List of Fault Finding and Detection Methods for Low Voltage Cables

Generally, the radiation path of high-voltage cable is easy to determine, but the high-voltage cable needs to be filled with sand bricks to be deeply buried. Its fault point is difficult to find. The radiation length of low-voltage cable is short, the radiation is random and the path is unclear. The following small series will introduce the fault finding and detection methods of low-voltage cables. You can simply understand. In order to solve the problem of low-voltage cable fault, researchers have developed and produced a cable fault tester based on the principle of impulse flash method. In order to find and detect the fault of low-voltage cable, first measure the distance with rangefinder. In fact, first judge whether the cable fault is high resistance, low resistance or grounding, and adopt different test methods according to this condition. If it is a ground fault, the low-voltage pulse method of the rangefinder is directly used to measure the distance; If it is a high resistance fault, the high-voltage impulse discharge method should be used to measure the distance. When using the high-voltage impulse discharge method to measure the distance, there are many auxiliary equipment: such as high-voltage pulse capacitor, discharge ball, current limiting resistance, inductive coil and signal sampler. The operation is troublesome, unsafe and dangerous. What is more cumbersome is to analyze the sampling waveform, The knowledge requirements of testers are relatively high. The second step is to find the path (this step can be omitted if the path is clear). When finding the path, add a signal (path signal generator) to the cable, and then the receiver receives the signal. Walk along the path with the signal once to determine the path of the cable. However, the range of this path is about 1-2 meters, which is not particularly accurate. The third step is to accurately locate according to the measured distance. It is based on the sound generated by ignition and discharge. When a loud sound is heard from the headset of the pointing instrument, that is, the location of the fault point is found. Due to listening to the sound, it takes a lot of time to find it due to the influence of environmental noise. Sometimes it can't be found until the evening. When it comes to cross-linked cables, it takes more time. Generally, the sound of internal discharge of cross-linked cables is very small. After almost no hearing, it is only measured. Therefore, this method can solve most of the power cable faults with oil impregnated paper as insulating material. For the cable faults with crosslinked material and polyethylene material as insulating material in recent years, the test effect is not ideal, because the sound generated by ignition and discharge is often very small (the cable skin is not damaged, but the internal discharge of the cable), In this case, only other methods can be used to solve it. We know that the insulation requirements of low-voltage cables are low, and the current is large during operation, which has obvious characteristics after failure. It is specifically classified as follows: class I fault: the whole cable is burned out or a phase is burned out. This fault causes the current relay on the distribution cabinet to act, and the cable is seriously damaged at the fault. Class II fault: each phase of the cable is short circuited. Similarly, this kind of fault causes the current relay and voltage relay on the distribution cabinet to act, and the cable is seriously damaged at the fault point (possibly caused by external force). Class III fault: the cable has only one phase open circuit, the current relay acts, and the damage at the fault point is light but obvious. It may be that the phase current is too large or caused by the cable quality. Four types of faults: internal short circuit of cable, no trace can be seen on the surface. Such faults are generally caused by cable quality, which is relatively rare.

List of Fault Finding and Detection Methods for Low Voltage Cables 1

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5 Reasons a Voltage Detector Pen Is Good for You
A voltage detector is a quick and inexpensive method to check the presence of voltage in an AC circuit, switch or socket without actually working with it. Also known as a voltage rod, rod, sniffer or pin, a voltage detector clings to a shirt pocket and beeps or glows when it detects voltage in a conductive part of the insulation.Voltage detectors are used to repair electrical circuits, detect live neutral wires and in other situations where you need to verify the presence of electric current. These types of voltage detectors are designed for the non-contact detection of electrical circuits in residential, commercial and industrial buildings. Random contact with live electrical conductors is no problem, and the detector evaluates the voltage level in the electrical safety category for which it is used.The voltage tester Klein Tools ET40 is ideal for checking regular electrical cables, door bell sockets, lights and other devices. It has functions for displaying positive and negative DC polarity and is able to detect DC voltage currents as low as 1.5 V. In addition to detecting standard voltages and low voltages, voltage detectors and LED testers can also detect rated voltages.A good voltage tester not only saves you time, but also gives you the certainty that your electricity prices are normal. The best voltage detector pins operate in a wide voltage range and are able to provide acoustic and acoustic feedback when detecting voltage. They are small enough to be transported and provide a precise reading that tells the user whether voltage is present or not.Reinforced electronic testers (also called electrical testers, pins and voltage detectors) rely on capacitive currents to detect changes in the electric field of an energy-charged object. Non-contact voltage testers (test pins, voltage sensors, voltage testers and pins they know) are the safest way to ensure that an electrical conductor has no voltage without touching it or suffering an electric shock. They work by detecting changes in an electric field surrounding an object conducting alternating or alternating current.Non-contact testers allow you to check the voltage of a wire or device without having to touch the wire or part. A voltage tester can be used to test the presence of voltage when a multimeter cannot detect it and to measure and display the exact amount of available voltage. These testers are designed to detect the main voltage and do not provide any indication of low voltage control circuits used in the bells or HVAC controls.A further limitation is that DC voltage can not be detected with this method because DC currents do not flow in a uniform state through capacitors and non-contact testers that detect electrical fields cannot be activated. You cannot detect voltage through shielded or armoured cables, and this is a basic limitation due to the Faraday cage effect. A TONG or AMmeter detects changes in magnetic fields, while a detector uses current flowing through the wire in question, and it senses alternating electric fields emitted by AC conductors.Given the variety of products in the contactless voltage tester category, you can expect different types of NCVTs, but you can imagine that there are more contactless DC voltage testers and contactless DC voltage testers than there are regular DC testers on the market. Remember to use a quality insulation resistance tester when you need to measure the insulation around your circuit. You want a non-contact voltage tester that comes with a hook so that you can put it in your shirt pocket.I call it the voltage sniffer, but the technical name for it is the capacitive voltage sensor. It is supplied with an alligator clip, which is interchangeable with test cables, and a holster to keep it handy. It uses black magic to determine whether wires are live or not, and it is 100% reliable at all times.
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