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Power transformer testing
Power Transformer Factory Test using IEEE Standards Waldemar Ziomek CG Power Systems Canada
IEEE Training, Houston, Texas, Oct.8-9, 2014
Power transformer testing 2
Power Transformer Factory test
- Objective of tests
- Classification of tests
- List of tests
- Connections for test
- Details of Tests
- Sequence of tests
- Future trends Topics covered
Tests for special transformers, such as HVDC converter
or Phase shifting transformers are not covered
Power transformer testing
Objective of testing
- Compliance to applicable standards
- Compliance to customer specification
- Verify guaranteed parameters
- Assess quality and reliability
- Verify design
- Obtain additional performance and reference data 3
Power transformer testing
Classification of tests
- Routine test
- Design test
- Other tests
As per IEEE standards
As per characteristic of test
- Quality verification tests
- Performance tests
- Thermal tests
- Dielectric tests
- Mechanical tests
- Test data for future reference
- Others 4
Routine Design Others Remark No load loss and excitation current X X Performance test LTC operation with no load voltage (cycle recording) X Quality verification Impedance voltage and load loss X Performance test LTC operation at load current (cycle recording) X Quality verification Zero phase sequence voltage X Future/System reference Temperature rise X X Thermal and performance List of tests 7 8 Dielectric tests Routine Design Others Remark Lightning impulse X X Dielectric test Switching impulse X Dielectric test Applied voltage test X Dielectric test Induced voltage with or without partial discharge measurement X Dielectric test No load loss after dielectrics X CSA Low or Power frequency test on auxiliary / control devices and current transformers X Dielectric test List of tests
Routine Design Others Remark Audible sound level X Performance Short circuit capability X Performance and quality test Operation tests of all devices X Quality verification Dissolved gas in oil analysis X Quality, Thermal, Future reference Lifting and moving devices X Mechanical test Pressure X Mechanical test Leak X Quality verification List of tests 9 Test system accuracy requirement
Quality measured Accuracy
Losses +/-3%
Voltage +/-0.5%
Current +/-0.5%
Resistance +/-0.5%
Temperature +/-1.0degC
Frequency of test source to be within +/-0.5%
of rated frequency
10
Equivalent circuit on open circuit connection 13 Short circuit connection
- Impedance and load loss
- Temperature rise 14
Measurement of impedance and load loss 15 Equivalent circuit on short circuit connection 16
Insulation types
19
Insulation stressed by different tests
20
p.u.V 1.3 (FoW) 1.1 (CW) 1.0 BIL 0.83 SIL Time Impulse wave shapes <1.2μs 1.2μs 3 - 5μs 50μs
BILFW CW SIL 21 Lightning impulse Full wave 22
LI test connections 25 LI test connections 26
Lightning impulse test sequence Without non linear resistors in the unit
- Reduced (50%) full wave
- 100% Chopped wave
- 100% Chopped wave
- 100% Full wave 27 With non linear resistors in the unit
- 50% Full wave
- 80% Full wave
- 100% Full wave
- 100% Chopped wave
- 100% Chopped wave
- 100% Full wave
- 80% Full wave
- 50% Full wave Lightning impulse test sequence 28
Dielectric tests-Switching impulse
- Sequence Reduced Full wave followed by 2 Full waves (opposite polarity application required to demagnetize core) 31 Switching impulse waveshape 32
Switching impulse connection Reduced FW and FW voltage wave shapes are compared for pass criteria 1.5PU Ph-Ph 33 Dielectric tests-Applied voltage 34
Dielectric tests-Induced voltage 37 Induced voltage test 38
Test voltage and duration
- For class II transformers (>69kV Class)
- Test voltage is raised slowly to 150% and held for few minutes and is raised to Enhancement level of approximately 173% for 7200 cycles and then reduced to 150% and maintained for 1 hour
- During this test partial discharge (apparent charge) in pico- coulombs is recorded every 5 minutes
- As per ANSI-IEEE standards the limit for PD level is 500pC (Alternate measurement can be RIV in micro-volts in which case the limit is 100micro-volts. But this is not a preferred method, was moved to annex in the IEEE standard) Induced voltage test 39 Measurement of partial discharge 40
