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–Cable Length Tester
After the rough measurement of the common fault cables, the approximate location of the common fault points can be found according to the distance and path of the common faults. However, due to factors such as complicated underground cable laying conditions, there may be a certain error in the distance between the rough measurement point and the specific common fault point. After the rough measurement of the common fault cables, the approximate location of the common fault points can be found according to the distance and path of the common faults.
However, due to factors such as complicated underground cable laying conditions, there may be a certain error in the distance between the rough measurement point and the specific common fault point. The manufacturer of the cable identification instrument pointed out that in order to find this position better and accurately, it is necessary to carry out accurate selection of common faults. (1) Shock discharge acoustic measurement method (acoustic measurement method for short): It uses DC high-voltage equipment to charge and store energy to the capacitor. When the voltage reaches a certain value, the ball gap breaks down, and the energy on the device and the capacitor passes through the ball gap. Discharge at the fault point of the cable produces mechanical vibration and sound waves, which are distinguished by the human ear or the hearing of the equipment.
Discharges with high energy can be identified on the ground, while those with low energy need to use a pickup device with higher sensitivity to find the location where the discharge sound is the loudest. This method is mainly used for the fixed point of high-resistance faults of power cables. (2) Audio signal method: If a low resistance fault occurs, it is difficult or impossible to hear the discharge sound detected by the acoustic measurement method.
At this time, the audio signal method can be used to detect the change of the magnetic field on the ground, and the position of the fault point can be detected according to the change of the sound in the earphone. The signal received by the audio signal just above the fault point will suddenly increase, and the signal will obviously weaken or disappear after the fault point, and the strongest audio signal is the fault point. (3) Acoustic-magnetic synchronization method: The basic principle is to apply an impact DC high voltage to the cable to discharge the fault point, and at the moment of discharge, an induced circulating current is formed in the circuit formed by the metal sheath of the cable and the ground, thereby generating a pulsed magnetic field around the cable.
The instrument receives the pulsed magnetic field signal and the discharge sound signal sent from the fault point, and the point with the smallest time interval between the two detected acoustic and magnetic signals is the fault point. The advantages of this method are that the fixed-point accuracy is high, the anti-environmental interference is strong, and the signal is easy to understand and distinguish. (4) Step voltage method: Step voltage method, by adding a DC high voltage pulse signal between the fault phase and the ground, and using a voltmeter near the fault point to monitor the magnitude and direction of the step voltage mutation between the two points during discharge. Find the point of failure.
The advantage of this method is that it can indicate the direction of the fault point; the disadvantage is that it can only find open faults with damaged sheaths of directly buried cables, and is not suitable for finding faults of closed or non-direct buried cables. Cable identification instrument manufacturers point out that the distance measurement of power cable faults is a very technical and empirical work. Its theoretical basis is relatively mature, but it is closely related to the field environment, system operation mode, etc., and the experience of fault location and location is a slow accumulation process.
The causes and phenomena of faults vary widely, all of which need to be based on the mastery of theoretical knowledge, flexible application of the learned theory, combined with rich on-site practical experience, analysis of the sudden inflection point of the waveform, in order to quickly and accurately find out the cable fault and eliminate the line in time The power supply can be quickly restored in case of failure, and the economic loss can be minimized as much as possible. The above is the common fault pinpointing method analyzed and summarized by cable identification instrument manufacturers, I hope it can be helpful to everyone.
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