What Are the Methods of Cable Fault Detection

The fault types of power cable mainly include parallel fault and series fault. Series fault refers to the disconnection of multiple or one conductor in the cable. Usually, it is difficult to detect the series fault before disconnecting a conductor in series. It is easy to find the series fault only when there is a real short circuit. Parallel fault is caused by external insulation aging caused by cable overload operation for a long time, and then partial discharge, resulting in parallel fault. The cable fault different from the length difference and resistance value is broken down, and the cable fault can be divided into high resistance type, low resistance type and open circuit fault. So what are the methods of cable fault detection? Bridge method: bridge method is a traditional method of cable fault detection, which can achieve very ideal results. This method is convenient and fast with high detection accuracy. It belongs to a common cable fault detection method. However, due to the low bridge voltage difference and galvanometer sensitivity, it is only suitable for fault detection with small cable resistance. Moreover, it is difficult to detect the open circuit fault of equipment and cable with high resistance. High voltage bridge method: high voltage bridge method is a common fault detection method in cable fault detection. Its detection principle is that in the high-voltage bridge, when the constant current power supply pierces the cable, it will ensure a large bridge current to a certain extent, so as to form a certain potential difference on both sides of the overall bridge, so as to count the fault points on the basis of coordinating the bridge. This method is suitable for high voltage constant current power supply, and can effectively expand the detection range of high resistance of bridge. Relatively speaking, the result is more convenient and accurate. In addition, for the research theory of bridge method, the characteristics of cable centerline resistance and proportional distribution of the whole line can promote the formation of bridge detection system. Impulse high voltage flashover method: impulse high voltage flashover method is widely used in some methods of cable fault detection. The detection principle of this method is to apply impulse high voltage at the beginning of the faulty cable, so that it can quickly puncture the place where the fault occurs, and record the data information of voltage sudden change at the moment of the fault place. Through the analysis of wired fault point and wired initial data information, the time distance is tested, so as to obtain the fault location and uncertain countermeasures. Low voltage pulse reflection method: when low voltage pulse emission method is used to detect cable fault, low voltage pulse shall be injected into the damaged line. When the pulse is transmitted along the cable to the fault point, when the inappropriate impedance is encountered in the process of transmitting current, the reflected pulse is displayed on the detection device and reflected through the data record of the device, and then the round-trip time difference of the output pulse and the cable wave speed are calculated, so as to obtain the distance between the fault point and the test point. This method is very simple and can make the test results particularly significant. When it is difficult to determine the fault data, it can be detected directly. However, it also has disadvantages, that is, it is not suitable for high resistance fault and flashover fault. Secondary pulse method: for the secondary pulse method, it is effectively applied to form the impulse high-voltage pulse at the moment of the integrated high-voltage generator and introduce it to the cable fault location. On the premise of effectively piercing the fault location, it can prolong the uninterrupted time of arc formation at the fault location after breakdown. Obviously, it must be clear that at the same time, a trigger pulse can trigger the automatic trigger device of the secondary pulse and the operation of the cable detection instrument. On the basis of starting the automatic trigger device of the secondary pulse, two low-voltage pulses are transmitted. Through the device of forming the secondary pulse, the cable is effectively transmitted on the fault detection cable, so as to break down the cable. Using the cable fault detector, observe the floating characteristics of voltage waveform and the reflection wavelength in the whole process of forming arc, comprehensively and systematically record the screen of detection equipment, and distinguish various current fluctuations, one of which reflects the actual length of cable and the other reflects the actual distance of short-circuit fault.

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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. 1、 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. 2、 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.
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