NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
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NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Author: Noyafa–CCTV Tester
The precise location of cable faults is the key to fault detection. ① ． Acoustic measurement method This method is to find out the fault point by listening to the discharge sound of the fault point when applying a high voltage pulse to the faulty cable to make the fault puncture and discharge. The method is easy to understand, but often the precise location of the cable fault is the key to fault detection.
①. Acoustic measurement method is to find out the fault point by listening to the discharge sound of the fault point when a high-voltage pulse is applied to the faulty cable to make the fault tap through and discharge. This method is easy to understand, but it is often difficult to distinguish the sound of the real fault point discharge due to the relatively large ambient noise or even when the cable is buried too deep, and the sensitivity of the ear is limited, resulting in low test accuracy (generally, the test error is greater than 1 meter). ②. Acoustic-magnetic synchronous detection method This method also needs to apply high-voltage pulses to the faulty cable to make the fault puncture and discharge.
When a high-voltage pulse signal is applied to the cable, a pulsed magnetic field signal will be generated around the cable, and at the same time, a discharge sound signal will be generated due to the discharge of the fault point. Because the magnetic field signal propagates very fast (approximately the speed of light, 30 10,000 km/s), sound signals travel at a slower speed (about 340 m/s), and there will be a time difference when they reach the ground. The magnetic field and sound signal are received on the ground by the probe of the instrument, and the time difference is calculated. Move the probe over the cable to find the place with the smallest time difference, just below that is the point of failure.
Using this method improves the ability of anti-noise interference, but also improves the accuracy of the fixed point (error less than 0.1 meters), the signal is easy to understand and distinguish. ③. The audio signal induction method is mainly used by the path meter to find the direction of the cable path. It is also possible to locate short-circuit faults with fault resistance less than tens of ohms and disconnection faults with a short distance: add the audio signal between the faulty phases, and the signal received by the path meter receiver just above the fault point will suddenly increase. After passing the fault point, the signal will obviously weaken or disappear, and the fault point can be found by this method.
④. Step voltage method When a DC high voltage pulse signal is applied between the fault phase and the ground, the direction of the step voltage on both sides of the fault point is opposite, and the fault point can be found by this method. The advantage of this method is that it can indicate the direction of the fault point, which is highly instructive to testers; however, this method can only find open faults with damaged sheaths of directly buried cables, and cannot find closed faults and faults of non-direct buried cables. Open fault. For faulty cables with damaged sheaths, due to the formation of multi-point discharge channels between the armor and the ground, the step voltage method may find multiple step voltage mutation points, which need to be eliminated.
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