Partial Discharge and Tan Delta On-Site Diagnostic … ICC Educational Program Fall 2000. Partial...
Transcript of Partial Discharge and Tan Delta On-Site Diagnostic … ICC Educational Program Fall 2000. Partial...
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ICC Educational Program Fall 2000.
Partial Discharge and Tan Delta On-Site Diagnostic Testing of
extruded cable with the integrated PD and TD BAUR
VLF test instrument. By:
Craig Goodwin, HV Diagnostics Inc. GA, USAe-mail: [email protected]
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ICC Educational Program Fall 2000.
Summary of Presentation
• Theory / Background
• Description of Methods used
• Field Examples
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ICC Educational Program Fall 2000.Two Main Groups of On-Site Cable Diagnostics Test EquipmentGroup 1:
• On Line (In Service)
• Off Line (out of service).
Group 2:
• Global / Integral Assessment Diagnostics eg. TD.
• Discrete Location Diagnostics eg. PD
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ICC Educational Program Fall 2000.Why use Alternating Field instead of DC for HV Cable
Testing?Why not DC ?• Potentially damaging to aged extruded cable. • Only able to detect gross / major insulation defects. • No further internal Partial Discharges after DC threshold.
Example: 10-kV-XLPE-cable, with penetrated needle remaining insulation thickness approx. 0,8 mm breakdown higher than 12Vo.
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ICC Educational Program Fall 2000.
Benefits of Voltage Testing with VLF Sinusoidal Waveforms in the
field. Pure sinusoidal, load independent alternating
voltage without any DC offsets. Low Power requirement Generally Higher PD inception voltage High electrical tree growth rate Compact portable design of test equipment Easier to integrate Cable diagnostic interfaces
such as TD and PD.
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ICC Educational Program Fall 2000.
PD- inception voltage levels for different test voltage waveforms on XLPE
Reference:Research and Development, Annual Report 1992, TU BerlinHigh Voltage InstituteProf.Dr.-Ing.Kalkner, Dipl.Ing.R.Bach"Investigation on site test methods of M.V.cables with different H.V.waveforms"
50 Hz 0,1 Hz cos-rectangular
0,1 Hz sin. osc.wave0
5
10
15
20
25
30
35
40
50 Hz 0,1 Hz cos-rectangular
0,1 Hz sin. osc.wave
wetdry
PD-I
ncep
tion
Volta
ge [k
V]
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ICC Educational Program Fall 2000.Electrical Tree Growth Rate from PD -
Needle Point Fault.Applied Voltage: 3V0 using Various
Waveforms
50 Hz 0,1 Hz cos-rectangular
0,1 Hz sin0
2
4
6
8
10
12
14
elec
tric
al tr
ee g
row
th ra
te [m
m/h
]
50 Hz 0,1 Hz cos-rectangular
0,1 Hz sin
dry, newwet, service aged
Reference:Research and Development, Annual Report 1992, TU BerlinHigh Voltage InstituteProf.Dr.-Ing.Kalkner, Dipl.Ing.R.Bach
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ICC Educational Program Fall 2000.
European Union Standard for Cable Maintenance High Voltage Tests: CENELEC
HD 620 S1 1)
Cables from 6 to 36 kVFrequency Test voltage Testing time
PE/XLPE cables 0,1 Hz 3 x Uo 1 hour
50 Hz 2 x Uo 1 hour
For Paper insulated mass impregnated cables CENELEC HD 621:
DC test or above mentioned parameters1) June 1996, 15 EUcoutries
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ICC Educational Program Fall 2000.
"WATER TREEING" in polymeric insulation(schematic layout)
electrical field conditions for possible water development of disturbance field "water trees" time
outer semiconductinglayer
insulation
inner semiconductinglayer
conductor
"bow-tie trees"
"vented trees"
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ICC Educational Program Fall 2000.
Vented- tree growing from the inner semicon layer of a 30 kV- PE- cable
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ICC Educational Program Fall 2000.
Dielectric Failure of insulation originating from a water tree
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ICC Educational Program Fall 2000.
Comparison of Electrical and Water treeingElectrical Treeing (ET): high localized field fast tree growth in PE or XLPE insulation accompanied by partial discharges long channel structures (visible trees) clear indication of an electrical breakdown
Water Treeing (WT): can be present even at small electric field
strengths (e.g. < 1 kV / mm) extremely slow tree growth (e.g. over 6-10 years) no partial discharge associated.
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What is Dissipation Factor ( tan
time/sec0 10
voltage
current
= U RU C
²/².
1CR.
dissipation factor tan = true power reactive power
=
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ICC Educational Program Fall 2000.
Simplified Dielectric Equivalent Circuit of a Water Tree
w t
R1C1
R2 C2
>>
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ICC Educational Program Fall 2000.
Voltage Dependence of 0,1 Hz Dissipation Factor of New and Service-aged XLPE-insulated Medium Voltage
Cablestan . 10-3
0
1
2
3
4
5
6
7
0 0,5 1 1,5 2 2,5 3
U / U 0
0,1
Hz
diss
ipat
ion
fact
orreference cable (new)slightly service-aged (1)moderately service-aged (2)moderately service-aged (3)strongly service-aged (4)
JICABLE, Versailles, June 1995, paper B.9.6.
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ICC Educational Program Fall 2000.
Field Test Result for an 1974 XLPE Cable
Good Resultfor an old Cable.
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ICC Educational Program Fall 2000.
Conclusions of TD Diagnostics A TD cable assessment system can clearly distinguish
between new, medium and strongly aged extruded cable insulation.
Water trees which are a major original source of insulation failures in aged extruded cables can be detected in a non-destructive manner.
The TD cable assessment system provide reliable results in field use for both extruded and PILC cables.
To detect singular defects, a combined assessment system including the application of partial discharge measurement and location in addition to TD is necessary.
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ICC Educational Program Fall 2000.
0.1 Hz Partial Discharge 0.1 Hz Partial Discharge TestingTesting
• Measurement of partial discharge activity at siteincluding calibration
• Precise PD cable fault location
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ICC Educational Program Fall 2000.
Principle of P.D. Location using TDRTechniques:
560 m
339,8 m
180,4 m
joint with PD fault (1)
t
t
near cable end
partial discharge fault (2)
far cable end
impulse reflected via far cable end (2)
impulse directly reflected first reflection (2)
impulse directly reflected (2)
impulse directly reflected first reflection (1)
impulse reflected via far cable end (1)
impulse directly reflected (1)
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ICC Educational Program Fall 2000.
TD and PD: A good combination of Diagnostic Methods:
• Dielectric Dissipation Factor (TD) Measurement:Overall assessment of the cable insulation.Non-destructive test method
•Partial Discharge Measurement:Discrete Location of PD in cables, accessories and terminations.
•Dielectric Withstand Test (“Hi Pot”):High Voltage Acceptance or Maintenance Dielectric testing
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ICC Educational Program Fall 2000.
Example of PD Location on XLPE Cable.
Nominal OperatingVoltage: Vo = 14kV
PDIV: only at 19kV
Note: TD values are poor even at Vo.