The method of power cable fault location and high resistance cable fault location

Author: Noyafa–CCTV Monitor Tester

Power cable fault location and high-resistance cable fault location method Power cable fault and high-resistance cable fault are both common problems of cable faults, and they are also medium and high-frequency problems of cable faults. Point location and high-resistance cable fault location method Power cable fault and high-resistance cable fault are both common problems of cable faults, and also belong to the medium and high frequency of cable faults. Everyone has a certain reference when encountering cable faults. Power cable fault location method: In view of the problem that it is more difficult to determine the location of the fault point after the failure of the buried power cable than the overhead line, a representative example of the location process of the fault point when a high-resistance fault occurs in the 10 kV cable is selected. According to the nature of the fault, the method of using the secondary pulse method to locate and locate the fault point is introduced. For high-resistance faults that occur during the operation of the cable, first check the relevant information of the cable to master the detailed information of the cable; use a multimeter and an insulation resistance meter to determine the type of cable fault, and determine the corresponding test method according to the type of fault; use a fault tester to test the cable's fault. Length, check whether the test results are consistent with the data, and preliminarily determine the distance of the fault point; finally, the secondary pulse method is used to accurately locate the fault point to find the fault point, strip the cable to find out the cause of the cable fault, so as to take corresponding preventive measures.

This method is easy to master, especially for short-distance faults, the test waveform is easier to analyze, the fault distance can be quickly determined, and the cable testing efficiency is higher, and the fixed-point positioning time is shorter. Power cable faults are complex and diverse, and can be divided into open faults and closed faults according to the surface phenomenon of the fault; according to the grounding phenomenon, they can be divided into ground faults, interphase faults, and mixed faults; according to the fault location, they can be divided into joint faults and cable body faults; according to the nature of resistance It is broken line fault, mixed line fault and mixed fault, among which, mixed line fault is divided into low resistance fault, high resistance fault and flashover fault. 1. Fault detection methods For different cable faults, the usual detection methods include low-voltage pulse method, pulse current method, secondary pulse method, bridge method, pulse voltage method, etc. [3], this article only introduces three commonly used detection methods .

2. Low-voltage pulse method The low-voltage pulse method is suitable for detecting low-resistance faults (fault resistance is less than 200ΩIt can also be used to measure the length of the cable, the propagation speed of electromagnetic waves in the cable, and distinguish the intermediate head, T-joint and terminal head of the cable. 3. Pulse current method The pulse current method generally includes the impulse flash method and the direct flash method. The linear current coupler is used to collect the current traveling wave signal in the cable, and the fault test waveform diagram is generated, so as to realize the fault condition and measure the fault point distance through the waveform. Purpose. The direct-flash method is used to detect flashover breakdown faults, that is, the resistance at the fault point is extremely high, and when the voltage is raised to a certain value with high-voltage test equipment, a flashover breakdown fault will occur.

The rush-flash method is also suitable for testing most of the flashover faults. Since the waveform of the direct-flash method is relatively simple and it is easy to obtain more accurate results, the direct-flash method should be used as much as possible. 4. Secondary pulse method With the cooperation of high voltage signal generator and secondary pulse signal coupler, secondary pulse method can be used to measure the fault distance of high resistance and flashover faults. The waveform measured by this method is simpler and easy to identify. Locating methods for high-resistance damage in power cables In order to preliminarily determine high-resistance damage in power cables, a combination of high-voltage reflection methods is usually used: pulse arc method and vibration discharge method.

In this article, we will consider the main ideas embedded in these methods and how they work. Additionally, we will discuss devices that implement both approaches. First, the pulse arc method (ARM) is used to determine the high resistance damage The main idea of ​​the pulse arc method is to use a special high-voltage pulse generator. For example, in the arc cable generator of the power cable, the oil first created the conditions for the generation of high resistance defects, Causes short-term arcing (breakdown) to occur.

Depending on the magnitude of the leakage current and the power of the current source, use one of two ways in which the generator acts on the cable: 1. Smoothly charge the KL's own capacity (cable) from the generator current source until breakdown occurs. This method can be used if the leakage is so small that the power supply of the high voltage pulse generator is sufficient to charge it before breakdown. For serious leaking defects, this method does not apply.

