Transformers are the most critical and costly components in AC power systems. Insulation is the weakest link in transformers, and the design and quality of a transformer's insulation system shall be confirmed by performingdielectric tests according to National or International standards. The impulse test is more critical among the dielectric tests, as it verifies the integrity of the whole insulation system of the transformer. However, concluding the impulse test result is difficult when minor discrepancies exist in the earth's current waveforms. This paper presents two such case studieswith distribution class transformers.
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