with the direct test (see annexes A.5, A.6), the result of which is then 1503 mandatory. 1504

NOTE The great advantage of the indirect test is that high currents are not necessary (for instance 30 000 A at a 1505 primary rated current 3000 A and an instrument security factor 10) and also no burdens which must be constructed 1506 for 50 A. The effect of the return primary conductors is not physically effective at the indirect test. Under service 1507 conditions the effect can only enlarge the composite error, which is desirable for the safety of the apparatus 1508 supplied by the measuring transformer. 1509

7.3.5.202 Tests for current error and phase displacement of class P 1510 protective current transformers 1511

Tests shall be made at rated primary current to prove compliance with 5.6.201.1.4 in respect 1512 of current error and phase displacement. 1513

61869-2 ed. 1 © IEC 38/404/CDV - 49 -

7.3.5.203 Test for composite error 1514

For all transformers qualifying under item b) of 7.2.6.202, the routine test is the same as the 1515 type test. 1516

For other transformers, the indirect test of measuring the exciting current may be used, but a 1517 correction factor shall be applied to the results, the factor being obtained from a comparison 1518 between the results of direct and indirect tests applied to a transformer of the same type as 1519 the one under consideration (see note 2), the accuracy limit factor and the conditions of 1520 loading being the same. 1521

In such cases, certificates of test should be held available by the manufacturer. 1522

NOTE 1 The correction factor is equal to the ratio of the composite error obtained by the direct method and the 1523 exciting current expressed as a percentage of the rated secondary current multiplied by the accuracy limit factor, 1524 as determined by the indirect method specified in item a) of 7.2.6.201 1525

NOTE 2 The expression “transformer of the same type” implies that the ampere turns are the same irrespective of 1526 ratio, and that the geometrical arrangements, magnetic materials and the secondary windings are identical. 1527

7.3.5.204 Test for current error and phase displacement of class PR 1528 protective current transformers 1529

Class PR current transformers shall, in addition to the requirements of clause 7.3.5.202 and 1530 7.3.5.203, be subjected to the routine tests prescribed below. 1531

7.3.5.204.1 Determination of remanence factor (Kr) 1532

The remanence factor (Kr) shall be determined to prove compliance with clause 5.6.201.2.5. 1533 For test methods, refer to annex B.2. 1534

7.3.5.204.2 Determination of secondary loop time constant (Ts) 1535

The secondary loop time constant (Ts) shall be determined. It shall not differ from the 1536 specified value by more than ±30 %. For determination methods, refer to 7.2.6.204.3 1537

7.3.5.204.3 Determination of secondary winding resistance (Rct) 1538

The secondary winding resistance shall be measured and an appropriate correction applied if 1539 the measurement is made at a temperature which differs from 75°C or such other temperature 1540 as may have been specified. The value so adjusted is the rated value for Rct. 1541 1542 NOTE For determination of secondary loop resistance (Rs = Rct + Rb), Rb is the rated resistive burden which, in 1543 the case of class PR current transformers, is taken as being equal to the resistive part of the burden used in 1544 accordance with 5.6.201.1.4 for the determination of current error and phase displacement. 1545

7.3.5.205 Tests for class PX protective current transformers 1546

Class PX current transformers shall be tested as prescribed below. 1547

7.3.5.205.1 Rated knee point e.m.f. (Ek) and maximum exciting current (Ie) 1548

A sinusoidal e.m.f. of rated frequency equal to the rated knee-point e.m.f. shall be applied to 1549 the complete secondary winding, all other windings being open-circuited and the exciting 1550 current measured. 1551

The e.m.f. shall then be increased by 10 % and the exciting current shall not increase by more 1552 than 50 %. The exciting voltage shall be measured with an instrument which has a response 1553 proportional to the average value, but calibrated in r.m.s. The exciting current shall be 1554 performed using an r.m.s measuring instrument having a minimum crest factor of at least 3. 1555

61869-2 ed. 1 © IEC 38/404/CDV - 50 -

Other measurement methods may not deliver the correct results because of the non-1556 sinusoidal nature of the measured signal 1557

The excitation characteristic shall be plotted at least up to the rated knee point e.m.f. The 1558 exciting current (Ie) at the rated knee-point e.m.f. and at any stated percentage, shall not 1559 exceed the rated value. The number of measurement points shall be agreed between the 1560 manufacturer and the purchaser. 1561

7.3.5.205.2 Secondary winding resistance (Rct) 1562

The resistance of the complete secondary winding shall be measured. The value obtained 1563 when corrected to 75 °C shall not exceed the specified value. 1564

7.3.5.205.3 Turns ratio error (εt) 1565

The turns ratio shall be determined in accordance with Annex D. The turn’s ratio error shall 1566 not exceed the value given in c). 1567

NOTE A simplified test involving measurement of the ratio error with zero connected burden may be substituted 1568 by agreement between the manufacturer and purchaser. 1569

7.3.5.206 Additional routine tests for protective current transformers for 1570 transient performance 1571

7.3.5.206.1 Determination of the secondary winding resistance Rct 1572

This test is identical with the type test described in 7.2.6.204.1 1573

7.3.5.206.2 Determination of the steady state ratio error and phase 1574 displacement 1575


7.3.5.206.3 Determination of the secondary time constant Ts 1577


7.3.5.206.4 Determination of the error at limiting conditions 1579

The routine test shall be made as an indirect test according to 7.2.6.204.5 1580 1581

7.3.6 Verification of markings 1582

7.3.7 Enclosure tightness test at ambient temperature 1583


7.3.7.2 Liquid systems 1585

7.3.8 Pressure test for the enclosure 1586

7.3.200 Inter-turn overvoltage test 1587

Tests shall be performed to demonstrate compliance with 5.3.200. 1588

The inter-turn overvoltage test shall be performed in accordance with one of the following procedures. 1589

