On-site transformer partial discharge diagnosis

In the lab, partial discharge diagnosis has widely replaced the traditional RIV measurements. Additionally, partial discharge acceptance levels are being reduced due to the increasing use of composite material and a growing awareness of partial discharge phenomenon and their consequences. Adequate filtering of the supply voltage for induced voltage testing and the use of sensitive acoustic measurement has greatly improved the detection and location of partial discharge activity in power transformers. An increasing population of service aged substation equipment having reached their projected service life demands on-site repair and, hence, on-site testing to factory standards. Using inverter based three-phase mobile test sets allows on-site application of tests previously limited to a mere test room environment. Besides the unmatched portability of inverter-based sources, especially the less critical generation of reactive power simplifies on-site testing, if compared with motor-generator sets. Additionally, the lack of high short circuit currents limits the damage in case of breakdown. However, adequately removing the switching noise spectrum becomes a demanding task in order to reach the required sensitivity of the partial discharge measurements.