Working Principle of Cable Fault Tester

Working principle of power cable fault tester consists of three main parts: power cable fault tester host, cable fault locator and cable path tester. The host of the cable fault tester is used to measure the nature and total length of the cable fault and the approximate position between the cable fault point and the test end. The cable fault locator determines the exact location of the cable fault point based on the approximate location of the cable fault point determined by the host of the cable fault tester. For buried cables with unknown direction, a pathfinder shall be used to determine the underground direction of the cable. The basic method of power cable fault test is to apply high-voltage pulse to the fault power cable to produce breakdown at the cable fault point. When the cable fault breakdown point discharges, it generates electromagnetic wave and sound at the same time.

The working principle of the application of arc reflection method (secondary pulse method) in cable fault location: firstly, a high voltage pulse with a certain voltage level and energy is applied to the faulty cable at the test end of the cable to make the high resistance fault point of the cable break down and burn arc. At the same time, add the low-voltage pulse for measurement at 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. When arcing, the high resistance fault becomes an instantaneous short-circuit fault, and the low-voltage measurement pulse will change obviously in impedance characteristics, so that the waveform of flashover measurement becomes a low-voltage pulse short-circuit waveform, making the waveform discrimination particularly simple and clear. This is what we call the "secondary pulse method". The received low-voltage pulse reflection waveform is equivalent to the waveform of a wire core completely short circuited to ground. Superimpose the low-voltage pulse waveform obtained when releasing the high-voltage pulse and when not releasing the high-voltage pulse. The two waveforms will have a divergence point, which is the reflected waveform point of the fault point. This method combines low-voltage pulse method with high-voltage flashover technology, which makes it easier for testers to judge the location of fault point. Compared with the traditional test methods, the advantage of the secondary pulse method is to simplify the complex waveform in the impulse high-voltage flashover method into the simplest low-voltage pulse short-circuit fault waveform, so the interpretation is very simple and the fault distance can be accurately calibrated.

The triple pulse method adopts the double impact method to prolong the arc burning time and stabilize the arc, which can easily locate the high resistance fault and flashover fault. The triple pulse method has advanced technology, simple operation, clear waveform and fast and accurate positioning. At present, it has become the mainstream positioning method of high resistance fault and flashover fault. The third pulse method is an upgrade of the second pulse method. The method is to first measure the reflected waveform of the low-voltage pulse without breaking through the fault point of the measured cable, then impact the fault point of the cable with the high-voltage pulse to generate an arc, trigger the medium voltage pulse when the arc voltage drops to a certain value to stabilize and prolong the arc time, and then send the low-voltage pulse, Thus, the reflected waveform of the fault point is obtained. After the superposition of the two waveforms, 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 prolong 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 synchronization time of arc burning, and the operation is also more simple.

Working Principle of Cable Fault Tester 1

 

 

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