Analysis of evaluating methods for transformer chopped impulse tests

Abstract

Power transformers must be tested under high voltage impulse tests with full-length and chopped wave- forms. This paper compares different evaluation methods used for lighting impulse chopped tests, showing the advantages and drawbacks of them. The evaluation technique compares voltage and current wave- forms corresponding to reduced-level and full-level voltages. Any difference between the waveforms may correspond to a failure in the transformer under test. However, with chopped waveforms, impulse genera- tors may have significant differences in the time of chopping, so that low-level and full-level waveforms are different, making difficult to get a conclusion on the test result. Typical evaluating methods and a new recently proposed algorithm are compared using different power transformers and chopping times.