Discussion on the localization of partial discharge of medium voltage XLPE cable

- Apr 27, 2018-

For cable manufacturers, it has been a time-consuming and laborious task to locate the partial discharge of medium voltage XLPE cable and find the fault point. Because the current partial discharge detection system is equipped with superscalar positioning equipment. The principle of traveling wave method is used in the positioning. This positioning means, for more than the cable end of about 50 meters long after the discharge point of failure, if the waveform can be collected, and strong signal, the use of the first three to determine the location of the fault, the cable through the complex, at the point of failure to open the peeling carefully find the cutting, two retest confirmation, Can quickly find fault location and identify the cause of the failure.

But the traveling wave method for the fault point near the cable end head, there is a blind spot, through positioning can only determine the location of the fault point in the vicinity of the cable end, but at that end of the head, from the end of the number of meters, through a positioning can not be determined, two or more times to determine the fault location. According to the comparative classic Test experience, located in the vicinity of the cable end of the bureau over the point of failure, for shorter lengths of cable, near the cable near the end (the end of the connection with the high-pressure lead) discharge of the waveform of the second waveform of the peak is higher than the peak of the first waveform. Near the distal end of the cable (the side of which is not connected to the High-voltage lead) the waveform whose second waveform is collected is lower than the peak of the first waveform. Sometimes in order to confirm the accuracy of the test, we need to constantly replace the proximal end, repeated measurement and comparison confirmation. Through two measurements, it can be determined that the cable bureau is located near the end of the cable. To determine the exact location of the fault point, we can use the terminal connection method for three times to locate, the cable good and the fault phase of the conductor and metal shielding in close to the fault point of the connection, immersed in the test insulating oil, the cable end of the discharge to the middle of the cable position, three times to identify the location of the fault, At this time, when the fault location is computed, the length of the cable should be the sum of the fault phase length and the good phase length. If the three-core cable in the body of the connection, the calculation of the length of the cable should double.

Generally through three checks to verify that the cable bureau put over the point of failure of the location can be determined. Once the cable is near the end of partial discharge in the vicinity of the phenomenon, the actual process of locating the fault point is very time-consuming and laborious, and sometimes in order to find the cable fault location, may cause a large number of equipment test time occupied, resulting in the backlog of inspection products. Seriously affected the production progress. Due to the partial discharge location of XLPE cable, there is no effective precise fixed-point method. At the same time, the error is larger after the partial discharge is located near the end of the cable.

As a result, the actual cutting waste and test strength of cable end in actual rewinding process are quite large. One of the situations encountered in multiple localization must be noted: Sometimes the voltage in the cable can be repeatedly positioned, because of the cumulative effect of space charge, the discharge of cable fault position will be weakened and temporarily extinguished. The cable positioning process is not able to capture waveform, resulting in the positioning work can not continue to carry out. In this case, we have to put the cable static for a period of time, waiting for partial discharge over the signal after the reappearance of four or more times positioning.