The developing rules of partial discharge in the inter-turn insulation of transformers under constant AC voltage

In order to research the change of partial discharge (PD) in degradation process of the inter-turn insulation of transformer thoroughly and to explore effective characteristic parameters of the partial discharge, and to use them to diagnose severity of inter-turn insulation deterioration. A discharge test platform is established to simulate the partial discharge of inter-turn insulation. Four voltage levels, 42.5kv, 40kv, 37.5kv, 35kv, are selected through the previous exploratory experiments. By using constant AC voltage, the partial discharge is detected by conventional pulse current signals and experiments are done at least five times under each voltage level., The PD frequency, discharge capacity per second, average discharge capacity, maximum discharge capacity, cumulative discharge capacity and pulse phase are obtained. Some characteristic parameters, such as cumulative discharge capacity, discharge capacity per second, and pulse phase, change more obvious and have certain rules, and these characteristic parameters can provide certain theory basis for detection and diagnosis of the actual transformer partial discharge.