Author: Noyafa–CCTV Tester
Analysis of the form of breakdown of cable faults The breakdown of cable faults can basically be divided into two forms: electrical breakdown and thermal breakdown: Electrical breakdown is that when the voltage is high and the field strength is large enough, there is a small amount of free electrons in the medium. Under the action of the electric field, the collision and dissociation are generated, and the analysis of the form of cable breakdown breakdown can basically be divided into two forms: electrical breakdown and thermal breakdown: There is a small amount of free electrons in the medium, which will collide and dissociate under the action of the electric field. The free electrons collide with neutral molecules, making them excited and free to generate new electrons and positive ions. After these electrons and positive ions obtain the energy of the electric field, they will collide with other neutral molecules. collide with each other, this process continues to develop, making the electron flow in the medium“avalanche”Intensified, causing the insulating medium to break down, forming a conductive channel, and the fault point was instantly short-circuited by a strong electron flow. In the cable fault test, we use DC high voltage or impulse high voltage to make the cable fault breakdown, and the action time is very short, which is an electrical breakdown. Thermal breakdown is that the temperature of the insulating medium increases due to the heat generated by the dielectric loss under the action of the electric field. If the calorific value is greater than the heat radiated to the surrounding medium, the temperature will continue to rise. , causing the insulating medium to burn, crack or partially fuse, and finally lead to breakdown.
The thermal breakdown voltage has a long action time and generally occurs during the operation of the cable. In the cable fault test, under the action of DC or impact high voltage, an arc is generated in the discharge channel, and a breakdown phenomenon occurs. Each breakdown will further damage the insulating medium and further expand the discharge channel. Generally speaking, the resistance at the fault point will be reduced, and the critical breakdown voltage will be reduced.
In some special cases, such as when the fault point is seriously damp, the heat generated by the discharge arc at the fault point evaporates the water at the fault point, which plays a drying role, and the insulation resistance of the fault point increases.
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