Research Of Hf And Uhf Partial Discharge Joint Detection To Power Cable Joint

As XLPE cable is becoming more and more widely used in urban distribution power network, power system accidents caused by power cable insulation fault are also increasing. Partial discharge detection to power cable can find the early fault in time and guarantee safe operation of power grid. The cable joint has a larger probability of insulation problem than the cable body because it’s more vulnerable. So the research of partial discharge to cable joint is quite urgent to be explored.Firstly, the high frequency method is researched. Based on the introduction of the structure of the cable, the validity of high frequency current transducer detection is analyzed when cable joint has partial discharge. In order to research the relationship of cut-off frequency, sensitivity and sensor parameters, the equivalent circuit and formulas are researched. Then, with the magnetic core properly chosen and the experimental platform well developed, the effective parameters are adjusted and the sensor with good performance is made to achieve the high frequency method.Then, the ultra high frequency method is researched. For the UHF method, the built-in sensor cannot be applied to the cable in operation, so the external sensor is applied. In the process of using the external sensor, the signal intensity has great attenuation in the process of radiation out of cable joint and propagation in the air, due to the effect of the shield of cable joint and signal characteristics. Such improper sensor installation position will lead to large detection error. For three-phase cross-bonded cable, the shield of cable joint is disconnected. In view of this situation, electromagnetic simulation is conducted to verify the feasibility of using external sensor and find the optimal placement where the signal is strongest. The sensor installing in this place can reduce the detection error caused by signal attenuation, and the problems of external UHF sensors are solved.Finally, the problem that a single method is difficult to distinguish between interference signal and real partial discharge signal is researched. As signal coupling methods and interference sources of these two methods are different, the method of joint detection is adopted to solve the problem in this paper. In the joint detection method, the impulse interference is removed by analyzing that whether or not the two detection results of the pulse signal are simultaneous. Before on-site joint detection, in order to test the reasonability of the best installation location of the UHF sensor in joint detection, the UHF sensor is used during the on-site detection. In order to test the practical effect of joint detection, the joint detection on-site is carried out, and it is proved to be able to identify the interference signal and real partial discharge signal by a field case, with the problem of a single method solved.