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How is arc light formed?
Source: | Author:hkwa49fa3 | Published time: 2019-07-01 | 1439 Views | Share:
Arc short circuit fire: if the two electrodes are contacted and then pulled open to establish an arc, it is only 20V to maintain the 10mm long arc. That is to say, as long as the first contact, and then separated, it is likely to generate an arc with a high local temperature and become a source of ignition.
The different parts of the arc can be divided into an arc between the charged conductors, an arc between the live conductor and the ground, and creepage of the insulating surface.
1) Arc-induced short-circuit fire between live conductors: There are two possibilities when it comes to short-circuit fires. One is the high temperature caused by short-circuit current when two conductors (such as phase and neutral) are in contact, causing the contact metal to melt. The metal then melts into a process of shrinkage and disengagement, in which case an arc may be established. “If the insulation level of the line is seriously degraded, the transient over-voltage generated by lightning or the grid fault may break the deteriorated line insulation to establish an arc.” “ The fire hazard of arc short circuit is much greater than the above metal short circuit. "
2) Ground fault arc ignition: Since "the probability of ground fault is much greater than the short circuit between the live conductors", "the fire caused by the ground fault arc is much more than the arc fire between the live conductors". This is because "in the electric line construction, there is no friction between the insulated outer skin of the live conductor when the steel wire is drawn through the steel pipe, but the friction between the insulated outer skin of the live conductor and the steel pipe causes the insulation to be thin or damaged. In addition, when a lightning strike occurs, a transient electromagnetic field appears on the ground, which induces a transient overvoltage on the electrical line. At this time, “the transient overvoltage induced on the core is basically the same, and the cable ladder is grounded due to grounding.", therefore, the potential difference between the core and the ground is large. From the two aspects of friction and potential difference, the grounding fault arc ignition rate is naturally high.
3) Creepy fire: Creepage means that the arc is not an arc built up in the air gap, but an arc that appears on the insulation surface of the equipment. For example, one or more phase pins and PE wire pins on the insulating surface of the power plug may have creepage on the insulating surface between them.

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