Influence of HVDC converter operation on partial discharge characteristics

This paper presents an investigation into the influence of different operating conditions of HVDC converters on partial discharge behavior occurring within solid dielectrics. Cables at the DC side undergo different stresses due to transients and harmonics that may result in an intensified level of partial discharge (PD) activity and could affect their insulation integrity. Most DC converter schemes, nowadays, are bidirectional with the valve firing angles at the heart of power conversion and power flow control. Depending on the mode of converter operation and the properties of the interconnected AC systems, varying levels of harmonics, either characteristic or non-characteristic, appear on the DC side. By reproducing down-scaled equivalent DC outputs of conventional converters under controlled laboratory conditions, PD pulses occurring under characteristic HVDC voltages have be measured. PD was produced using a range of insulation samples containing known defects and measured using an HFCT sensor. Characteristics of the acquired PD pulses have been analyzed with the aim of finding a promising condition monitoring tool to identify the influence of the superimposed harmonics on PD activity. The results will aid HVDC network operators in identifying incipient cable faults by contributing to diagnostic knowledge rules for interpretation of PD parameters under known operating conditions.