Partial discharge characteristics influenced by different temperatures under pulsating DC voltages

The converter transformer is one of the most critical equipment in high-voltage direct current (HVDC) transmission systems. Valve-side windings withstand complex stresses combined with AC, DC, and pulse voltages. Oil-paper insulation is used within most of HVDC converter transformers. Partial discharge (PD) in oil-paper insulation is a major reason for the development of internal faults in HVDC converter transformer. The current paper presents the development process for the PD of oil-paper insulation under pulsating DC voltage combined with AC and DC voltages at different temperature. In the experiments, the artificial insulation defect models were designed to generate PD signals under pulsating DC voltage detected by a Rogowski coil sensor. The Statistical histograms of φ-q-n based on these PD signals were constructed. The variations in initial discharge voltages and φ-q-n of the PDs with pulsating DC voltages generated from different temperature were analyzed. Experimental results showed that the initial discharge voltages and PD phase-resolved distributions of different temperature were different from one another. The findings of the current study are useful in further research on the mechanism and pattern recognition of PDs in converter transformers.