Cable Fault Tester Working Principle

The power cable fault tester consists of three main parts: the power cable fault tester host, the cable fault locator, and the cable path meter. The cable fault tester host is used to measure the nature of the cable fault, the total length, and the approximate location of the cable fault point from the test end. The cable fault locator determines the precise location of the cable fault point based on the approximate location of the cable fault point determined by the cable fault tester host. For buried cables with unknown directions, a path meter is required to determine the underground direction of the cable. The basic method for testing power cable faults is to apply high-voltage pulses to the faulty power cable to cause a breakdown at the cable fault point. The cable fault breakdown point discharges and generates electromagnetic waves and sounds at the same time.

The working principle of the arc reflection method (secondary pulse method) in the cable fault location is: first, a high-voltage pulse of a certain voltage level and a certain energy is applied to the faulty cable at the test end of the cable to cause the high-resistance fault point of the cable to break down and arc. At the same time, a low-voltage pulse for measurement is added to the test end. When the measurement pulse reaches the high-resistance fault point of the cable, it encounters an arc and reflects on the surface of the arc. Because the high-resistance fault becomes an instantaneous short-circuit fault during arcing, the low-voltage measurement pulse will undergo a significant impedance characteristic change, so that the waveform of the flashover measurement becomes a low-voltage pulse short-circuit waveform, making the waveform identification particularly simple and clear. This is what we call the "secondary pulse method". The received low-voltage pulse reflection waveform is equivalent to a waveform of a wire core completely short-circuited to the ground. The low-voltage pulse waveforms obtained when the high-voltage pulse is released and when the high-voltage pulse is not released are superimposed, and the two waveforms will have a divergence point, which is the reflection waveform point of the fault point. This method combines the low-voltage pulse method with the high-voltage flashover technology, making it easier for testers to determine the location of the fault point. Compared with traditional testing methods, the advantage of the secondary pulse method is that it simplifies the complex waveform in the impact high-voltage flashover method into the simplest low-voltage pulse short-circuit fault waveform, so the interpretation is extremely simple and the fault distance can be accurately calibrated.

The triple pulse method uses a double impact method to extend the arc burning time and stabilize the arc, which can easily locate high resistance faults and flashover faults. The triple pulse method is advanced in technology, simple in operation, with clear waveforms, fast and accurate positioning, and has become the mainstream positioning method for high resistance faults and flashover faults. The triple pulse method is an upgrade of the secondary pulse method. The method is to first measure the reflected waveform of the low-voltage pulse without breaking down the fault point of the cable under test, and then use a high-voltage pulse to break down the fault point of the cable to generate an arc. When the arc voltage drops to a certain value, the medium-voltage pulse is triggered to stabilize and extend the arc time, and then a low-voltage pulse is issued to obtain the reflected waveform of the fault point. After the two waveforms are superimposed, it can also be found that the divergence point is the corresponding position of the fault point. Because the medium-voltage pulse is used to stabilize and extend the arc time, it is easier to obtain the fault point waveform than the secondary pulse method. Compared with the secondary pulse method, the triple pulse method does not need to select the synchronous duration of arc burning, so it is also easier to operate.