Uhf and Acoustic Partial Discharge Localisation in Power Transformers

The reliability of electrical energy networks depends on the quality and availability of electrical equipment like power transformers. Local failures inside their insulation may lead to catastrophic breakdowns and can cause high outage and penalty costs. Beside the strength and type of a PD, the geometric PD position is of major interest concerning risk evaluation of the flaw. Conventional PD measurements according to IEC 60270 might show certain drawbacks during onsite and online measurements. The current work presents two so called unconventional methods, the electromagnetic PD measurement method, also known as the UHF-Method and acoustic measurements. The UHF-Method with a bandwidth from 300 MHz up to 3 GHz is based on the fact, that PD inside oil filled transformer emit electromagnetic waves measurable with oil valve sensors inside the transformer tank. Acoustic sensors from outside the tank measure in the ultrasonic frequency range the acoustic emissions of PD sources. For PD localization acoustic measurements are beneficially triggered with sensitive measurable PD signals like e.g. UHF signals, as demonstrated in the paper with the help of an onsite measurement on a large power transformer.