If not otherwise agreed, the choice of the procedure is left to the manufacturer. 1590

61869-2 ed. 1 © IEC 38/404/CDV - 51 -

Procedure A: with the secondary windings open-circuited (or connected to a high impedance 1591 device which reads peak voltage), a substantially sinusoidal current at a frequency between 1592 40 Hz and 60 Hz (in accordance with IEC 60060-1) and of r.m.s. value equal to the rated 1593 primary current (or rated extended primary current (see 5.6.200.4) when applicable) shall be 1594 applied for 60 s to the primary winding. 1595

The applied current shall be limited if the test voltage of 4,5 kV peak is obtained before 1596 reaching the rated current (or extended rated current). 1597

Procedure B: with the primary winding open-circuited, the prescribed test voltage (at some 1598 suitable frequency) shall be applied for 60 s to the terminals of each secondary full winding, 1599 providing that the r.m.s. value of the secondary current does not exceed the rated secondary 1600 current (or rated extended current). 1601

The value of the test frequency shall be not greater than 400 Hz. 1602

At this frequency, if the voltage value achieved at the rated secondary current (or rated 1603 extended current) is lower than 4,5 kV peak, the obtained voltage is to be regarded as the test 1604 voltage. 1605

When the frequency exceeds twice the rated frequency, the duration of the test may be 1606 reduced from 60 s as below: 1607

frequencytest

frequencyratedthetwices)(testofduration ⋅= 60 1608

with a minimum of 15 s. 1609

NOTE The inter-turn overvoltage test is not a test carried out to verify the suitability of a current transformer to 1610 operate with the secondary winding open-circuited. Current transformers should not be operated with the 1611 secondary winding open-circuited because of the potentially dangerous overvoltages and overheating which can 1612 occur. 1613

1614

1615

7.4 Special tests 1616

7.4.1 Chopped impulse voltage withstand test on primary terminals 1617

7.4.2 Multiple chopped impulse test on primary terminals 1618

7.4.3 Measurement of capacitance and dielectric dissipation factor 1619

Clause 7.4.3 of IEC 61869-1 is applicable but with the addition of the following: 1620

The test voltage shall be applied between the short-circuited primary winding terminals and 1621 earth. Generally the short-circuited secondary winding(s), any screen, and the insulated metal 1622 casing shall be connected to the measuring bridge. If the current transformer has a special 1623 device (terminal) suitable for this measurement, the other low-voltage terminals shall be 1624 short-circuited and connected together with the metal casing to the earth or the screen of the 1625 measuring bridge. 1626

NOTE In some cases, it is necessary to connect the earth to other points of the bridge. 1627

The test shall be performed with the current transformer at ambient temperature, the value of 1628 which shall be recorded. 1629

61869-2 ed. 1 © IEC 38/404/CDV - 52 -

7.4.4 Transmitted overvoltage test 1630

7.4.5 Mechanical tests 1631

7.4.6 Internal arc fault test 1632

Clause 7.4.6 of IEC 61869-1 is applicable with the addition of the following note: 1633

NOTE: For top core oil-immersed current transformers, the area in which failure in service incept in many cases is 1634 located in the upper part of the main insulation. For hair pin oil-immersed current transformers this area is 1635 generally located in the bottom part of the main insulation. 1636

7.4.7 Enclosure tightness tests at low and high temperatures 1637

7.4.8 Gas Dew point test 1638

7.4.9 Corrosion test 1639

7.4.9.1 Test procedure 1640

7.4.9.2 Criteria to pass the test 1641

7.4.10 Fire hazard test 1642

7.5 Sample tests 1643

8 Rules for transport, storage, erection, operation and maintenance 1644

9 Safety 1645

10 Influence of products on the natural environment 1646

1647 1648 1649

1650

61869-2 ed. 1 © IEC 38/404/CDV - 53 -

Annex A 1651 Protective current transformers classes P, PR, PX (Normative) 1652

A.1 Vector diagram 1653

If consideration is given to a current transformer which is assumed to contain only linear 1654 electric and magnetic components in itself and in its burden, then, under the further 1655 assumption of sinusoidal primary current, all the currents, voltages and fluxes will be 1656 sinusoidal, and the performance can be illustrated by a vector diagram such as figure 2A.1. 1657

1658

1659

1660

1661

1662

Figure 2A.1 1663

In figure 2A.1, Is represents the secondary current. It flows through the impedance of the 1664 secondary winding and the burden which determines the magnitude and direction of the 1665 necessary induced voltage Es and of the flux Φ which is perpendicular to the voltage vector. 1666 This flux is maintained by the exciting current Ie, having a magnetizing component Im parallel 1667 to the flux Φ, and a loss (or active) component Ia parallel to the voltage. The vector sum of the 1668 secondary current Is and the exciting current Ie is the vector I″p representing the primary 1669 current divided by the turns ratio (number of secondary turns to number of primary turns). 1670

Thus, for a current transformer with turns ratio equal to the rated transformation ratio, the 1671 difference in the lengths of the vectors Is and I″p, related to the length of I″p, is the current 1672 error according to the definition of 3.4.3, and the angular difference ∆φ is the phase 1673 displacement according to 3.4.4. 1674

A.2 Turns correction 1675

When the turns ratio is different from (usually less than) the rated transformation ratio, the 1676 current transformer is said to have turns correction. Thus, in evaluating the performance, it is 1677 necessary to distinguish between I″p, the primary current divided by the turns ratio, and I′p, 1678 the primary current divided by the rated transformation ratio. Absence of turns correction 1679 means I′p = I″p. If turns correction is present, I′p is different from I″p, and since I″p is used in 1680 the vector diagram and I′p is used for the determination of the current error, it will be seen 1681 that turns correction has an influence on the current error (and may be used deliberately for 1682 that purpose). However, the vectors I′p and I″p have the same direction, so turns correction 1683 has no influence on phase displacement. 1684

