The effect of DC superimposed AC voltage on partial discharges in dielectric bounded cavities

Experimental Challenges when Measuring Partial Discharges under Combined DC and High Frequency AC Voltage

“…As it have been indicated previously [1], the repetition rate of the larger discharges increase, the overall repetition rate seems less affected. This can be attributed to the time lag and changes in the overvoltage when AC voltage is added.…”

“…The MPD at the coupling capacitor has a lower gain and can detect larger discharges before saturation. In a previous setup [1], the MPDs was connected to the same measuring impedance, but this effectively halved the signal-to-noise ratio, making it difficult to detect the polarity of the small discharges. The present setup allow a better signal-to-noise ratio and preserve the polarity information.…”

“…It is instructive to consider some of the differences of partial discharges under pure AC voltage and pure DC voltage. The following discussion is based on the ABC circuit model for cylindrical cavities in a dielectric material [1].…”

“…The last decade HVDC systems have gained territory in power transmission to offshore wind parks and oil platforms, using IGBT-VSC technology in the HVDC converter stations. As AC to DC conversion will result in a high frequency ripple voltage on the DC voltage, it will also affect the partial discharge activity in HVDC insulation [1]. Good experimental practice is paramount to push the research within this field further, the present paper will focus on the experimental challenges when designing and building a setup to measure partial discharges (PD) under combined HVDC and high frequency AC voltage.…”

Partial discharge behavior under operational and anomalous conditions in HVDC systems

“…Concerning the principles and the mechanisms of PD under DC fields, remarkable investigations have been carried out [8,9], but the operational nature of HVDC systems introduces some challenges: harmonic injection that appears in the form of ripples in the DC side of the converters influences cable insulation [10]. Some recent studies have focused on PD activity under abnormal conditions that could be imposed by the operational conditions of HVDC equipment, through modelling [11,12] and experimental tests [13,14]. Moreover, cable insulation is influenced by the normal polarity reversal operation of Line Commuted Converters (LCC); this might be due to accumulation of space charges under the effect of DC electric fields [15][16][17] that result in locally intensified fields within the cable insulation.…”