The influence of windings on UHF electromagnetic wave propagation

Ultra High Frequency (UHF) Partial Discharge (PD) location method is based on the time differences of UHF electromagnetic waves from PD source to different UHF couplers. Measuring arrival time of UHF electromagnetic waves accurately is very crucial to PD location. But the diffraction of UHF passing through windings may result in attenuation and time delay, which may lead to failure to locating PD. In order to indicate the feasibility of UHF location technique for PD sources in transformers, the influence of windings on the propagation of UHF electromagnetic wave is simulated using finite-difference time-domain (FDTD) method. Geometric analysis of UHF diffraction around windings is presented in this paper to calculate the time delay along the shortest propagation path, and an arrival time compensating method is suggested. To confirm the feasibility of the compensating method, experiments are carried out on a 220kV power transformer. It is suggested that arrival time PD inside windings can be compensated accurately.