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Partial discharges under HVDC conditions

Judd, M., Siew, W. H., Hu, X., Corr, E., Zhu, M., Reid, Alistair, El-Mountassir, O., Cristobal, M., Guissiani, R. and Seltzer-Grant, M. 2015. Partial discharges under HVDC conditions. Presented at: EuroTechCon 2015, Stratford-upon-Avon, UK, 1-3 Dec 2015. Unspecified. pp. 1-19.

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Abstract

This paper describes partial discharge (PD) phenomena in HVDC insulation, including diagnostic methods that are being developed. PD detection and analysis is used to assess the condition of electrical insulation in many types of HV equipment during manufacture, acceptance testing and condition assessment of equipment in the field. In HVAC systems, the phase of the power frequency cycle has a dominant influence on PD activity. Consequently, phase-resolved PD patterns form the cornerstone of many diagnostic techniques for HVAC insulation. However, this approach cannot be used for HVDC systems. The increasing use of HVDC in recent years has led to a growing interest in how PD diagnosis techniques developed for AC systems can be adapted for use with HVDC equipment. Under the influence of an electrostatic (DC) field, the flow of PD current is unipolar, which means that mobile charges in the insulation are subject to forces that cause them to migrate from one conductor to the other, with conductivity of the insulation playing a significant role. This can lead to the accumulation of localised regions of trapped charge. While PD pulses tend to occur much less frequently under HVDC conditions than under comparable HVAC excitation, this trapped charge can cause bursts of discharge activity when the steady-state equilibrium is disturbed, most notably during energising and de-energising. Measurements are presented to illustrate PD behaviour in various test objects subjected to HVAC, HVDC and composite (HVDC plus modulation) voltages. Additional tests on defective 33 kV cables are described, which include DC ramp tests, polarity reversal and soak testing at DC overpotentials. Results results demonstrate how PD activity can be influenced by comparatively minor features of the applied HVDC voltage, such as those associated with ripple from converter switching. Finally, PD data acquisition and analysis techniques are discussed with a view to optimising the application of PD detection under HVDC conditions.

Item Type: Conference or Workshop Item (Paper)
Date Type: Publication
Status: Published
Schools: Engineering
Additional Information: No online link to proceedings. Research Gate entry: https://www.researchgate.net/publication/286456985_Partial_Discharges_under_HVDC_Conditions
Last Modified: 04 Jun 2017 09:23
URI: http://orca.cf.ac.uk/id/eprint/94366

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