101413081 Surge Arrester Presentation

7/30/2019 101413081 Surge Arrester Presentation

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These were previously called Lightning arresters,which is not the correct name or definition.

Surge arrester is a device which protects the electricalexpensive items from damage; like Transformers orReactors or other insulators.


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Expulsion Type.

Gap Type.

Metal oxide Type


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These are also called Non linear resistance typearresters.

Normally Aluminum oxide is used for Metal oxide

because it is cheap and have good characteristics.Due to non linear voltage / current characteristicsit offers low resistance path to the flow of highdischarge current thus limiting the voltage acrossthe arrester terminals.


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It is the maximum permissible voltage which thearrester can withstand, without discharge and without

changing its operating characteristics.


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The voltage which appears across the terminal ofarrester during discharge. The minimum, the better.

The following types of residual voltages are ofimportance.


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Switching impulse residual voltage

It is equipment insulation withstand test voltage with a

front time larger than 30 s.

Lightning impulse residual voltage

It is 1.2/50 s wave shape.

BS use current wave of form 8/20 s for residual voltage.

The above are referred to Arrester Currents.


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TheArrester must be selected with a rated voltagehigh enough towithstand temporary over voltageswhich may be produced by various occurances. Line tofault current is the most common occurance


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There should be sufficient margin between variousrequired impulse and Power frequency withstandvoltages and arrester voltage. It is margin in % and

expressed as:(Insulation withstand voltage Residual voltage) x 100

Residual voltage


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It is the capability of arrester to dissipate a givenamount of energy without damage.


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The ability of arrester to conduct short circuit current

without violent disintegration in the event of itsfailure.


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1. Highest system voltage is the base for Designparameters. It is defined by IEC and otherStandards

2. Temporary over voltages in the system arenormally determined by single line to groundfault.

As such Rated voltage will be differentdepending on the grounding conditionand protection scheme. In case of directlygrounded system the voltage of healthyphase may rise 1.4 times phase to earth voltage.


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where 1.4 is the Earth factor.

3. In case of ungrounded system Earth factor will

be 1.73. Thus the voltage may rise upto 1.73 timesthe phase to Earth voltage.


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3. Check for the abnormal operating conditions,Um.

4. Determine continuous operating voltage (COV)

COV =Um/35. Determine Preliminary rated voltage VR0 based

on COV

6. VR0 = COV/K0 where K0 is Design factor


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6. Determine Temporary over voltage at Earth faultTOVE = KE x COV

7. Select Preliminary Rated Voltage RE based onTOV

E

Determine Rated voltage, RE = TOVE / KT ,where KT isarrester TOV capability expressed as multiple of rated

voltage.


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The following Tests are made on Arresters

Routine Tests1. Power Frequency voltage spark over test on

complete arrester2. Lightning voltage impulse spark over test on

complete arresterVisual examination

3. Residual voltage Test (if agreed between Client andmanufacturer)


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1. Power Frequency Voltage spark over voltage

2. Lightning voltage impulse spark over voltage

3. Switching voltage impulse spark over voltage

4. Spark over voltage/Time curve test5. Residual voltage test


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6. Operating duty

7. Pressure relief test


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System Voltage

Nom./Highest

Arrester Rated

Voltage

Max.Contin-uous

Operating

voltage.

Virtual

Steepness of

Front for Front of

wave

Max. Front of

wave S.O.V

Max. Residual

Voltage

KV KV KV KV (Peak) KV (Peak) KV (Peak)11/12 12 10 100 50 43

66 /72.5 60 46 500 250 216

132/145 120 92 930 463 400

220/245 198 156 1200 746 649


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System Voltage

Nom./Highest

Arrester Rated

Voltage

Max.Contin-uous

Operating

voltage.

Steep current (at

10 KA) 1/20 s

impulse residual

voltage

Lightrning current

(at 10 KA) 8/20

impulse residual

voltage

Switching current

(at 0.5/1KA)

30/60 residual

voltage

KV KV KV KV (Peak) KV (Peak) KV (Peak)

11/12 12 10 40 38 27

66 /72.5 60 46 175 160 130

132/145 120 92 330 295 250

220/245 198 156 545 485 410


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Normal System

Voltage132 KV

Max. system

Voltage, Vmax ==1.1* Vnom KV

= 145 KV

Continuous

operating voltage,

C.O.V

145/1.732 = 84 KV

Earth Factor, KE =1.4

T.O.V == KE * COV


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Assume a working on 132 KV protected by a Surge arrester 25 Meters from Transformer.

Assume velocity, V = 300 m / s

Steepness of Incoming wave =1000 KV/s

Residual voltage, U1 = 276 KV

Voltage Stress, V2 = =276+2*1000*25/300 KV

= 443 KV

BIL of 132 KV System = 650 KV

Margin= =(650-443)/443*100

=47 %

101413081 Surge Arrester Presentation

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