Impacts of the frequency effects on partial discharge characteristics of the high frequency power transformer insulation

Abstract

The High-frequency power transformer (HFPT) is a new type of intelligent distribution equipment. It is easy to fail under high frequency voltage, the main cause of which is partial discharge (PD). A comprehensive test system is established to study the impacts of the frequency on PD characteristics. The PD inception voltage (PDIV), PD times, and PD mean amplitude of polyimide film are measured under the frequency 1∼50 kHz. The adaptive algorithm is established to decompose and reduce the noise so as to acquire the pure PD signal and achieve the effective characteristics. Also the insulation lifetime is recorded to illustrate the relationship between PD and aging state. Furthermore, the frequency-dependent characteristics of several typical PD parameters are elucidated in details using the method of equivalent microcircuit which can explain the PD activities under high frequency voltage. The experimental results show that with the increase of frequency, PD mean amplitude and times of polyimide film see downward trends after first increase while the PDIV keeps roughly constant with frequency variation. Through the analysis, the frequency-induced space charge accumulation effect plays a dominant role in the above physical changes under high frequency, whereas, the frequency stress changes the insulation permeability as well as the tangential E-field vector, which executes a prominent impact on the PD development under low frequency. It is worth noting that the lifetime is greatly shortened as the frequency increase which is different form the trend of PD characters, showing that there is no direct relationship between PD and the insulation lifetime.