Impulse and subsequent AC partial discharge properties in cast resin transformer

Withstand lightning impulse voltage test is generally carried out for guaranteeing equipment's insulation performance. On the other hand, it is concerned that other insulation performances are influenced by applying impulse voltage. For example, an AC PD (partial discharge) test changes after a number of impulse voltage prestress is applied to a cast resin transformer (CRTr). This paper deals with detection of impulse PD and subsequent ac partial discharge properties in an actual CRTr having artificial defects in manufacturing process. The lightning impulse voltage prestress effect is evaluated by measuring PD inception voltage (PDIV) and PD extinction voltage (PDEV) before and after the prestress.