Four practical methods for measuring cable faults

First, the type of cable fault and judgment

Whether it is high-voltage cables or low-voltage cables, faults often occur during construction, installation, and operation because of short-circuit, overloaded operation, insulation aging, or external damage. The cable fault is divided into three types: grounding, short circuit, and disconnection. Three-core cable fault types mainly include the following aspects: one-core or two-core contact; two-phase core-line short circuit; three-phase core line completely short-circuit; one-phase core wire breakage or polyphase breakage. For direct short circuit or disconnection fault judgment can be directly measured with a multimeter, and a short circuit for the non-direct connection pool faults with megger telemetry between the core wire or the insulation resistance of the insulation resistance to ground, the resistance may be determined according to the type of fault.

Second, the cable fault point search method

1. Sound measurement method The so-called sound measurement method is based on the sound of faulty cable discharge. This method is more effective for high-voltage cable cores for insulation layer flashover discharge. The equipment used in this method is a DC voltage tester. The circuit connection is shown in Fig. 1, where SYB is a high voltage test transformer, C is a high voltage capacitor, ZL is a high voltage rectifier silicon stack, R is a current limiting resistor, Q is the discharge ball gap, and L is the cable core. When the capacitor C is charged to a certain voltage value, the ball gap discharges the cable fault core wire. At the fault, the cable core wire discharges the insulating layer to generate a sparking discharge sound of “nose and nourishment”. When the noise noise is minimal, use the An audio amplification device such as an earwax hearing aid or a medical stethoscope is used for searching. When searching, pick up the pickup close to the ground and slowly move along the direction of the cable. When you hear the sound of the “noisy and noisy” discharge, it is the point of failure. Use this method must pay attention to safety, in the end of the test equipment and the end of the cable should be set up to monitor.

2. The bridge method bridge method is to measure the DC resistance value of the cable core by two-arm bridge, then accurately measure the actual length of the cable, and calculate the fault point according to the proportional relationship between the length of the cable and the resistance. In this method, the error for the direct short-circuit or short-circuit point contact resistance between cable cores is less than 1Ω, and the error is generally not more than 3m. For faults with contact resistance greater than 1Ω at the fault point, the resistance can be reduced to 1Ω by increasing the voltage through burning. Below, measure again according to this method.