Pulse Flashover Method for Fault Detection of High Voltage Cables

Cable has a very important application scenario in our daily life. It can be said that we can't live without cable. In order to ensure the normal use of the cable, it is necessary to regularly detect and maintain the cable. In case of cable failure, the fault point shall be found out in time for maintenance. There are many cable fault maintenance methods. Today, I mainly introduce one of the high-voltage cable fault detection methods, pulse flashover method. For high resistance fault, due to the large resistance at the fault point, the reflection coefficient at this point is very small or almost equal to zero. When measured by low-voltage pulse method, the reflected pulse amplitude at the fault point is very small or there is no reflection, so the instrument can not distinguish it. There are two common high voltage flashover measurement methods, namely DC high voltage flashover measurement method (direct flashover method for short) and impulse high voltage flashover method (impulse flashover method for short). 1、 DC high voltage flashover method (referred to as direct flashover method) when the fault resistance is very high and a stable resistance channel has not been formed, the gradually increased DC voltage can be applied to the tested cable. After reaching a certain voltage value, the fault point is preferably broken down to form flashover. The flashover arc is used to form a short-circuit reflection on the added voltage, and the reflected echo is formed by a high resistance source at the input end to form an open circuit reflection. In this way, the voltage will be reflected many times between the input and the fault point until the energy is exhausted. 2、 Impulse high voltage flashover method (impulse flashover method for short) when the fault resistance is reduced and a stable resistance channel is formed, the DC high voltage cannot be added due to the limitation of equipment capacity. At this time, it is necessary to use impulse voltage test. The DC high voltage charges the cable through the ball gap until breakdown, and still generates short-circuit reflection with the flashover arc formed by it. The measuring inductance L shall be added at the cable input end to read the echo. The radio wave is reflected by short circuit at the fault point and l at the input end, and multiple reflections will be formed during this period. Due to the self induction phenomenon of inductance L, it begins to show open circuit reflection due to the current blocking effect of L, and shows short-circuit reflection after a certain time with the increase of current. The whole circuit consists of capacitor C and inductance L, which constitutes a large process of L-C discharge. Therefore, the wave process at the line input is a nearly attenuated cosine curve superimposed with fast pulse multiple reflection wave. 3、 High voltage cable fault detector is generally used. High voltage cable fault is high resistance fault, and high voltage flashover method is used to measure the distance of fault point. This method uses st-330b cable fault locator as experimental equipment. 1. Wiring mode: firstly, complete the wiring of high-voltage flashover as required; Then, connect the sampler with the ranging host with a double clamp test line, and then place the sampler next to the grounding wire of the high-voltage capacitor. 2. Equipment operation (1) start up, select the sampling method as flashover, the pulse width is the default, the cable type is the physical type, and the reading accuracy is the default. (2) Use the high-voltage equipment to discharge the cable, and then click the orange sampling button on the right to start sampling until the waveform is collected. Press the sampling key again to stop sampling. (3) Study the waveform, move the vernier ruler to the starting point and ending point of a waveform, read the waveform, and the distance of the fault point will be automatically measured in the upper left corner.

Pulse Flashover Method for Fault Detection of High Voltage Cables 1

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