Partial Discharge Measurement and Evaluation Techniques for-Transformers

For an efficient power transmission and distribution it is imperative that the used high voltage equipment operate at their maximum load without sustaining any malfunctions. Especially transformers, which are needed at the junctions of energy supply systems, have an exposed importance due to the widespread negative consequences resulting out of a failures: For power levels up to 24 MVA with a maximum voltage up to 36 kV beside paper-oil insulated -transformers so called dry type transformers usually insulated by epoxy-resin are used. These transformers are especially sensitive to Partial Discharges (PO) often resulting in irreversible degradation and destruction of the insulation, 'thus finally a breakdown of the whole system is unavoidable. therefore in this contribution some aspects of PD measurements on dry type, transformers are presented with a special focus on the problems arising under noisy conditions, which are typical for measurements on-site. It is described how the quality of an online measurement can be improved using different techniques for measuring and evaluating partial discharges. Furthermore a new PD monitoring system is introduced enabling not only the detection of the discharges but also the localization of the. PD-origin. This system is efficient and cost-effective and can be easily installed at almost all categories of dry type transformers. For paper-oil insulated transformers other PD-evaluation methods are,prefeilable due ts the distinctions of the insulation type and the higher voltage levels used. Different techniques for-measuring partial discharges are compared and a new method is introduced, which enables beside the determination of the apparent charge a localization of the PD-sources by using. The transfer functions of the transformer coils. The advantages and dis advantages of this, new technique compared to conventional methods are discussed leading to an out-look. on future trends in PD-analysis on power transformers in operation.