OWTS Used For Short Cables Fault Detection And Location

The Oscillating Wave Test System(OWTS), which is an advanced PD diagnostics technology of power cables, is suitable for on-site cable insulation fault detection and location off-line.Since 2008, the first OWTS for lOkV power cables had been introduced from Germany by Beijing Electric Power Company,which made a Satisfactory test results and effectively excluded a number of potential insulation fault of 10kV power cables that had put into operation and improved the level of state maintenance of distribution network in Beijing.In view of the advancement and effectiveness of OWTS,it is necessary to carry out a comprehensive study of the technology.The short cable that is in large number in Beijing is special in electrical parameters compared to long cables.Based on the principle of OWTS,the equivalent capacity and the length of short cables is much smaller than the normal one,bringing negative impact to the detection.The smaller capacity leads to high frequency of damped oscillation voltage that differs from the situation of power frequency,which decreases the credibility of PD test.In addition,the smaller length results in the mixture of the incident-reflected pulses in time domain because the PD pulse spreads faster in short cables,which can cause failure location.This paper discusses those problems mentioned above and proposes solution to the problems. Connecting Compensation capacitor in parallel makes the frequency of damped oscillation voltage to a reasonable range that is closed to power frequency by increasing the equivalent capacity of cables.The optimization of detect unit and amplifier is able to enhance the ability to distinguish the incident and reflected pulses in time domain and shorten the time difference in failure location, improving the insulation fault location for short cables. This paper proves the feasibility of the proposal by simulation and the effectiveness of OWTS to detect and locationthe insulation fault for short cables through diagnostics on laboratory and on-site.