It will also be apparent that the influence of turns correction on composite error is less than its 1685 influence on current error. 1686

A.3 The error triangle 1687

In figure 2A.2, the upper part of figure 2A.1 is re-drawn to a larger scale and under the further 1688 assumption that the phase displacement is so small that for practical purposes the two 1689 vectors Is and I″p can be considered to be parallel. Assuming again that there is no turns 1690

Φ

∆φ δ

O

le

ls l”p

le la

lm

Es

61869-2 ed. 1 © IEC 38/404/CDV - 54 -

correction, it will be seen by projecting Ie to Ip that with a good approximation the in-phase 1691 component (∆I) of Ie can be used instead of the arithmetic difference between I″p and Is to 1692 obtain the current error and, similarly, the quadrature component (∆ Iq) of Ie can be used to 1693 express the phase displacement. 1694

1695

1696

1697

1698

1699

Figure 2A.2 1700

It will further be seen that under the given assumptions the exciting current Ie divided by I″p is 1701 equal to the composite error according to 3.4.202. 1702

Thus, for a current transformer without turns correction and under conditions where a vector 1703 representation is justifiable, the current error, phase displacement and composite error form a 1704 right-angled triangle. 1705

In this triangle, the hypotenuse representing the composite error is dependent on the 1706 magnitude of the total burden impedance consisting of burden and secondary winding, while 1707 the division between current error and phase displacement depends on the power factors of 1708 the total burden impedance and of the exciting current. Zero phase displacement will result 1709 when these two power factors are equal, i.e. when Is and Ie are in phase. 1710

A.4 Composite error 1711

The most important application, however, of the concept of composite error is under 1712 conditions where a vector representation cannot be justified because non-linear conditions 1713 introduce higher harmonics in the exciting current and in the secondary current (see figure 1714 2A.3). 1715

1716

1717

1718

1719

1720

1721

Figure 2A.3 1722

It is for this reason that the composite error is defined as in 3.4.202 and not in the far simpler 1723 way as the vector sum of current error and phase displacement as shown in figure 2A.2. 1724

Thus, in the general case, the composite error also represents the deviations from the ideal 1725 current transformer that are caused by the presence in the secondary winding of higher 1726

∆lq

ls l”p

le la

lm

∆l

61869-2 ed. 1 © IEC 38/404/CDV - 55 -

harmonics which do not exist in the primary. (The primary current is always considered 1727 sinusoidal for the purposes of this standard.) 1728

A.5 Direct test for composite error 1729

Figure 2A.4 shows a current transformer having a turns ratio of 1/1. It is connected to a 1730 source of primary (sinusoidal) current, a secondary burden ZB with linear characteristics and 1731 to an ammeter in such a manner that both the primary and secondary currents pass through 1732 the ammeter but in opposite directions. In this manner, the resultant current through the 1733 ammeter will be equal to the exciting current under the prevailing conditions of sinusoidal 1734 primary current, and the r.m.s. value of that current related to the r.m.s. value of the primary 1735 current is the composite error according to 3.4.202, the relation being expressed as a 1736 percentage. 1737

1738

1739

1740

1741

Figure 2A.4 1742

Figure 2A.4 therefore represents the basic circuit for the direct measurement of composite 1743 error. 1744

Figure 2A.5 represents the basic circuit for the direct measurement of composite error for 1745 current transformers having rated transformation ratios differing from unity. It shows two 1746 current transformers of the same rated transformation ratio. The current transformer marked N 1747 is assumed to have negligible composite error under the prevailing conditions (minimum 1748 burden), while the current transformer under test and marked X is connected to its rated 1749 burden. 1750

1751

1752

1753

1754

Figure 2A.5 1755

They are both fed from the same source of primary sinusoidal current, and an ammeter is 1756 connected to measure the difference between the two secondary currents. Under these 1757 conditions, the r.m.s. value of the current in the ammeter A2 related to the r.m.s. value of the 1758 current in ammeter A1 is the composite error of transformer X, the relation being expressed as 1759 a percentage. 1760

With this method, it is necessary that the composite error of transformer N is truly negligible 1761 under the conditions of use. It is not sufficient that transformer N has a known composite error 1762 since, because of the highly complicated nature of composite error (distorted waveform), any 1763 composite error of the reference transformer N cannot be used to correct the test results. 1764

∼

P S

P S

A

ZB

P

S

P

S

A2 ZB

X P

S

P

S

A1

N

61869-2 ed. 1 © IEC 38/404/CDV - 56 -

A.6 Alternative method for the direct measurement of composite error 1765

Alternative means may be used for the measurement of composite error and one method is 1766 shown in figure 2A.6. 1767

1768

1769

1770

1771

1772

Figure 2A.6 1773

Whilst the method shown in figure 2A.5 requires a “special” reference transformer N of the 1774 same rated transformation ratio as the transformer X and having negligible composite error at 1775 the accuracy limit primary current, the method shown in figure 2A.6, enables standard 1776 reference current transformers N and N′ to be used at or about their rated primary currents. It 1777 is still essential, however, for these reference transformers to have negligible composite 1778 errors but the requirement is easier to satisfy. 1779

