Matz 5

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Dynamic testing of on-load tap changer switching

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On-load Tap Changer Designs

A typical diverter switch type OLTC showing both tap selector switch and diverter switch (MR)

A typical OLTC with selector switch (17 taps linear) (ABB)

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WRM/tap, diverter design Old/aged condition

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WRM/tap , selector type OLTC As new

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Dynamic measurements during tap switching

Continuity/break-before-make testing Shut-off if current path is interrupted

Current change detection

Dynamic measurements (DRM) Dynamic current/ripple

Dynamic voltage

Dynamic resistance

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Considerations/issues when performing dynamic testing

Transformer winding inductance is not constant Low or high test current (saturation or not)

Open or shorted secondary (assuming LTC on primary)

Measurement data is pending power source Constant current source

Constant voltage source

Source impedance

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Dynamic current measurements at different test curr ent30 MVA, YNyn0, open LV

20A, 38% current drop 10A, 27% current drop


AM Forum workshop, Madrid 2011

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Dynamic current measurements at different test curr ent30 MVA, YNyn0, shorted LV



AM Forum workshop, Madrid 2011

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Dynamic Resistance Measurements on a load tap-changer (direct method)

TM1800/1700/1600/EGIL(CBA)

LTC135 (PS)

DC test current

DC test currentLV windings shorted

Computer for detailed

analysis and reporting

Measure test current and voltage over the winding

Calculate R (source impedance >> resistor value)

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Tap transition Selector + diverter typ LTC

Typical LTC sequence of events when tap is switched from one position to next.

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Tap transition - Selector switch LTC

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OLTC DRM measurements, Uppsala

Transformer data: 20 MVA, 20/10 kV, YNyn, (spare unit in good condition) OLTC on HV with 17 taps (selector switch type LTC)

Test equipment: TM1800 CB-DRM analyzer

Multi-channel voltage and current measurements OLTC control Static and dynamic resistance measurements

LTC135 DC source for load-tap changer testing 48 V compliance voltage 1 x 5A (10 output impedance) 3 x 1A (48 output impedance) 3 x 0.1A (480 output impedance) Safe discharge of windings after measurement

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DRM with LV shorted

DRM with constant current source

Blue Voltage/Resistance, Red Test current.

H1 1-2 tap change with LV shorted.

Transition times and resistor values easily recognized

Resistance

Time

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Transition time measurements

H1 OLTC transition times. 1-2 to 16-17 tap change (ms)

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Resistor values, H1

R1 and R2 transition resistance values per tap (value/10). All within spec ( 10%)

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Static and Dynamic Resistance Measurements on a load tap-changer in one operation (patent pending)

TM1800/1700/1600/EGIL(CBA)

LTC135 (PS)

DC test current

DC test current

LV windings NOT shorted!

Computer for detailed

analysis and reporting

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Dynamic measurements, current (5A) + HV and LV voltage - 20 MVA, YNyn0, open LV

R1 and R2 transition resistor values per tap (value/10). All within spec ( 10%)

Current

HV voltage

LV voltage

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Dynamic analysis, utilizing new method (patent pending) for calculating resistance

LV voltage

HV voltage

Resistance

Test current

T1 70 msT1//2 8 msT2 56 msTswitch 134 msRwinding 0.52 R1 2.94 R// 1.42 R2 2.83

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OLTC DRM measurements, Stockholm

Transformer data: ASEA-Lepper 6 MVA, 21/11 kV, Dyn11, 1973 OLTC ASEA ASEA UZEDT , 17 taps




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Dynamic analysis, ASEA Lepper 6 MVA with LTC ASEA UZEDT, start time

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Dynamic analysis, ASEA Lepper 6 MVA with LTC ASEA UZEDT, switch time

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Dynamic analysis, ASEA Lepper 6 MVA with LTC ASEA UZEDT, start time

0

500

1000

1500

2000

2500

3000

Start time, ms

Start time, ms

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Dynamic analysis, ASEA Lepper 6 MVA with LTC ASEA UZEDT, switch time

0

10

20

30

40

50

60

R1 time, ms

R// time, ms

R2 time, ms

Total swithc time, ms

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OLTC DRM measurements, Belgrade

Transformer data: ELTA 16 MVA, 110/36.75/10.5 kV, YNynd5, 1973 OLTC ELIN on HV with 27 taps (23 effective)




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ELTA, tap 1-7, up

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ELTA, tap 4-5 transition, 1A

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ELTA, tap 2-3 transition, 1A

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Summary and conclusions A CB analyzer/signal recorder with analog inputs together with suitable power supply is a

good tool for performing various DRM measurements e.g. on load tap-changers To measure dynamic properties in a tap changer (HV), several methods are possible:

Measure dynamic current/ripple on primary with a const ant voltage source and secondary open Current drop value is strongly pending test current/winding inductance and can only be used as fingerprint Contact switching/timing may be measured (difficult) Diverter resistor values cannot be measured

Measure dynamic current/ripple on primary with a const ant voltage source and secondary short-circuited

Current drop value is slightly pending test current/winding inductance Contact switching/timing can be measured Diverter resistor values cannot be measured

Measure dynamic resistance on primary with a constant current source and secondary short-circuited

Contact switching/timing can be measured Actual diverter resistor values can be measured (high impedance source)

Measure dynamic voltage on secondary Contact switching/timing can be measured Actual diverter resistor values cannot be measured

Measure dynamic resistance by measuring dynamic voltage on primary and secondary windings Contact switching/timing can be measured Actual diverter resistor values can be measured (patent pending)

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Matz 5