Abstract
This paper focuses on the discharge of cross-linked polyethylene (XLPE) insulated DC cables, which has become a concern of power utilities when carrying out a voltage withstand test or an outage maintenance. Based on the electrical tree initiation test of XLPE block samples under grounded DC voltages, the main cause and key factors for damages of DC insulation resulted by grounding discharge were investigated, and the allowable voltage level to start the accelerated discharge operation was estimated. By the laboratory tests of two XLPE cable samples discharged under different conditions, the basic discharge rules were observed, the equivalent circuit was set up, and the equipment parameters were determined. In addition, a method to estimate the discharge time for cable lines with different lengths was proposed. Finally, the on-site measured data of decay voltage and leakage current were presented for a 200 kV DC XLPE cable line which had been discharged steppedly through a resistance grounding device after the DC voltage withstand test, and the experimental results were found to be in good agreement with the theoretical data.
Highlights
Cross-linked polyethylene (XLPE) cables have been increasingly used in DC transmission and distribution power systems, with an ever higher rated voltage level
Since the time duration of the DC voltage will affect the electrical field built up in the cable insulation and the temperature will affect the charge release, they are expected to have some influence on the discharge procedure of the high voltage direct current (HVDC) cables, which needs to be investigated and clarified through the follow-up studies
Compared with the long-term operation under a stable HV DC voltage, an uncontrolled sudden grounding will be fatal to a XLPE DC cable
Summary
Cross-linked polyethylene (XLPE) cables have been increasingly used in DC transmission and distribution power systems, with an ever higher rated voltage level. The objects were 11 and 6.6 kV three-core AC cables used in the power supply system of big ships, and except for the theoretical analysis based on the R–C (resistance-capacitance) equivalent circuit, no measured data were provided.. Lafaia carried out some experimental and theoretical analysis of the cable discharge process based on the tests, calculations, and simulations of 275 kV pressurized-oil-filled (POF) cables Her contributions included the field and laboratory measurements of voltages and currents during the cable discharge, an estimation method for the leakage resistance and discharge time by a simple R–C parallel circuit, and typical values of the leakage resistance, leakage current, and discharge time for 275 kV AC POF cable systems.. The measured voltage and current data of a long-length 200 kV DC XLPE cable during its discharge process after a field DC withstand test were presented, which verified the research conclusions
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