In figure 2A.6 X is the transformer under test, N is a standard reference transformer with a 1780 rated primary current of the same order of magnitude as the rated accuracy limit primary 1781 current of transformer X (the current at which the test is to be made), and N′ is a standard 1782 reference transformer having a rated primary current of the order of magnitude of the 1783 secondary current corresponding to the rated accuracy limit primary current of transformer X. 1784 It should be noted that the transformer N′ constitutes a part of the burden ZB of transformer X 1785 and must therefore be taken into account in determining the value of the burden Z′B. A1 and 1786 A2 are two ammeters and care must be taken that A2 measures the difference between the 1787 secondary currents of transformers N and N′. 1788

If the rated transformation ratio of transformer N is kr, of transformer X is krx and of 1789 transformer N′ is k′r, the ratio kr must equal the product of k′r and krx: 1790

i.e. kr = k′r × krx 1791

Under these conditions, the r.m.s. value of the current in ammeter A2, related to the current in 1792 ammeter A2, is the composite error of transformer X, the relation being expressed as a 1793 percentage. 1794

NOTE When using the methods shown in figures 2A.5 and 2A.6, care should be taken to use a low impedance 1795 instrument for A2 since the voltage across this ammeter (divided by the ratio of transformer N′ in the case of figure 1796 2A.6) constitutes part of the burden voltage of transformer X and tends to reduce the burden on this transformer. 1797 Similarly, this ammeter voltage increases the burden on transformer N. 1798

A.7 Use of composite error 1799

The numeric value of the composite error will never be less than the vector sum of the current 1800 error and the phase displacement (the latter being expressed in centiradians). 1801

Consequently, the composite error always indicates the highest possible value of current error 1802 or phase displacement. 1803

The current error is of particular interest in the operation of overcurrent relays, and the phase 1804 displacement in the operation of phase sensitive relays (e.g. directional relays). 1805

S

S

A2

Z’B

P

S

P

S

A1

N

SS

PP X

P

P

N’

ZB

61869-2 ed. 1 © IEC 38/404/CDV - 57 -

In the case of differential relays, it is the combination of the composite errors of the current 1806 transformers involved which must be considered. 1807

An additional advantage of a limitation of composite error is the resulting limitation of the 1808 harmonic content of the secondary current which is necessary for the correct operation of 1809 certain types of relays. 1810

61869-2 ed. 1 © IEC 38/404/CDV - 58 -

Annex B 1811 Protective current transformers classes for transient performance 1812

(Normative) 1813

B.1 Basic theoretical equations for transient dimensioning 1814

B.1.1 Short-circuit 1815

The general expression for the instantaneous value of a short-circuit current may be written: 1816

⎥⎦⎤

⎢⎣⎡ −+−−

−= )cos()cos(

/2)( ϕγωϕγ tpTt

epscIti (1)

where 1817

pscI Initial ac short-circuit current at accuracy limit of current transformer pnIsscKpscI =

pRpL

pT = Primary time constant

γ Switching or fault inception angle

( )pTpRpX

ωϕ arctanarctan == Phase angle of system short-circuit impedance

when the equivalent voltage source in the short-circuit with pR and pX is 1818

)cos(max)( γω +−= tUtu (2) For simplification purpose the fault inception angle and system impedance angle can be 1819 summed up to one single angle which makes the problem easier to understand from the 1820 mathematical point of view. 1821

ϕγθ −= (3)

⎥⎦⎤

⎢⎣⎡ +−

−= )cos()cos(

/2)( θωθ tpTt

epscIti (4)

The angles θ and γ describe the same problem of variable fault inception angle and therefore 1822 can be used alternating where suitable but according to their definition. 1823 Fig. 2B.1 shows two typical primary short-circuit currents. The first one occurs with a fault 1824 inception angle of °= 90γ which leads to the highest peak current and the highest magnetic 1825 peak flux (Fig. 2B.1) whereas the second one occurs with °= 140γ which leads to a lower 1826

asymmetry. Cases like the latter one is important for short alt when the current and magnetic 1827 flux are higher than in the case for highest peak current. 1828

1829 Fig. 2B.1: Short-circuit current with highest peak (γ = 90°) and lower asymmetry 1830

(γ = 140°) 1831

1832

61869-2 ed. 1 © IEC 38/404/CDV - 59 -

1833 Fig. 2B.2: Magnetic-flux for the two cases in Fig. 2B.1 1834

1835 A possibly reduced range of fault inception angle °≥ 90mγ can be used to define a reduced 1836

asymmetry which may lead to a reduced factor tdK in some special cases. Such calculation 1837 is shown in the application guide to this standard. 1838 1839

B.1.2 Transient factor 1840

The transient dimensioning factor tdK is the final parameter for the core dimensioning and is 1841 given on the rating plate. It can be calculated from different functions of the transient factor 1842

tfK as given in the equations below and showed in Fig. 2B.3. 1843

1844 The transient factor tfK given in this section is derived from the differential equation of the 1845

equivalent circuit with a constant inductivity of the current transformer core, with an ohmic 1846 burden and without consideration of remanence. The exact solution of the differential equation 1847 is given in the application guide whereas the formulas given in this annex are given either as 1848 curve diagrams or as simplified formulas. 1849

tfK and the magnetic flux depend likewise on time and in the end of the accuracy limit time 1850

alt required by the protection system. By calculating with the linear inductivity the solution is 1851 only valid up to the first saturation of the current transformer. 1852 1853 1854 1855

1856 1857

Fig. 2B.3: Relevant time ranges for calculation of transient factor 1858

1859 In some cases the protection system may require a alt which is not constant and depends on 1860 different parameters of the short-circuit current. Therefore the transient dimensioning factor 1861

tdK can also be tested and given by the manufacturer of the protection system. 1862

61869-2 ed. 1 © IEC 38/404/CDV - 60 -

1863 1864 A general overview with a flow chart and with examples is given in the application guide to 1865 this standard. 1866 1867 1868 The typical curve of the transient factor (Fig. 2B.3) consists of three ranges defined by three 1869 functions of tfK : 1870

