1. Cable fault test steps
(1) When the cable fault tester measures cable faults, the tester must first determine the nature of the cable fault in addition to mastering the performance and operating methods of the machine, so that appropriate working methods and testing methods can be adopted. First use a megohmmeter or a multimeter to measure the insulation resistance between each phase and phase at one end of the cable, and determine whether it is a low-resistance short circuit or a disconnected open circuit, or a high-resistance flashover fault according to the resistance value.
(2) When the resistance is lower than 100 ohms, it is a low-resistance fault, 0 to tens of ohms is a short-circuit fault, and the resistance is extremely high to infinitely large as an open circuit or disconnection fault. Whether the wire is broken or not, you can also connect the cable terminal to a universal meter to measure the resistance of the two phases that are short-circuited at the beginning to confirm. This type of fault can be directly measured by the low-pulse method.
(3) When the resistance is very high (hundreds of megabytes and gigabytes) and there is instantaneous discharge during high-voltage tests, such failures are generally called flashover failures, which can be determined by the DC high-voltage flash test method.
(4) The resistance value of high-resistance faults is higher than that of low-resistance faults, which can be determined by DC high-voltage flash test when doing high-voltage experiments.
(5) Determine the points after rough testing in a certain way. If necessary, find the cable path and measure the cable length or distance.
2. Low-voltage pulse test method
The low-voltage pulse test method has the characteristics of simple operation, easy identification of the waveform, and high accuracy. For short-circuit, low-resistance, and disconnection faults, this method can be used to test the fault distance directly. Even if there is no such fault, the low-voltage pulse method can be used to measure the cable length or speed before the general high-voltage flashover test. Compared with the flashover test waveform, it will usually facilitate the waveform analysis and achieve the purpose of quickly determining the fault point.
3. Impact high-pressure flash test method (impact flash method)
The test method is to apply an impulse voltage to the cable through the ball gap to make the fault click through and discharge, and generate a reflected voltage (or current). The instrument records the process of this momentary state, and determines the location of the fault point through waveform analysis. It is the main method for measuring high resistance and flashover faults. The same sampling method is also divided into voltage sampling and current sampling. Of course, the subdivision can also be divided into high-end and low-end voltage sampling, inductance and resistance sampling, and start and end sampling. Because the low-end current sampling connection is simple, reliable and safe, and the waveform is easy to identify, the current sampling method is very practical.
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