Expert Analysis of Lightning Impulse Failure Modes in Oil-Filled Power Transformers Based on Experiential Data

Lightning impulse testing is performed as part of the factory acceptance routine tests in power transformers to check the integrity of the insulation and to ensure that transformer insulation performs according to the design specifications. Lightning impulse testing is a high voltage test and the pass criterion depends on a variety of parameters being met, mainly based on the lightning impulse waveforms. In the event of a test incident, the resultant waveform can be used to classify the fault and through experiential expertise, the waveform can also be used to estimate the location of the fault within the transformer. In this paper, real-life lightning impulse waveforms resulting from a test incident are presented and used to classify the failure as well as the location of the fault.