1871 Range 1: max,0 tfal tt <≤ : 1872

The first range begins at zero time and ends when the curve of max,ψtfK touches its 1873

envelope curve of peaks tfpK at the time 1874

ω

ϕπ +=max,tft (5)

Within this time range max,ψtfK considers the worst case switching angle )( altθ which leads 1875

to the highest flux at the accuracy limit time alt . Figures 2B.4 … 12 show the curves for 1876

different alt and secondary time constants sT versus the primary time constant pT for given 1877

configurations of secondary time constant and frequency. 1878 1879 1880

Fig. 2B.4 Determination of Ktf for δ = 3° (Ts=61

ms) and f=50 Hz

61869-2 ed. 1 © IEC 38/404/CDV - 61 -

Fig. 2B.5 Determination of Ktf for δ = 1.5°

(Ts=122 ms) and f=50 Hz

Fig. 2B.6 Determination of Ktf for δ = 0.1° (Ts=

1.8 s) and f=50 Hz


ms) and f=60 Hz

61869-2 ed. 1 © IEC 38/404/CDV - 62 -


(Ts=100 ms) and f=60 Hz

Fig. 2B.9 Determination of Ktf for δ = 0.1° (Ts=

1.5 s) and f=60 Hz


ms) and f=16.7 Hz

61869-2 ed. 1 © IEC 38/404/CDV - 63 -


(Ts=365 ms) and f=16.7 Hz

Fig. 2B.12 Determination of Ktf for δ = 0.1° (Ts= 5.5

s) and f=16.7 Hz

6 ms9 ms

15 ms

21 ms

24 ms

30 ms

42 ms

Ktf,ψmax

Tp [ms]

36 ms

tal

12 ms

18 ms

27 ms

33 ms

39 ms

= 0.1° (Ts = 5.5 s) , f = 16.7 Hz

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

61869-2 ed. 1 © IEC 38/404/CDV - 64 -

Range 2: max,max, tfpaltf ttt <≤ 1881

The second time range continues with the envelope curve tfpK for °= 90γ which leads to the 1882

highest peak flux, therefore ϕθ −°= 90 . 1883

1/)sin(//)cos( +

−+

−−

−

−= ⎟

⎠⎞⎜

⎝⎛ sTtesTtepTt

esTpTpTsT

tfpK θθω

(6)

1884 up to the curve maximum at the time 1885 1886

)cos(

)sin(2)cos(

lnmax, θ

θω

θsT

pTsT

sT

pT

sTpT

sTpTtfpt

−+

−=

(7)

1887 1888 Range 3: altfp tt ≤max, 1889

The third time range continues with the constant maximum max,tfpK given in eqn. (8) for higher 1890 accuracy limit times. 1891 1892 1893

1)cos(

)sin(2)cos(

)sin()cos(max, +

−−+

⋅+

+=

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛

pTsTpT

sT

pTsT

sT

pT

sT

sTpTpTtfpK

θ

θω

θ

θθω (8)

1894 1895 1896 1897

B.1.3 Duty cycles 1898

The transient dimensioning for autoreclosure duty cycles has to be done separately for each 1899 cycle according to the equations given above. 1900 1901 Gapped cores 1902 For gapped cores the magnetic flux and therefore the transient factor declines exponentially 1903 with secondary time constant sT (which changes with the actual operational burden) during 1904 the open time. 1905

)()'( "/)(, altd

TttdCOCtd tKetKK sfr +⋅= −

−− (9) Nongapped Cores 1906 For nongapped cores remanence is possible and there is no significant flux declination in the 1907 worst case. 1908

)()'( ")(, altdtdCOCtd tKtKK +=−− (10)

1909

61869-2 ed. 1 © IEC 38/404/CDV - 65 -

1910

1911

B.2 Determination of the magnetizing characteristic 1912 of protective current transformers for transient performance 1913

1914 1915 1916

B.2.1 General 1917

Measuring the core magnetization characteristic implies establishing the relationship between 1918 the core secondary linking flux and magnetizing current. 1919 1920 If an arbitrary voltage u(t) is applied to the secondary terminals (see figure 2B.13), the core 1921 flux ψ(t) linked through the secondary winding at time t is related to this voltage through the 1922 equation: 1923 1924

∫ ⋅−=t

mct dttiRtut0

))()(()(ψ (11) 1925

1926 The methods described in the following clauses take advantage of this relationship. 1927 1928

im Rct

u(t)

1929 Fig. 2B.13: Basic circuit 1930

1931 1932 For TPX current transformers it is necessary to demagnetize the core before each test, 1933 because of the high remanence factor. For TPY current transformers the remanent flux is 1934 often so low that it can be neglected. Demagnetization requires additional means by which the 1935 core can be subjected to slowly decreasing hysteresis loops starting from saturation. A direct 1936 current source will normally be provided when the d.c. test method has to be used. 1937 1938 1939 The a.c. method or d.c. method may be applied. 1940 While the a.c. measuring method is easier to apply, it may lead to high voltages, and to too 1941 high remanence flux values due to additional eddy currents. 1942 1943 1944 1945

B.2.2 A.C. method 1946

A substantially sinusoidal a.c. voltage u(t) is applied to the secondary terminals. The test may 1947 be performed at reduced frequency f’ to avoid unacceptable voltage stressing of the winding 1948 and secondary terminals. 1949 1950

61869-2 ed. 1 © IEC 38/404/CDV - 66 -

1951 1952

The knee point shall be determined according to 7.3.5.205.1. 1953 1954 The magnetising inductance Lm shall be determined by measuring the secondary inductance 1955 between 20% and 90% of knee point e.m.f. Ek as follows (i20 and i90 are peak values of the 1956 magnetizing current values at the appropriate percentages of Ek): 1957 1958

