Due to the different nature of the cable fault, only different detection methods can be used for different fault properties. Therefore, before detecting the point of failure, first determine the nature of the fault and the cable laying status, location and length of the necessary technical reference materials, which helps to quickly and accurately identify the location of the point of failure.
1, to determine the nature of the fault
The most common method is to use a megger (using an intrinsically safe megger in the downhole). In the case of the other end of the core is fully open, the measurement of the core and the core to the ground insulation resistance, such as cable core to ground or phase short circuit. Note that the needle is zero, and the other end of the cable in the case of short-circuit, if broken, megger pointer to infinity.
2, fault detection method
Usually there are bridge method, pulse method, oscilloscope method, induction method, sound measurement method and so on. For details, see Chapter 14, Chapter 5, Power Cable Fault Test, for coal mine cables, KDLZ-1 mine cable fault tester is more applicable. It can be used in mines where the dust explosion is dangerous. Can detect mine power cable short circuit, grounding and disconnection of the fault location. However, it is difficult to detect the fault point of shielded rubber sheathed flexible cable and armored cable, which can not detect the high-resistance ground fault point, but also by the environment, The influence of the scattered current, the accuracy of detecting the fault point is affected. KDLZ-1 mine cable fault tester consists of audio generator, audio receiver, inductive probe, capacitive probe. Inductive probes are used for short-circuit and phase-to-phase short-circuit measurements. Capacitive probes are used for cable breakage measurements. Detection of fault location deviation of less than ± 20 cm, detection of fault cable length of 300m. When measuring the probe into a probe, the short-circuit two-phase or relative to the two terminals connected to the transmitter output of the two ends, the transmitter output through the fault cable into a closed loop, through the wire around Frequency of 825Hz alternating magnetic field. The inductive probe is composed of a coil wound on an electromagnetic rod. The magnetic field lines generate an induced electromotive force on the coil. The sensor is amplified by the receiver. When the probe moves along the cable line, there is a sound on the headphones. In the fault point after the rapid decline to silent, meter pointer swing amplitude is small or even swing. The measurement of the disconnection is the use of power lines through the capacitive probe to focus on the earth, for which the receiver sound at the break at the maximum, after the rapid decline to zero.