What is the method of finding the cable failure point?

  Direct short-circuit or disconnection faults can be directly measured and judged by a multimeter, which means that for non-direct short-circuit and ground faults, the insulation resistance between the core wires or the insulation resistance of the core wires to ground can be measured by a megaohmmeter, and the type of fault can be determined according to its resistance.After the type of fault is determined, finding the point of failure is not an easy task. Based on the author's experience, the following describes several methods of finding the point of failure.

  1. How to find the cable failure point

  (1) Sound measurement method: The so-called sound measurement method is to find the sound of the discharge of the faulty cable. This method is more effective for the flashover discharge of the insulating layer of the core wire of the high-voltage cable.The equipment used in this method is a DC withstand voltage testing machine.At the fault place, the cable core discharges the insulating layer to produce a ”Zi, Zi" spark discharge sound. For the exposed cable, it can be directly found by hearing. If it is an underground cable, the direction of the cable must first be determined and marked, and then when the noise is minimal, audio amplification equipment such as deaf hearing aids or medical stethoscopes can be used to find it.When searching, keep the pickup close to the ground and move slowly along the direction of the cable. When you hear the loudest discharge sound of “Zi, Zi”, this is the point of failure.Safety must be paid attention to when using this method, and special personnel should be set up at the end of the test equipment and the end of the cable to monitor.

  (2) Bridge method: The bridge method is to use a two-arm bridge to measure the DC resistance of the cable core, and then accurately measure the actual length of the cable, and calculate the point of failure according to the proportional relationship between the length of the cable and the resistance.This method generally has a judgment error of not more than 3m for faults with a direct short circuit between the cable cores or a contact resistance of less than 1Ω at the short-circuit point. For faults with a contact resistance of greater than 1Ω at the point of failure, the method of increasing the voltage burn-through can be used to reduce the resistance to below 1Ω, and then measure it according to this method.

  The measurement steps are as follows：

  ①The battery E is first connected to the b and c phase core lines, and then a comparison wire S of equal length to the faulty cable is laid on the ground. The wire should be bare copper wire or bare aluminum wire, and its cross-section should be equal. There can be no intermediate joints.

  ②The negative electrode of the microvolt meter is grounded, and the positive electrode is connected to a longer soft wire. The other end of the wire requires full contact when sliding on the laid comparison wire.Recommended products: Power cable

  ③Close the knife switch K and slide the end of the soft wire on the comparison wire. When the microvolt meter indicates zero, the position is the position of the cable failure point.