Hidden dangers and safety measures of electrical s

2022-08-11
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Hidden dangers of accidents in coal mine electrical system and safety measures

1 main hidden dangers of accidents in coal mine power supply system

electrical accidents that may be caused by defects in electrical equipment and facilities (improper selection, insufficient breaking capacity, cable overload, non flame retardant, etc.) include: power line pole fall, wire break, overload, short circuit, power failure, personnel electric shock, electrical equipment fire, electric spark, explosion-proof electrical equipment explosion, etc

1) lightning overvoltage and fire hazards. During thunderstorms, lightning strikes produce overvoltage, discharge sparks, or breakdown or even short circuit of equipment and cables. Sparks generated by discharge or short-circuit fire sources will ignite inflammables (cables, control lines, power oil, oil pollution, etc.) and cause a fire. Mechanical ventilation and smoke exhaust devices are not installed in the power transformation and distribution room and there are not enough fire-fighting equipment. It is difficult to deal with the accident, resulting in the expansion of the accident, resulting in the power failure, air suspension and shutdown of the whole mine

2) insufficient capacity of switch circuit breaker. Due to the small interrupting capacity of switches and circuit breakers, the short-circuit current cannot be broken, and a large amount of heat energy is generated due to the short-circuit fault instantly, which will burn the equipment and cables, causing fire accidents, causing power cuts, wind stops and production stops of some users or the whole mine, and in serious cases, it can cause casualties and property losses

3) the capacity of main transformer is insufficient, and the power line is defective. The capacity of the main transformer is insufficient. When one transformer has an accident, the other transformers cannot guarantee the power supply of the first and second level loads in the mine. The power line of the mine is not designed according to the local meteorological conditions. In case of severe weather such as strong wind, snow and icing, the line strength is insufficient, which is easy to cause pole collapse and line disconnection, resulting in the air stoppage and shutdown of the whole mine. The underground operators will speed up the upgrading of plastic granulator technology due to the air stoppage, which is life-threatening, causing property losses and casualties

4) relay protection device defect. If the relay protection device is not installed as required or unqualified backward and obsolete products are adopted, there will be skip tripping and misoperation, resulting in unreasonable power failure and expanding the scope of the accident

5) locking defect. The switch cabinet locking is not installed or fails, which is easy to cause misoperation, and the knife switch stops power transmission under the loaded state, resulting in a short circuit. Electric shock will occur when personnel enter the switch under the internal charged state

6) underground electric spark accident. ① Improper installation and maintenance of electrical equipment used underground may cause explosion failure (such as loose sealing of explosion-proof chamber/chamber, explosion-proof surface, sealing ring gap not meeting the requirements, etc.). When electric sparks are generated due to switch contact opening and closing or other reasons, gas may be ignited, causing fire or gas explosion accidents. ② Due to external force, the underground live cable is damaged, pulled off, and the cable insulation is reduced, which is easy to cause system short circuit, grounding, and electrical sparks. Electrical sparks may cause ignition of gas, causing fire or gas explosion accidents. ③ The protection of electrical equipment fails. In case of overcurrent, short circuit, grounding and other electrical accidents, the equipment and cables will be overloaded and overheated, causing electrical sparks, which may ignite gas and cause fire or gas explosion accidents

7) electric shock accident of underground personnel. ① Insulating gloves, insulating boots, electric testing pens and other products used by underground electricians during operation will not have the phenomenon of glass fiber reunion, the appliance is damaged, the degree of insulation is reduced, and the indication of electric testing pens is incorrect. ② The locking device is incomplete, invalid, the warning signs are unclear, and personnel enter by mistake. ③ The electrical protection device of the equipment fails, and the equipment and cable cannot be switched off and powered off due to overcurrent and overheating, resulting in the decline or damage of its insulation. ④ The grounding system is damaged, not reliably grounded, protective grounding fails, and the equipment shell and cable sheath are leaking electricity. ⑤ Live cleaning, live installation, live maintenance and live relocation of electromechanical equipment against regulations. ⑥ Failure to implement the power cut-off and transmission system or misoperation, wrong power cut-off and transmission, wrong identification of switches and cables, failure to implement the operation monitoring system, and failure to hang the "no power transmission when someone is working" sign. ⑦ There is no work ticket and safety measures, and the regulations and requirements on power failure, power inspection, discharge, etc. in high-voltage operation are not implemented

8) large area underground power failure accident. ① The cable in the shaft was not fixed firmly, and the cable fell into the shaft, resulting in a large area of underground power failure. ② When a short-circuit accident occurs to underground electrical equipment and cables, the electrical protection device refuses to operate or the action is not sensitive, resulting in skip tripping. ③ Double circuit parallel operation with normal separate operation violates regulations. When a short-circuit accident occurs in one section of bus power supply system, the other section of bus power supply system will be shut down at the same time, and the double circuit power will be cut off. ④ Areas or equipment that should use dual circuit power supply adopt single circuit power supply

9) lightning strike accident. ① The power supply line LED underground through the ground has imperfect lightning protection facilities or device failure. ② The pipelines and derricks entering the well from the ground are not installed at the wellhead or below, let's learn about the breaking strength test scheme of 1 milk silk tensile testing machine. Less than two centralized grounding devices are installed, which are poorly grounded. ③ It is a communication line developed and applied by Imperial University of England. The fuse and lightning protection device are not installed at the well entrance, or the device is poor

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