For accurate diagnosis of electrical equipment insulation defects via partial discharge detection and timely warning of dangerous discharge condition

the oil wedge discharge model is used to simulate the defects between winding turns and cakes of a power transformer.The signals of oil wedge discharge in the process from starting point to breakdown are analyzed by using the constant voltage method and the whole real-time combined high frequency（HF）/ultra-high frequency（UHF）current detection system.The influence of voltage level on the development process of oil wedge discharge is studied by changing the applied voltage.The changes of the characteristic parameters of oil wedge discharge under different voltages are summarized

and the method and principle of state division of discharge phase are proposed.The discharge mechanisms of different stages are explained.This research shows that under constant voltage the oil wedge discharge contains two typical stages

i.e.

the smooth development stage and the accelerated deterioration stage

and the transition from the smooth development stage to the accelerated deterioration stage has obvious mutation process.In addition

different oil wedge discharge has the same statistical features in accelerated deterioration stage.This research may facilitate condition monitoring and warning of partial discharge in engineering.