The LCC-HVDC ultra-high voltage direct current transmission technology

with its good economic and technological advantages

has become a supply mode for large-scale transmission and large-scale consumption of new energy. However

its harmonic voltage problem is prominent

seriously threatening the electrical performance of the oil paper insulation of the converter transformer. However

there are few reports on the partial discharge characteristics and breakdown failure laws of oil-paper insulation that take into account the influence of harmonic voltage. This article experimentally analyzes the partial discharge characteristic parameters and the WeiBull failure law of breakdown voltage of oil-paper insulation system under typical electrode structures (needle-plate

ball-ball) under different frequencies and contents of harmonic voltage superimposed at power frequency. Based on this

the influence mechanism of harmonic voltage on the starting voltage

PRPD spectrum

apparent discharge quantity

and discharge pulse number of oil-paper insulation partial discharge is analyzed in depth according to the variation law of composite voltage excitation waveform. The results show that the 5th and 13th harmonic voltages reduce the partial discharge inception voltage in oil-paper insulation

exhibiting a “peak weakening effect”

while the 7th and 11th harmonic voltages exhibit a “valley enhancement effect”.When the harmonic voltage content and the amplitude of the applied power frequency voltage reach a certain threshold

the PRPD spectrum of oil-paper insulation partial discharge forms a phase “peak” phenomenon within half a cycle

and multiple discharge phases are symmetrically distributed along the 90°and 270°axis. Harmonic voltage can cause a decrease in the breakdown voltage of oil-paper insulation

and the 5th and 13th harmonic voltages have a greater impact on the breakdown strength of oil-paper insulation compared to the 7th and 11th harmonic voltages. The results of this article will provide reference for the analysis of the electrical aging life of oil-paper insulation in converter transformers and the high reliability design of insulation structures.