Development Of An On-line Partial Discharge Detection System For Power Cables

Power cable is an important part of the power system, whose reliableoperation is very important for the whole power system. Although XLPE powercable has good insulating property, the running and latent failures ofen occurdue to the complex operating environment, the defects producted during thelaying installation and other reasons,.Partial discharge test is one of the best method for assessing the insulatingcondition of XLPE cable, and it is helpful to found the early hidden faults andprevent insulation breakdown accident occurred by monitoring PD. Thetechnology of on-line partial discharge detection for power cables is currently aresearch focus at domestic and abroad, but it has not been universal application,the key problems are the method of extracting partial discharge signal and how tosuppress field interference.In order to realize on-line partial discharge detection for the after-layingpower cable and suppress interference occurring in the on-site measurement,, thecombination method with HF and UHF measurement is put forward afteranalyzing the researching status at domestic and abroad. The HF current sensorand UHF sensor is developed based on the principle of Rogowski coil andArchimedes spiral antenna, respeactively. The impedance matching circuit, signalconditioning circuit, and the partial discharge data acquisition system based onVC++are designed. At the same time, a new partial discharge interferencesuppression strategy is proposed through the property analysis of the fieldinterference signals and partial discharge signals. An on-line partial dischargedetection system for power cables is established at last.The test results for the developed sensor and signal conditioning circuitshow that the sensor has the good detection sensitivity and frequencycharacteristic, and the signal conditioning circuit can complete the processing ofamplification, filtering, envelope detection, which can satisfy the requirements of partial discharge on-line detection for XLPE cable. And the processing resultsfor measured data on-site show that the proposed suppression strategies cansuppress the interference well.In order to validate the availability of the on-line partial dischargedetection system, the experiments were carried out on the power cable withdefects in body insulation and end insulation in laboratory, The measured resultsshow that the system can effectively detect the HF and UHF signals of partialdischarge with the sensitivity lower than10pC, and there is a goodcorresponding relation between HF signal and UHF signal in time domain, whichmakes open time window method can be used to remove random pulse-typeinterference during the on-site measurement.The field test result also shows thatthe system has a good detection effect.