Closed-loop system to control discharge level for studying the effect of long-term corona discharge

In order to study the effect of long-term partial discharge on dielectric gases and determine the relation between gas compositions and PD levels, it is necessary to hold discharge magnitudes in a narrow range. This is not easy due to continuous change in the dielectric medium's chemical composition as well as potential erosion of high voltage conductor and insulator surfaces. A closed-loop control system is proposed here that adjusts the output voltage of the test transformer via a motoroperated variac. As a result of the verification tests under ambient, nitrogen, and a C4F7N/CO2 mixture, the average partial discharge magnitude remained constant with an +/- 3% error.