DC Needle-Plane PD Measurements with Superimposed Harmonics

High voltage direct current (HVDC) transmission systems play a crucial role in addressing the challenges associated with the delivery of renewable energy by enhancing transmission capacity. However, their reliance on converters makes them susceptible to the issues related to current harmonics and voltage distortions. It is worth noting that, as of now, harmonics are not typically regarded as detrimental in HVDC systems. Nevertheless, there is a growing concern about their potential impacts on the occurrence of partial discharges (PDs) in cable systems that can cause the degradation of cable insulation. To provide insights into PD behavior under DC voltage superimposed harmonics, the paper investigates PD measurements on a needle-plane electrode configuration following the IEC-60270 standard and applying the stresses of PD inception voltage (PDIV) and 1.5 times PDIV under different harmonic components. The comparative analysis and discussion of PD patterns under different superimposed voltage harmonics are presented, considering effective Phase Resolved PD (PRPD) patterns, PD repetition rates, and severity factors.