ABSTRACT
Historically the impulse test was considered as a check of the transformer insulation integrity under the stress resulting from the lightning stroke to the nearby section of the line. Significant variation of Partial Discharges (PD) activity and an increasing level during the second half of the test duration may require a repeated drying under vacuum or disqualify the transformer. To locate the PD source, a set of microphones is attached to the transformer tank, and their acoustic signals are registered on a multichannel recorder. The no-load loss measured at the distorted voltage does not correspond to the respective loss dissipated by the transformer in the high-voltage power transmission system that maintains the sine voltage waveform. The impulse voltage has to be reduced from a megavolt range to a few volts to be measured by digital impulse recorder.
