Relationship between Development of Electrical Tree and Frequency Components of Electromagnetic Waves Associated with Partial Discharge

Summary

Defects such as voids in a solid insulator can cause partial discharges that lead to accidents or breakdown. Our group has been investigating a diagnosing method that detects electromagnetic waves associated with partial discharges occurring in a solid insulator. In our previous work, our method successfully identified the partial discharge of epoxy-insulated power equipment in the field. The proposed method can determine whether the point of partial discharge occurrence is inside or outside of the solid insulator by detecting electromagnetic waves. In addition, degradation of the solid insulator can be diagnosed from the frequency characteristics of the radiated electromagnetic waves. However, a clear theoretical understanding of the cause of these characteristics has remained elusive. Because electromagnetic waves due to partial discharge are caused by discharge currents, the frequency of electromagnetic waves is affected by the current, which in turn is caused by charge transfer. The rise time of the pulse current is also assumed to depend on the movement velocity of a charge, which in turn depends on the field strength. Furthermore, in the case of a solid insulator, the frequency is assumed to increase at the time of electrical tree progression because the field strength at the tip of the tree is higher. Therefore, tests were performed to investigate the relationship between electrical tree progression and the frequency components of the radiated electromagnetic waves. Consequently, the waveform of the partial discharge current steepened owing to the higher applied voltage. In addition, the frequency of electromagnetic waves increased as degradation progressed.

Additional informations

Authors

Prykhodko, Skinner, Singhvi