Occurrence of partial discharge induced by metal particles in high voltage transformer

There are several reasons of failure of power transformers in a system. One of the reasons of failure is attributed to the presence and movement of metal particles in oil. These induce partial discharge due to high electrical stresses, in the transformer. In order to theoretically determine the probability of occurrence of partial discharges in a high voltage 220/132 kV autotransformer only HV winding area is modeled. A metal particle of a given size and L/R ratio is introduced at the bottom of HV winding between inner surface of winding and pressboard barrier. Under the influence of oil flow the particle moves randomly within a predefined set of solid angles. During its upward movement the trajectory of the particle is calculated. The particles during their upward movement have demonstrated three different attributes, viz. (a) the particle escapes without striking a high voltage disc. (b) It strikes a disc, however the electric stress induced by the particle at the disc does not exceed threshold voltage for PD to occur and (c) The disc struck by particle provides adequate stress for PD to occur. The present paper deals with the occurrence of PD using probabilistic method for different sizes of wire like particle