NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
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NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Author: Noyafa–Cable Tester Suppliers
Power cables are equipment buried in the ground. Under normal circumstances, the soil layer protects the cables. However, once a fault occurs, it is very difficult to find, it takes a lot of time, and it is a great waste of manpower and material resources. In this case, cable fault detection equipment, such as a power cable fault tester, is required.
The initial testing method of common fault cables is divided into control loop bridge balance method, bottom pressure single pulse reflection surface method, and flash detector method. A suitable cable fault detector can accurately measure and calculate the distance between the common fault point and the test case and the relative path position of the common fault point by using the technical documents of the cable line. There are three key methods of initial measurement: control loop bridge balance method, bottom pressure single-pulse reflector method and flash detector method. The method of improving the sensitivity of the galvanometer can be to modify the DC amplifier before the galvanometer, but the gain value of the amplifier is too high, which will cause serious zero drift and cause the bridge to fail to balance.
The working voltage of the switching power supply of the rising bridge must be relative to the compressive strength of the insulating layer of the bridge body to the ground, and the safety precautions of the maintenance and actual operators shall be adopted. When the working voltage of the switching power supply rises to a certain value, the common fault resistors are generally the main The performance is unstable. If the resistance of the ground wire is suddenly reduced to zero, the high voltage will be added to the bridge and the galvanometer will be damaged. Common power cable fault tester usage. The characteristics and regulations of the bridge method are: it is only suitable for measuring the downtime of the server in the cable line. If there are many other common fault points in the line, it cannot be used.
The less jumper wires at the other end of the cable line are, the higher the cross-section should be close to the cross-section of the electrical conductor of the cable line, and the connection should be tightened so that the contact resistance is close to zero. When raising the experimental working voltage to test the fault of the high-resistor grounding device, it must be very safe to prompt the problem. After using the common fault burn-through equipment to convert the flashover common fault into the common fault of the grounding device, it is necessary to use the power bridge method to measure immediately, so as to prevent the common fault point from being closed again due to the repair of the insulation layer.
In addition, it is not necessary to make the common fault ground wire flame retardant too low to prevent the difficulty of producing too little sound when using the precise measurement point method. The bottom pressure single-pulse reflector method, commonly known as the single-pulse method, is the basic principle of using the differential signal to spread in the cable line when it encounters the wave impedance mismatch point to cause the radio wave reflector. The single-pulse wave reflection is measured on a digital oscilloscope. The surface time and cable wave speed are used to determine the distance between the fault points of the cable. In general, the characteristic impedance of the cable line does not match the point. Except for the disconnection of the electrical conductor (lead), short-circuit fault and common faults of the grounding device, the characteristic impedance is also asymmetrical at the point where the cable joint and the cable pass over the metal material pipeline, etc. It will also cause the reflection surface of the wave, so be careful to identify it when testing.
Especially when the resistance value of the ground wire exceeds about 2 to 3 times of the wave impedance of the cable, the fluctuation amplitude of the reflection surface is not large, and it is impossible to identify common fault points. Single-pulse method* is suitable for detecting common faults of disconnection, and it is also suitable for detecting cable faults with ground wire resistance lower than 100Ω.
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