Abstract
Electrical treeing (ET) can irreversibly deteriorate the insulation of polymeric power cables leading to a complete failure. This paper presents the results of an experimental investigation into the effects of unipolar and polarity reversing DC voltages on electrical tree (ET) and partial discharge (PD) behavior within high voltage direct current (HVDC) cross linked polyethylene (XLPE) cable insulation. A double needle configuration was adopted to produce non-uniform electric fields within the insulation samples, potentially leading to electrical trees. The development of trees was monitored through an optical method and the associated partial discharge signals were measured through an electrical detection technique, simultaneously. The analysis of the results shows reasonable relation between the formation of ETs and the type of the applied voltages. The polarity reversing attribute of the test voltages has a pronounced effect on formation and growth of electrical trees. This implicates an interaction between the space charges that accumulate within polymeric materials and the operational polarity reversing electric fields, which causes insulation degradation. Therefore, study of influencing HVDC operational parameters on insulation degradations can contribute to improvements in cable design and advancement in insulation diagnostic strategies applicable in HVDC systems leading to more effective asset management.
Highlights
HIGH voltage DC interconnections can overcome technical, economical, and operational challenges in power networks
The camera was attached to the microscope through phototubeasand connected operation of an high voltage direct current (HVDC) link in either polarity; DC voltages of linearly increasing function were to a desktop computer to record images of the process of prospective treeing within the samples for applied to the test sample, in a way the voltage increased from zero level with the rising rate of 500 further analysis
The first scenario can be considered as the long-time operation of an HVDC link in either polarity; DC voltages of linearly increasing function were applied to the test sample, in a way the voltage increased from zero level with the rising rate of 500 V/s to a predetermined value
Summary
HIGH voltage DC interconnections can overcome technical, economical, and operational challenges in power networks. Since significant progress has been made in design and manufacturing technologies of power cables, electronic valves, converters, and linking configurations, which facilitate higher voltage HVDC connections and interlinks worldwide. Polymeric cables are employed in HVDC systems operating based on voltage source converter (VSC) technology, where the interconnecting power cables are not expected to experience operational voltage polarity change for the purpose of power flow redirection. Incentives towards employment of more environmentally friendly insulating materials and the technological advancements are among the drives to adopt polymeric power cables in HVDC systems which are based on line commutated converter (LCC) schemes [3]. Polymeric cables are primarily influenced by the phenomenon of space charge accumulation. The space charges are Energies 2018, 11, 2406; doi:10.3390/en11092406 www.mdpi.com/journal/energies
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