DefinePK

Abstract

In HVDC application the converter transformer plays a major role and its insulation system has to be designed to withstand AC, DC as well as transient over voltage stresses. In this work the effect of transient over voltages on the oil impregnated pressboard which is one of the main insulating materials used in converter transformer. Lightning and switching over voltages are generated using impulse generator circuit and the stress withstanding capabilities of the samples have been investigated. The changes in the shape of the impulse wave during surface degradation have been observed. The degraded zone of the insulation is subjected to ATR-FTIR spectroscopy. From the characteristic peaks of the spectroscopy the byproducts formed in the degraded zone of the insulating material due to the effect of lightning and switching impulses have been studied. The surface tracking patterns and the insulation failure due to surface tracking have also been studied.