Partial discharges caused by internal defects of transformer may lead to aging and damage of oil-paper insulation

or even threaten operation and security of the transformer.In order to explore a method for assessing the severity of transformer defects based on partial discharge signals

three typical defect models of sphere-plate

columnplate and needle-plate were set up in this study

and the characteristic parameters such as partial discharge phase spectrum

discharge number and discharge quantity were obtained.It turned out that the discharge number of the sphere-plate and column-plate models and the average discharge quantity of needle-plate model varied upward then downward

and these inflection points could be taken as the criterion at later stage of the discharge.Furthermore

discharge energy was used to quantify the discharge intensity

and the influences of defect type and discharge stage on the discharge energy were analyzed.On this basis

the discharge severity was divided into three levels-initiation

development and danger.The research results in this paper may be a reference for evaluating partial discharge severity for different defect types.