For direct short circuit or broken cable fault, the multimeter can be used for direct measurement and judgment; For indirect short-circuit cable fault and grounding cable fault, use a megger to telemeter the insulation resistance between core wires or the insulation resistance between core wires and ground, and judge the cable fault type according to its resistance value. The following describes the method of cable fault finding: zero potential method. Zero potential method is also known as potential comparison method. It is suitable for short cable core to ground fault. This method is simple and accurate, and does not need precision instruments and complex calculation. The measurement principle is as follows: connect the cable fault core wire in parallel with the comparison wire of the same length. When applying voltage ve at both ends of B and C, it is equivalent to connecting the power supply at both ends of two parallel uniform resistance wires. At this time, the potential difference between any point on one resistance wire and the corresponding point on the other resistance wire must be zero. On the contrary, the two points with zero potential difference must be the corresponding points. Because the negative pole of the micro voltmeter is grounded and equipotential with the cable fault point, when the positive pole of the micro voltmeter moves to the point when the indicated value is zero on the comparison wire, it is equipotential with the cable fault point, that is, the corresponding point of the cable fault point. S refers to single-phase knife switch, e refers to 6e battery or 4 No. 1 dry batteries, and G refers to DC microvolt meter. The measurement steps are as follows: 1) connect battery E on phase B and C core lines, and then lay a comparison conductor s with the same length as the fault cable on the ground. The conductor shall be bare copper wire or bare aluminum wire, with equal cross section and no intermediate joint. 2) The negative pole of the micro voltmeter shall be grounded, and the positive pole shall be connected with a long flexible conductor. The other end of the conductor shall be fully contacted when sliding on the laid comparison conductor. 3) Close the knife switch s, slide the end of the flexible conductor on the comparison conductor, and the position when the microvolt meter indicates zero is the position of the cable fault point. High voltage bridge method high voltage bridge method is to measure the DC resistance of cable core with double arm bridge, then accurately measure the actual length of cable, and calculate the cable fault point according to the positive proportional relationship between cable length and resistance. For direct short circuit between cable cores or short circuit point, the contact resistance is less than 1 & omega; The judgment error is generally not greater than 3m, and the contact resistance at the fault point is greater than 1 & omega; The resistance can be reduced to 1 & Omega by increasing the voltage and burning through; Next, measure according to this method. When measuring the circuit, first measure the resistance R1 between core wires a and B, R1 = 2RX R, where Rx is the phase resistance value from phase a or phase B to the cable fault point, which is only the contact resistance of the short contact. Then move the bridge to the other end of the cable and measure the DC resistance R2 between A1 and B1 core wires, then R2 = 2R (l-x) r, and R (l-x) is the phase resistance from A1 phase or B1 phase core wire to the cable fault point. After measuring R1 and R2, short circuit B1 and C1 according to the circuit shown in Figure 3, and measure the DC resistance value between B and C core wires, then 1 / 2 of the organization is the resistance value of each phase core wire, expressed by RL, RL = RX R (l-x), from which the contact resistance value of the fault point can be obtained: r = R1, r2-2rl table. Therefore, the resistance value of the core wires on both sides of the fault point can be expressed by the following formula: RX = (r1-r) / 2, R (l-x) = (r2-r) /2. After the three values of Rx, R (l-x) and RL are determined, the distance X or (l-x) between the fault point and the cable end can be calculated according to the proportional formula: x = (Rx / RL) l, (l-x) = (R (L-2) At the end of the cable, measure the capacitance currents IA1, IB2 and IC3 of the core wire of each phase to check the capacitance ratio between the intact core wire and the broken core wire, and preliminarily judge the approximate point of the broken wire distance. According to the capacitance calculation formula C = I / (2 & PI; Fu), when the positive voltage U and frequency f do not change, C is directly proportional to I. because the frequency of power frequency voltage is f (frequency) Constant, as long as the applied voltage is kept constant during measurement, the ratio of capacitance to current is the ratio of capacitance. If the total length of the cable is l and the distance of the core wire breaking point is x, then IA / ic = L / x, x = (IC / IA) 50. In the process of measurement, as long as the voltage remains unchanged, the reading of ammeter is accurate and the total length of cable is measured accurately, the measurement error is relatively small. The so-called sound measurement method is to find out according to the discharge sound of faulty cable. This method is more effective for the flashover discharge of high-voltage cable core to insulating layer. The equipment used in this method is DC withstand voltage tester. TB is high-voltage test Transformer, C refers to high-voltage capacitor, ve refers to high-voltage rectifier silicon stack, R refers to current limiting resistance, Q refers to discharge ball gap, and l refers to cable core. When capacitor C is charged to a certain voltage value, the ball gap discharges to the cable fault core, and the cable core discharges to the insulating layer at the cable fault, producing a loud and loud spark discharge sound. For open laying cables, it can be found directly by hearing. If it is buried electricity For cable, first determine and mark the cable direction. When searching, put the pickup close to the ground and move slowly along the cable direction. When the sound of Zi and Zi discharge is the largest, this is the cable fault point. Pay attention to safety when using this method, and assign special personnel to monitor at the end of the test equipment and the end of the cable. The cable fault locator produced by our company can not only measure the sound, but also To detect the magnetic signal, the signal strength is displayed visually and synchronously, which can locate the cable fault point faster and more accurately.