Influence of harmonic voltage on characteristics of partial discharge in oil-paper insulation at HVDC converter transformer

Summary

With the increasingly widespread application of high voltage direct current (HVDC) system, partial discharge (PD) of insulation materials under distorted voltage has become a focus of recent research. Voltage distortion is most severe on the valve-side of windings in converter transformers, and it is caused by harmonic voltage generated via the converter. Therefore, it is necessary to study influence of harmonic voltage on partial discharge behaviour of oil immersed insulation. Partial discharge tests were performed on oil-paper insulation with needle-plane electrode system under harmonic and DC superimposed voltage. Before tests, simulation of 12-pulses converter has been done and magnitude of different harmonics has been obtained. Test voltage is applied in accordance with the simulation results. Feature parameters of PD are acquired by pulse current method system. In PD tests, both single harmonic voltage and multiple harmonic voltages have been applied to electrode, and influences of harmonic numbers PD were also studied. Test result shows that the inception voltage of PD has large relation to do with the harmonic numbers, while the distribution of PD pulses is similar to PD under AC voltage. Discharge magnitude becomes larger when the harmonic numbers increased, and the highest discharge magnitude is likely to appear at the peak value of voltage change rate. Phase of different harmonic voltages will change both distribution and magnitude of PD pulses, and pulses distribute at phase with a large voltage change rate. It reveals that characteristics of PD are severely influenced by harmonic voltage and the discharge magnitude becomes higher when number of harmonic voltages increased. Results should be of interest to HVDC operators and will contribute to the development of equipment online diagnosis in HVDC system.

Additional informations

Authors

Gurevich, FRECHEN, STUNDER, ASTO SOTO, Lee, Litinsky Alexander

Keywords

HVDC, Harmonic voltage, Partial discharge, Oil-paper insulation