'2*)(

7.0

2090 fiiEL k

m π−= (12) 1959

1960 1961

In determining the remanence factor Kr by the a.c. test method, it is necessary to integrate the 1962 exciting voltage according to equation (11). The integrated voltage with the corresponding 1963 current im will display a hysteresis loop, showing the saturation flux ψs. The flux value at zero 1964 crossing of current is deemed to represent the remanent flux ψr. The remanence factor Kr is 1965 then calculated according to 3.4.211 as 1966 1967

s

rrK

ψψ

= (13) 1968

1969 At lower frequencies, effects of undue eddy current losses in the core and capacitive currents between 1970 the winding layers will be less likely to cause false readings. 1971 1972 1973

1974 Fig. 2B.14: Determination of remanence factor by hysteresis loop 1975

1976 1977 1978

B.2.3 D.C. method 1979

1980 The d.c. saturation method uses a d.c. voltage u(t) of such duration that saturation flux is 1981 reached. The flux measurement is derived according to equation (11), where u(t) is the 1982 voltage across the terminals. 1983

1984

61869-2 ed. 1 © IEC 38/404/CDV - 67 -

Fig. 2B.15: Circuit for d.c. method 1985

1986 The applied voltage source shall be suitable to reach saturation. 1987 1988 The discharge resistor Rd shall be connected, as otherwise the core inductance may cause 1989 very high overvoltages when switch S is opened and the inductive current interrupted. 1990 1991 Some time after the switch S has been closed, the exciting current im will be deemed to have 1992 reached its maximum value (Im) at which the core flux would remain constant. 1993 1994 The rising values of the magnetizing current and of the flux shall be recorded up to the time at 1995 which the values become constant, then the switch S will be opened. 1996 1997 Typical test records of the flux ψ(t) and of the magnetizing current im(t) are shown in figure 1998 2B.16. 1999 2000 2001

imψ

t

im

ψ

ψ

im

From oscillograph From X-Y recorder

2002 Fig. 2B.16: Typical records 2003

2004 The magnetizing inductance (Lm) may be deduced according the following equation: 2005 2006

2090

7.0ii

L sm −

=ψ

(14) 2007

2008 where i90 and i20 are magnetizing current values at the appropriate percentages of ψs. 2009 2010 2011 At the opening of switch S, a decreasing magnetization current flows through the secondary 2012 winding and the discharging resistor Rd . The corresponding flux value decreases, but may 2013 not fall to zero at zero current. When a suitable exciting current im has been chosen to 2014 achieve the saturation flux ψs, the remaining flux value at the zero current shall be deemed to 2015 be the remanent flux ψr. 2016 2017 For TPY current transformers the remanence factor Kr is determined 2018

s

rrK

ψψ

= (15) 2019

2020 For a TPY current transformer whose core has not been demagnetized before, the remanence 2021 factor (Kr) may be determined by an additional test in which the secondary terminals have 2022 been interchanged. In this case, the remanence factor Kr may be calculated as above, but 2023 assuming for ψ the halved value of the remanent flux measured in the second test. 2024 2025 2026 2027

61869-2 ed. 1 © IEC 38/404/CDV - 68 -

2028

B.2.4 Capacitor discharge method 2029

2030 The capacitor discharge method uses the charge of a capacitor for energizing the current 2031 transformer core from the secondary. The capacitor is charged with a voltage sufficiently 2032 high to produce saturation flux. 2033 2034 2035 2036 2037

2038 Fig. 2B.17: Circuit for capacitor discharge method 2039

2040 2041 2042 The derivation of the magnetizing inductance (Lm) and of the remanence factor Kr is 2043 identical with the method given B2.3 (d.c. method). 2044 2045 2046

sψrψ

rK =

2047 Fig. 2B.18: Typical records for capacitor discharge method 2048

2049 2050

61869-2 ed. 1 © IEC 38/404/CDV - 69 -

2051 2052

2053

B.3 Determination of the error at limiting conditions 2054 of protective current transformers for transient performance 2055

B.3.1 General 2056

2057 The instantaneous error current can be measured in different ways. In all cases, the errors of 2058 the measuring system shall not exceed 10 % of the error limit corresponding to the class of 2059 the tested CT during the whole of the duty cycle. 2060 2061

B.3.2 Direct test 2062

Class TPX current transformers should be demagnetized before the direct test because of the 2063 high remanence factor. It may be necessary to demagnetize class TPY current transformers if 2064 the remanence factor Kr is not negligible. 2065 2066 Two direct tests are performed at rated frequency and with rated secondary burden: 2067 2068 a) 2069 The rated primary short-circuit current at rated frequency is applied without any offset. The 2070 a.c. component of the total error is measured and shall be in accordance with the theoretical 2071 value 1/ωTs. 2072 2073 2074 b) 2075 The rated primary short-circuit current at rated frequency is applied with the required offset. 2076 For specified values of primary time constant up to 80 ms, the test is performed in the 2077 specified accuracy limiting condition (specified duty cycle). The primary time constant shall 2078 not deviate by more than 10 % from the specified value. 2079 2080 For specified values of primary time constant above 80 ms, the tests can be performed in 2081 equivalent accuracy limiting conditions (by modifiing duty cycle and/or burden), subjected to 2082 agreement between user and manufacturer. 2083 2084 During the energization period, the first peak of the primary current shall be not less than the 2085 value corresponding to the specified conditions. 2086 2087 The secondary linked flux shall be recorded. The error in flux measurement shall not exceed 5 %. 2088 2089

dtiRR

RRtt

sbb

bct ∫ ⋅⋅+

=Ψ0

)( 2090

2091 2092 For class TPX and TPY current transformers, the instantaneous error current iε is measured 2093 as prs ikii −⋅=ε . The error value ε shall be determined according to 3.4.602. Its value shall 2094 not exceed the limit given in table 1. 2095 2096 For class TPZ current transformer, the a.c. component of the error current is measured as one 2097 half of the peak-to-peak value (see figure 2B.19). The error value acε shall be determined 2098 according to 3.4.603. Its value shall not exceed the limit given in table 206. 2099 2100 Note: It is possible that the class definition does not contain a duty cycle. 2101

