Digital acquisition and processing of partial discharges during acceptance test of HV transformers

A six-channel digital recording system has been developed for monitoring partial discharges (PDs) in the HV insulation of power transformers during acceptance tests. The analog PD signals are converted to digital words describing their apparent charge, polarity and the point on the wave (phase) of the test voltage at which the PD pulse appears. The data are recorded during a 1 s acquisition period, processed, displayed and stored during the time (up to 7 s) the system is preparing for the next acquisition. The complete record of PDs acquired during the test is stored on a hard disk, and specialized programs have been developed for post test evaluation of the transformer performance. Different presentation formats allow easy identification of interference signals induced in the test circuit by external sources, correlation of PD patterns recorded on different transformer windings, and evaluation of changes in PD activity during the test