Author: Noyafa–CCTV Tester
Question: Analysis of cable fault location and test application experience Answer: 1. Acoustic magnetic method: pulsed high voltage is used to make power cable fault point and discharge, cable fault gap discharge to produce mechanical fault, repair high resistance fault and flashover fault power cable. Acoustic and magnetic questions: cable fault location and test application empirical analysis Answers: 1. Acoustic and magnetic method: pulsed high voltage is used to make power cable fault click and discharge, cable fault gap discharge to produce mechanical fault, repair high resistance fault and flashover fault power cable. The acousto-magnetic method is based on the principle that the velocities of the acoustic signal and the magnetic field signal are different.
The instrument probe detects the time difference between the acoustic signal and the magnetic field signal to determine the exact point of failure. 2. Audio induction method: It is used for short-circuit faults of power lines. Since there is no discharge sound, the acousto-magnetic method cannot be used. Only the audio induction method can be used to determine the fault point. The audio sensing method uses an audio signal generator to connect audio current between shorted cores of a power cable, and the power cable emits electromagnetic waves.
On the ground near the fault point of the power cable, the probe (induction coil) is used to track the signal of the power cable under test to receive the change of the electromagnetic field, amplify the signal and send it to the earphone or indicator to detect the change of the signal until the signal disappears . The audio signal is strongest at the point of failure of the power cable. 1. The cable must be required to provide complete cable information (length, path reservation, joint location, etc.).
2. It is easier to pre-locate the main insulation fault, and it is difficult to precisely locate it; on the contrary, it is difficult to pre-locate the sheath failure, and the precise location (step voltage method) is very accurate and easy. In special cases F (when insulation and outer sheath failures are common) they can be combined. 3. When building low-voltage cable connectors, the ground wire connection is not standardized.
When testing, pay attention to cable grounding and grounding. When no obvious waveform is detected at one end of the cable, change the other end or increase the arc current and measure again for a better waveform. 4. When the measured cable is long and no waveform is detected at the predetermined position, the pulse voltage can be increased or the trigger delay can be adjusted to obtain the waveform.
For intermittent faults, when the surge voltage cannot be decomposed, it can be decomposed by the traditional DC withstand voltage test. 5. Pre-positioning errors include: a. Instrument error, constant; b. Measurement error, the impact is greater, should pay attention to whether there are reserved rings at both ends of the cable; c.
The error of the wave speed value is incorrect and should be calculated according to the length of the cable; d. Waveform judgment errors depend on instrument performance and tester experience.
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