This Paper Briefly Introduces the Fault Detection Method of High Voltage Cable
The discovery and fixed-point work of cable faults has always been a big problem in the electrical measurement industry, mainly because most cables are deeply buried underground, the laying distance ranges from a few meters to a few kilometers, and the on-site environment is complex. In addition to the high quality requirements for cable fault test equipment, the comprehensive quality of technicians is also very strict. There are three common types of cable faults: low resistance fault, high resistance short circuit grounding fault and flashover fault. For different types of cable faults, the fault point detection methods are also very different. The following is a brief introduction to the fault detection method of high-voltage cable. There are two kinds of traditional fault detection methods for high voltage cables: bridge method and pulse method. 1ã€ Electric bridge method is a classical method for ranging power cables. This method is relatively simple, but it needs to know the data such as cable length in advance, and it is only suitable for low resistance and short circuit faults. However, in actual operation, faults are often high resistance and flashover faults. Due to the high fault resistance, the bridge current is very small, so it is difficult for general sensitivity instruments to detect. 2ã€ Pulse method 1. Pulse current method this method is safe, reliable and simple. The method is to break down the cable fault point with high voltage, collect and record the current traveling wave signal generated by the fault click through with the instrument, and calculate the fault distance according to the round trip time between the current traveling wave signal at the measuring end and the fault point. In this method, the pulse current is coupled with a transformer, and the waveform is simple and safe. This method also includes direct flash method and impulse flash method. Different from the pulse voltage method, which uses resistance and capacitor voltage dividers for voltage sampling, the pulse current method uses linear current couplers placed parallel to the low-voltage geodesic and has no direct electrical connection with the high-voltage circuit. It is particularly safe and convenient for recording instruments and operators. So people usually use this method. 2. Pulse voltage method this method can be used to measure high resistance and flashover faults. Firstly, the cable fault is broken down under the DC or pulse high voltage signal, and then the distance is measured by recording the time required for the discharge pulse to go back and forth between the measuring point and the fault point. An important advantage of pulse voltage method is that it does not have to burn through high resistance and flashover faults. It directly uses the instantaneous pulse signal generated by fault breakdown. The test speed is fast and the measurement process is simplified. 3. For low resistance and open circuit faults, the pulse echo method uses the low-voltage pulse reflection method to measure cable faults. Compared with the above bridge method, it is simple and direct. It only needs to observe the time difference between the reflection and transmission pulses at the fault point to locate the fault. During the test, a low-voltage pulse is injected into the cable. When the pulse propagates to the fault point, it will be reflected, and the pulse is reflected and sent back to the measuring point. The time difference between the transmitted and reflected pulses is recorded by the instrument, and the distance of the fault point can be calculated only by knowing the pulse propagation speed. This method is simple and intuitive. It does not need to know the original data such as cable length. It can also identify the position of cable joint and branch point according to the reflected waveform.