Partial discharge patterns in conducting and non-conducting electrical trees

S J Dodd,N M Chalashkanov,J C Fothergill

doi:10.1109/icsd.2010.5568217

Abstract

Previous observations on electrical tree growth in epoxy resins has shown that different types of tree growth structure, electrically conducting and non-conducting, can occur dependent on the state, glassy or flexible, of the epoxy resin. In this current study, the partial discharge characteristics were characterized experimentally at a temperature of 20°C within two different epoxy resins systems having glass transition temperatures of 0°C and 50°C. The partial discharge activity (determined from apparent charge measurements) was characterized in terms of φ~q~n patterns using statistical tools. The aim was to compare the apparent charge measurements obtained from conducting and non-conducting electrical tree structures with computer simulations of the partial discharge activity in both conducting and non-conducting electrical trees. The results show that there is a significant relationship between the local extent of the partial discharge phenomena, as determined by the conductivity of the tree channels, and the apparent charge, as shown by the experimental and simulated partial discharge patterns. The implications of this work for partial discharge detection as well as for condition monitoring in real insulating systems are discussed.

Highlights

Electrical treeing is of interest as one of the causes of insulation failure in HV cable insulation, electrical machines, switchgear and transformer bushings
In order to create reliable monitoring system based on partial discharges (PD) pattern recognition it is necessary to improve our understanding on the physical processes governing the PD activity and the way PD patterns evolve with material degradation
The model was not investigated further to determine whether such deterministic models can reproduce the statistical characteristics of the PD patterns observed in the experiments

Summary

INTRODUCTION

Electrical treeing is of interest as one of the causes of insulation failure in HV cable insulation, electrical machines, switchgear and transformer bushings. Experimental observations of electrical treeing under 50 Hz alternating applied electric fields in epoxy and polyethylene insulation materials have demonstrated that that two types of tree could be formed; electrically non-conducting, in which the partial discharges occur within the main branches of the tree structure, or, electrically conducting, in which the partial discharge occur only at the growing tree tips. The current study aims to characterize the partial discharges occurring within the different types of tree structures, in a flexible and a glassy epoxy resin, in terms of the ~q~n patterns using statistical tools. In this work we compare the different apparent charge measurements obtained from experiment with simulations of the partial discharge activity in both conducting and non-conducting electrical trees to obtain a better understanding of the relationship between the local extent of the partial discharge phenomena and the recorded partial discharge patterns

PD SIMULATION

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS