Author: Noyafa–CCTV Tester
The method of cable fault inspection and measurement For direct short-circuit or broken cable faults, a multimeter can be used to directly measure and judge; for non-direct short-circuit cable faults and grounding cable faults, use a megohmmeter to remotely measure the insulation resistance between core wires or the insulation resistance of core wires to ground. , One cable fault inspection and measurement method For direct short-circuit or disconnected cable faults, a multimeter can be used to directly measure and judge; for non-direct short-circuit cable faults and grounding cable faults, use a megohmmeter to remotely measure the insulation resistance between core wires or core wire-to-ground. Insulation resistance, the type of cable fault can be judged according to its resistance value. The following introduces the method of cable fault finding: Zero potential method Zero potential method is also the potential comparison method. It is suitable for the ground fault of the cable core with short length. Using this method is simple and accurate to measure, and does not require precise instruments and complex calculations. The measurement principle is as follows: connect the faulty core wire of the cable in parallel with the comparison wire of the same length, and when the voltage VE is applied at both ends of b and c, it is equivalent to the power supply at both ends of the two parallel uniform resistance wires. The potential difference between any point of and the corresponding point on the other resistance wire must be zero, on the contrary, the two points with zero potential difference must be corresponding points.
Because the negative pole of the microvoltmeter is grounded and has the same potential as the fault point of the cable, when the positive pole of the microvoltmeter moves on the comparison wire to the point where the indicated value is zero, the point is equipotential with the fault point of the cable, that is, the corresponding point of the fault point of the cable . High-voltage bridge method High-voltage bridge method is to measure the DC resistance value of the cable core wire with a double-arm bridge, and then accurately measure the actual length of the cable, and calculate the cable fault point according to the proportional relationship between the cable length and the resistance. This method is suitable for direct short-circuit between cable cores or short-circuit point contact resistance less than 1ΩThe fault of the fault, the judgment error is generally not more than 3m, and the contact resistance of the fault point is more than 1ΩIf the fault occurs, the resistance can be reduced to 1 by adding a high voltage to burn through.ΩHereinafter, measure again according to this method.
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