2. Charge the capacitor built in the generator to the required voltage (not exceeding the test standard), then run the cable“Instantaneous”Discharge, in this case a high-voltage pulse propagating in the cable wire, which reaches the location of the defect can cause a failure. This method can be used to search for defects on cables with severe leaks. In both cases, the use of an inductor integrated in the generator delays the arc burn time.

A current pulse from the breakdown (propagating from the defect to the input of the generator) triggers a synchronous circuit that initiates a low-voltage sounding through a cable fault locator (also known as a cable fault tester). The physical properties of the arc have low resistance and the probe pulses of the cable fault locator are also reflected from it as well as from low impedance defects (short circuits). Advantages of the pulsed arc method The pulsed arc method (ARM) for determining high resistance damage has several advantages.

This is a non-destructive method because, unlike burning, the effect of high voltage on the cable is short-lived, unlike burning, this method does not reduce cable parameters as a whole, and where insulation resistance is still within normal limits cause new damage. ARM is actually a high precision method because the measurement is actually done by the pulse method. 2. Vibration discharge method (ICE/Dampening) for high resistance damage Vibration discharge method is used to find damage on very long cable lines, or when the damping of the pulse of the underground cable fault locator is too large for some reason and cannot be applied In the case of the pulsed arc method.

The vibratory discharge method allows you to locate most of the faults that can be detected using the pulsed arc method, but usually reduces accuracy. It should be noted here that the function of the cable is not shown when operating by the vibration discharge method. Method of current oscillating discharge (current fluctuation method, ICE) When using the wave current method, the oscillating circuit is formed by the system: capacitor on the source side - cable wire - low transition resistance (or arc) at the defect site.

When using the method of vibration discharge by current, depending on the leakage current value and the power of the current source, here as with the pulse arc method, one of two methods of exposing the cable to the generator is used: 1. From the generator current The source charges the CL capacitor smoothly until breakdown occurs. This method can be used if the leakage is so small that the power of the current source is sufficient to charge it before breakdown. For serious leaking defects, this method does not apply.

2. Charge the capacitor built in the generator to the required voltage (not exceeding the test standard), then run the cable“Instantaneous”discharge, in which case a high voltage pulse propagates in , reaching the defect site and causing breakdown or a large discharge current. This method can be used in searches for leaking serious flaws. A pulse of discharge current returning to the source will charge its capacitor, which in turn.

The wave that reaches the defect may cause a discharge in it again (in which case its polarity changes), or if a second discharge does not occur, it will be reflected with the same polarity, repeating the process again until until all the energy of the initial pulse is gone. These vibrations are displayed on the screen of a cable fault locator connected to the cable via an inductive sensor. Advantages of the Vibration Discharge Method This is a non-destructive method because, unlike combustion, the effect of high voltage on the cable is short-lived. Unlike combustion, this method does not reduce the cable parameters as a whole, and the insulation resistance is still in the normal range. No new damage will be done in place.

This method does not require an explosive arc to be ignited at the defect, so it can help if the arc does not ignite for some reason. For example, a clogged cable may have lower resistance at the defect, but not arc. The cable fault test method introduced in this paper has general reference value.

The cable high resistance fault is a type of fault that is difficult to detect at present. When a fault occurs, the main steps to determine the type of fault and locate the fault point are as follows: (1) Check the cable related materials to master the details of the cable; (2) Determine the type of cable fault, Determine the corresponding test method according to the fault type; (3) Test the length of the cable and check whether the test results are consistent with the data; (4) Preliminarily determine the fault point; (5) Use the secondary pulse method to accurately locate the fault point; (6) Strip the cable to see the actual cable failure and find out the cause so that you can take appropriate preventive measures. With the rapid expansion of the application range of power cables, how to effectively improve the accuracy and rapidity of power cable fault detection and improve equipment management level is a skill that professional technicians must master. For cable high-resistance faults, the secondary pulse method is used for distance measurement, and the test method is easy to master. Especially for short-distance fault test waveforms, the distance measurement method is simple, the degree of automation is high, and it is easy to determine the fault point, which makes the cable detection more efficient and takes less time to locate. Shorter.

The detection method is convenient and effective, and can be used for reference in the handling of similar faults. Shenzhen Noyafa Electronic Technology Co., Ltd.