61869-2 ed. 1 © IEC 38/404/CDV - 70 -

In this case, for test purposes, a duty cycle leading to the given Ktd value shall be agreed between user and 2102 manufacturer. 2103 2104 2105 2106

2bii:TPZFor ci:TPYFor

iici2bia

εaceε

εdcεacεacεdc

===

+===

εi

2107 2108

Fig. 2B.19: Measurement of error currents 2109

2110 2111 2112

B.3.3 Indirect test 2113

2114

B.3.3.1 Limits of exciting secondary current (Îal) 2115

2116 2117 For TPX and TPY current transformers, the peak value of the exciting secondary current (Îal) shall not 2118 exceed the value given below: 2119 2120

%100[%]ˆ

2 ε⋅⋅⋅≤ sscsnal KII

) 2121

2122 For TPZ current transformers, the a.c. peak value of the exciting secondary 2123 current (Îal) shall not exceed the value given below: 2124 2125

⎟⎟⎠

⎞⎜⎜⎝

⎛+

−⋅⋅⋅≤

%100[%]ˆ12 ac

S

tdsscsnal T

KKII εω

) 2126

2127 NOTE - For TPZ current transformers the accuracy is specified only for the a.c. component while, in the 2128 determination of the permissible value of Ial during indirect tests, it is necessary to take into account also 2129 the d.c. component of the exciting current. In the above equation, the d.c. component is represented by 2130 (Ktd – 1) and the permissible error in the a.c. component by 0.1 . 2131 2132 2133 2134

B.3.3.2 A.C. method 2135

2136

61869-2 ed. 1 © IEC 38/404/CDV - 71 -

The a.c. method shall be applied according to annex B.2.2 2137 2138 The voltage shall be increased up to Ual. The appropriate excitation current Îal shall not 2139 exceed the limit given in annex B.3.3.1 2140

2141

The magnetic flux at accuracy limiting condition is given by 2142

ωal

alU⋅

=Ψ2

2143

2144

2145

B.3.3.3 D.C. method and capacitor discharge method 2146

2147 2148 The d.c. method shall be applied according to annex B.2.3. 2149 2150 The magnetic flux )(tΨ and the exciting current im (t) shall be recorded. 2151

At a magnetic flux at accuracy limiting condition 2152 2153 2154

ω)(2 ctbsnssctd

alRRIKK +⋅⋅⋅⋅

=Ψ 2155

2156 the appropriate value of the exciting current Îal shall be determined. This value shall not exceed the 2157 limit given in B.3.3.1. 2158 2159 2160

B.3.3.4 Determination of Fc 2161

2162 According to the definition of Fc, the flux values at error limiting condition in direct and indirect 2163 test have to be determined for the same value of magnetizing current. 2164 2165 In the first step, the magnetic flux ψdir shall be determined in the direct test as the peak value 2166 of the relevant flux within the duty cycle. The appropriate error current Iεd shall also be 2167 measured. 2168 2169 The magnetic flux ψind is determined in a indirect test as the flux corresponding to a 2170 magnetizing current equal to Iεd 2171 2172

Fc may now be calculated as dir

indcF

ΨΨ

= 2173

2174

61869-2 ed. 1 © IEC 38/404/CDV - 72 -

2175

B.4 Alternative measurement of the steady state ratio error 2176

2177 For low leakage reactance current transformers, the following indirect test will lead to results 2178 which are very close to the results obtained in the direct test. 2179 2180 Nevertheless, routine tests for steady state ratio error determination shall always be 2181 performed as a direct test, as this method gives the highest evidence of the “low leakage 2182 reactance property” of a core, including magnetic “homogenousness” of the iron core. On the 2183 other hand, the alternative method is suitable for on-site measurements, and for monitoring purposes. 2184 In this case, it shall be noted that this method never considers the influence of current flow in the 2185 neighbourhood of the current transformer. 2186 2187 2188 2189 2190 2191 2192 For the determination of the ratio error the following simplified equivalent circuit diagram is 2193 used: 2194

2195 Fig. 2B.20 Simplified equivalent circuit of the current transformer 2196

2197

A substantially sinusoidal voltage is applied to the secondary terminals S1 – S2 of the CT. The 2198 test voltage across the terminals Us Test and the current Is Test are measured. The injected 2199 voltage should generate an e.m.f. across the main inductivity with the same amplitude than 2200 during operation with a certain current and the actual burden. The e.m.f. can be calculated 2201 from the test results by subtracting the voltage drop across the winding resistance RCT from 2202 the test voltage Us Test across the S1 – S2 terminals. This subtraction has to be done in the 2203 complex plane. The measured current Is Test is equal the error current Ie. 2204

The ratio error can be expressed as: 2205

2206

1−=

−

=snp

pns

pn

snp

pn

snps

IIII

III

IIII

errorRatio [1] 2207

With: 2208

( )p

ssepse

s

pp

NNIIIII

NNI +

=⇒+= [2] 2209

θ

Ip*Np/Ns= Is+ Ie

E0

61869-2 ed. 1 © IEC 38/404/CDV - 73 -

the ratio error can be expressed as: 2210

( ) 1−+

=snsse

pnps

INIIINI

errorRatio [3] 2211

2212

2213

To determine the ratio error for a certain secondary current Is the following test procedure is 2214 proposed: 2215

