Study On The Insulation Diagnosis System Of Cable Based On The Polarization/depolarization Current Method

With the development of power industry, cross-linked polyethylene(XLPE) cable is widely used in power transmission and distribution systems. Health status of the cable insulation is related to the reliability of power grid. XLPE cable will be inevitably affected by the factors of process, moisture, heat, electric field, external force in laying and operation, resulting in insulation deterioration. So it is necessary to study the XLPE cable insulation diagnosis technology so as to achieve the early detection of potential failures of cable insulation and the prevention of cable power supply accident. The polarization/depolarization current(PDC) method can diagnose insulation condition by applying DC excitation on the cable, then measuring the current response, and the wide frequency domain of the insulation can be obtained through the transformation from time domain to frequency domain. Compared with the traditional methods, PDC method has the advantages of non-destructive measurement and abundant parameters, and has become one of the focus of the current state of XLPE cable diagnostics.The cable insulation diagnosis methods are introduced and it is decided to develop the cable insulation diagnosis system based on PDC method. According to the field cable condition, the electromagnetic and leakage interference in the field testing of PDC method are analyzed, and the test circuit of anti-interference is proposed. At the same time, the method of measuring the weak polarization and depolarization current in the wide range is proposed. Based on the anti-interference analysis, a set of testing equipment hardware is developed. Meanwhile, a set of human computer interaction software is developed to stably collect the polarization depolarization current of cable. The software can reliably drive the hardware test equipment to carry out the test of polarization and depolarization to cable, and then the test data are analyzed in time domain and frequency domain so as to obtain the insulation state of cable.In order to verify the accuracy of the insulation diagnostic equipment, the current measurement accuracy of the equipment is verified. The PDC method is used for testing the cable with different degree of aging in laboratory. It is found that the equipment can accurately distinguish the aging state of the laboratory cable. At last, the equipment is applied to test the five XLPE cable transmission lines of Zhuhai power supply company, and advices on maintenance for each line are given. The results show that the connection of economic housing distribution wire has serious water intake failure, which has further validated the feasibility of the PDC insulation diagnosis system.