What are the steps and methods for cable fault finding?

At present, there are many methods for finding cable faults. There are also many domestically produced cable fault testers, and the principles are not the same. The common ones are bridge method, pulse oscilloscope method, induction method, and acoustic measurement method. When looking for cable faults, the inspection method should be selected according to the specific site conditions and the nature of the cable fault.

Measure the location of the fault point

After determining the characteristics of the cable fault, it is necessary to select an appropriate method to measure the location of the cable fault point according to different cable fault conditions, that is, fault location. Due to the influence of instrument accuracy and cable laying path, fault location can only be determined by distance measurement, which is called fault location. Commonly used ranging methods include bridge method, low-voltage pulse method, and flashover method.

Among these methods, the low-voltage pulse method is widely used at present. For example, the cable fault tester is measured in this way.

The cable fault tester mainly includes a complete set of tester, pulse generator, rangefinder and fixed point meter.

low pressure pulsed light method

The principle of the low-voltage pulse method to detect cable fault current is that the pulse generator of the instrument sends out a pulse wave, which is sent to the cable fault phase through the lead wire, and the pulse propagates along the cable core to the fault point. Since the wave resistance of the faulty cable is changed due to the reflection of the pulse signal, use an oscilloscope to record the interval between the transmitted pulse and the reflected pulse at the test end, that is, you can calculate the distance to the fault point at the test end

Determination of the nature of cable faults

The detection method of a cable fault depends on the nature of the fault, so the first step in detection is to identify the nature of the fault. Insulation resistance tests are used to determine the nature of cable faults.

1. Ground fault.

2. Short circuit fault. Two or three cores of the cable are short-circuited, or two or three cores are short-circuited to ground.

3. Disconnection problem failure. Generally, 1MΩ is used as the dividing line, and less than 1MΩ is used as a low-blocking line to cause failure. In principle, it can be called a high-resistance line fault by accurately measuring the capacitance of the data cable and judging the system fault point by the capacity of the electrical equipment.

4. Flashover failure. This kind of failure often occurs in the middle joints and terminal heads of cables, and may occur during operation and preventive tests.

5. Hybrid failure. The simultaneous occurrence of two or more of the above faults is called a mixed fault.

HZ-501B Cable Fault Location System