Modulator system component reliability optimization through monitoring microdischarge activity

A new class of research Microdischarge Analysis (referred to as `Partial Discharge' analysis at large microdischarge activity levels) has been developed as part of research at the High Power Electronics Institute. For the first time, detection of aging-inception subpico-coulomb micro discharges is feasible in practical power electronics components and materials. For a research application where measurements would be taken to assess lifetime and aging, the measurement of microdischarges demanded that the test equipment operate at the thermal noise limit, yet it had to be a field-deploy-able, diagnostic instrument offering 100 times greater sensitivity, wider detection bandwidth, and better transient response properties than are present in current industrial machines. Through a detailed analysis of the measurement requirements and by implementing grounding and shielding techniques the noise level was dropped to 0.1 pC, which the work of Bagirov has shown is near the aging initiation level of many insulating materials. This paper will describe the low noise instrument development, coupled with elimination of ground currents which were found to seriously distort the discharge signatures. Also, other techniques that lead to the improved measurement capabilities for insulation specimens will be explored as they relate to the modulator and component design issue.