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How is lightning applied to the underground? And why are lightning strikes in closed wells?
Expert studies have shown that lightning can be introduced into the well through direct lightning strikes, electrostatic induction, electromagnetic induction and electromagnetic radiation. Lightning has a large amount of pulsed electromagnetic waves. When the mine is in the electric radiation field, various conductors (such as lightning rods) act as receiving antennas, so that lightning is transmitted to the well. Meanwhile lightning can also track the mine iron, iron pipes, wire armored cable, wire communications, and other overhead line directly from the ground is introduced downhole. When lightning is transmitted to generate sparks, it is easy to cause gas explosion, coal dust explosion and electric fire accident.
The conditions of lightning explosion caused by lightning, first, the lightning must have enough energy, the second is that there must be a conductor to extend the spark, and the third is to have the corresponding gas concentration to reach the explosion limit.
The countermeasures against lightning are mainly to use venting, intercepting and grooming. The means adopted are mainly grounding, insulation, pressure equalization and shielding. In order to prevent ground lightning and underground fires, coal dust and fires, the following regulations must be observed:
1. When the underground power supply line (including the motor frame line) is introduced via the overhead line, a lightning protection device must be installed at the access point. The grounding resistance of the installed lightning arrester shall not exceed 5Ω.
Second, the metal sheath directly into the well from the ground rail, pipe, armored cable, must be grounded metallic body in the vicinity of the wellhead least two electrically grounded cathode electrode is not more than 5 [Omega, two grounding The distance should be greater than 20m.
Third, the communication line must be equipped with fuses and lightning protection devices at the well. The grounding resistance of the arrester must not exceed 1Ω.
4. For wire rope hoists and wire rope cans for lifting cages, the winch hoist and steel rope must be reliably grounded near the wellhead, and the grounding resistance must not exceed 4 Ω.
5. In order to prevent the lightning rod (wire) from receiving the lightning antenna, the wellhead should not be equipped with a needle arrester. It is better to use a valve-type arrester or other means of lightning protection.
Sixth, strengthen mine ventilation management and watering and dust reduction to prevent gas and coal dust accumulation.
7. Before the abandoned wells or goafs are closed, all metal conductors in the roadway or in the enclosed area shall be removed to eliminate the passages causing incoming lightning and the lines generating sparks.
Mine lightning protection
2000 at 14:20 on July 1, Yichun City, Jiangxi Province Yuanzhou West Village town silkworm over a thunderstorm, a bolt of lightning suddenly, I heard a clap of thunder falling to the ground, then get rid of cattle litter the village under coal mine came a muffled The smoke at the wellhead was rolling, and all the six miners working in the underground were killed. It was later discovered that this was a mine gas explosion accident caused by a lightning strike.