Interference monitoring during the factory PD tests of ±800kV converter transformer

Partial discharge (PD) level under the specified AC/DC test voltages, which is one key parameter indicating the insulation reliability of ultra-high voltage direct current (UHVDC) converter transformers, do not often be accurately determined due to the impact of the external electromagnetic interference. To solve this problem, a method that uses the ultra-high frequency (UHF) technology to monitor the PD interferences was brought forward in this paper, and was applied to the factory tests of a ± 800kV converter transformer. The results show that the waveform characteristic of the UHF detection signals can be well used for recognizing the interferences caused by communication equipment, as well as the phase distribution characteristics of the UHF detection signals for the floating potential discharge and the point discharge induced by various types of AC / DC test voltages. The results also confirm that the floating discharge spots and the point discharge spots can be quickly and accurately located by analyzing the arriving time difference of RF signals at the different sensors of the UHF antenna array. Based on the monitoring results, the PD interference sources were well treated and then the ± 800kV converter transformer smoothly passed the partial discharge measurements. The research results will be further deployed to the similar work of the UHVDC converter transformers in the converter stations.