In the wire and cable industry, we can often hear the word "insulation breakdown", and it occurs more in the use of power cable. So what does the meaning of insulation breakdown of power cable mean? The cable of the electrical complete equipment manufacturer tells you:
First, it should be understood that discharge is the reason for the insulation breakdown of power cable
Discharge refers to the transfer of electronic energy between two conductors when the performance of insulation materials decreases. For example, the ignition between high voltage wire and ground wire is discharge. Complete discharge means that the complete arc channel is formed between two electrodes in the instantaneous discharge.
In addition to the above mentioned discharge, there are also special discharge cases - partial discharge
There are two main cases of partial discharge
1. there is insulation between two conductors. When there is defect in the insulation material, such as impurities, voids, tip of conductor, etc., the electric field will be differentiated inside the insulation, which will cause pulse discharge in the insulation.
2. corona generated by external discharge is also a kind of partial discharge. Air insulation is provided between high potential and grounding. When the electric field around the conductor is specially concentrated at a certain point, such as the burr of the conductor, pulse discharge is generated in the air, and no short circuit to ground is formed to form corona.
Characteristics of partial discharge
Partial discharge also has the basic characteristics of discharge, that is, the transfer of electronic energy. Because of the small discharge energy and the barrier of insulating materials, there is no complete arc channel between the two electrodes. Once such channels appear, the partial discharge will be intensified, and the short circuit discharge fault will occur until the two poles are completely connected.
The cause of partial discharge
The air gap in the main insulation will cause partial discharge. Because the relative dielectric constant of air gap is far less than cable insulation, under the action of power frequency electric field, the air gap should bear a large electric field intensity. Tens of millions of partial discharge, with the multiple discharge of air gap, the air gap path is expanding, and the discharge amount gradually increases until breakdown occurs, which causes cable damage.
The impurity in the main insulation causes partial discharge. The breakdown strength of impurities is much smaller than that of insulating materials. Under the action of electric field, the impurities first discharge, carbonize and gasify, and generate air gap, which leads to partial discharge.
導體的尖 端、毛刺會引起局部放電。由于尖 端會使電場強度增加，尖 端周圍的絕緣材料先發生放電，進而發展成擊穿，這就是我們常說的尖 端效應。
The tip and burr of conductor can cause partial discharge. Because the tip increases the electric field strength, the insulation around the tip first discharges and then develops into breakdown, which is what we often call the tip effect.
Above are some factors that cause insulation breakdown of power cable. In the laying and use of cables, more attention should be paid to. If insulation breakdown is found, we can refer to the above factors to find out the problem as soon as possible.