2216

• Calculation of the secondary voltage across S1 – S2: 2217

( )bbss jXRIU += 2218

• Measurement of the secondary winding resistance R (value at the actual temperature) 2219

• Calculation of the corresponding e.m.f. ******** R, not Rct 2220

scts URIE +=0 2221

• Injection of 2222

ctTestsTests RIEU += 0 ( with Is Test = Is) 2223

into the secondary terminals S1 – S2 2224

• Measurement of the voltage Up Test across P1 - P2 2225

• Calculation of the turns ratio 2226

0E

UNN Testp

s

p = 2227

• Calculation of the corresponding Ip 2228 2229

p

sTestssP N

NIII

)( += 2230

2231 The ratio error can be calculated as: 2232 2233

( ) 1−+

=snssTests

pnps

INIIINI

errorRatio 2234

2235 2236 2237 2238

61869-2 ed. 1 © IEC 38/404/CDV - 74 -

Annex C 2239 Technique used in temperature rise test of oil-immersed transformers 2240

to determine the thermal constant by an experimental estimation 2241 (informative) 2242

2243

List of symbols: 2244

θ Temperature in °C 2245

θ(t) Oil temperature, varying with time (this may be top oil, or average oil) 2246

θa External cooling medium temperature (ambient air or water) assumed to be 2247 constant 2248

∆θ Oil temperature rise above θa 2249

θu, ∆θu Ultimate values in steady state 2250

ε(t) Remaining deviation from steady-state value θu 2251 To Time constant for exponential variation of bulk oil temperature rise 2252 h Time interval between readings 2253

θ1, θ2, θ3 Three successive temperature readings with time interval h between them. 2254

In principle, the test should continue until the steady-state temperature rise (of the oil) is 2255 ascertained. 2256

θu = θa + ∆θu (1) 2257

θ(t) = θa + ∆θu (1 et/To) (2) 2258

The remaining deviation from steady state is then: 2259

ε(t) = θu θ(t) = ∆θu x et/To (3) 2260 It is considered that: 2261

- the ambient temperature is kept as constant as possible 2262

- the oil temperature θ(t) will approach an ultimate value θu along an 2263 exponential function with a time constant of To. 2264

- The equation 2 is a good approximation of the temperature curve (see fig.2B.1) 2265

Given three successive readings ∆θ1, ∆θ2 and ∆θ3, if the exponential relation of equation (2), 2266 is a good approximation of the temperature curve, then the increments will have the following 2267 relation: 2268

oh/T

23

12 eθθ

θθ=

∆−∆

∆−∆ 2269

23

12o

θθ

θθln

∆−∆

∆−∆=

hT (4) 2270

The readings also permit a prediction of the final temperature rise: 2271

( )

312

312u θθθ

θθθθ

∆−∆−∆

∆∆−∆=∆

2

2

(5) 2272

61869-2 ed. 1 © IEC 38/404/CDV - 75 -

Successive estimates are to be made and they should converge. In order to avoid large 2273 random numerical errors the time interval h should be approximately To and ∆θ3/∆θu should 2274 be not less than 0,95. 2275

A more accurate value of steady-rate temperature rise is obtained by a least square method 2276 of extrapolation of all measured points above approximately 60 % of ∆θu (∆θu estimated by the 2277 three point method). 2278

A different numerical formulation is: 2279

( ) ( )

23

12

23122u

θθ

θθln

θθθθθθ

∆−∆

∆−∆

∆−∆−∆−∆+∆=∆ (6) 2280

2281

2282

Figure 2C.1 - Graphical extrapolation to ultimate temperature rise 2283

61869-2 ed. 1 © IEC 38/404/CDV - 76 -

Annex D 2284 Determination of the turns ratio error (informative) 2285

2286 The actual transformation ratio is affected by errors from three sources: 2287

a) the difference between the turns ratio and the rated transformation ratio 2288

b) the core excitation current (Ie) 2289

c) the currents which flow in the stray capacitances associated with the windings. 2290 2291 In most cases, it is reasonable to assume that for a given secondary winding induced e.m.f. 2292 (Es), the error currents due to stray capacitances and core magnetization will maintain a 2293 constant value irrespective of the value of the primary energizing current. Es can theoretically 2294 be maintained at a constant value for a range of energizing currents, provided that the 2295 secondary loop impedance can be appropriately adjusted. For current transformers designed 2296 to be of the low leakage reactance type, the secondary leakage reactance can be ignored and 2297 only the secondary winding resistance has to be considered. Thus, for any two currents l's 2298 and I"s the basic equation defining the test requirement is 2299 given by 2300 2301

)''('')'(' bSSbS RRIERRI +==+ 2302 2303 where R is the actual resistance of the secondary winding. 2304 2305 2306 Assuming that the measured ratio errors are ε’c and ε’’c , the turns ratio error is denoted as εt, 2307 and the combined magnetization and stray currents are given by Ix. The respective error 2308 currents will be given by: 2309

100'')''(

100')'( sn

tCXsn

tCIKIIK

⋅−==⋅− εεεε 2310

whence: 2311 - 2312

SS

SCSCt II

II'''

''''''−

⋅−⋅=

εεε 2313

2314 2315 If I’S = 2I’’S, the turns ratio error is given by 2 ε’c – ε’’c. 2316 A test at rated current with minimum secondary connected burden, followed by a test at half 2317 rated current and suitable increase in secondary loop resistance, will usually give satisfactory 2318 results. 2319 2320

Resumen Cei 61869

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