Due to the complicated production environment of the mine, the underground roadway is narrow, the air is humid, the working conditions are bad, and the electrical equipment and cables are susceptible to rolling and insulation damage. Therefore, a series of faults such as personal electric shock, electric leakage and short circuit are easily occurred in the underground. The long-term existence will cause the detonator to detonate in advance. Therefore, damage to electrical equipment and safety failure will not only affect the output, but also cause serious accidents such as gas explosion. Therefore, technical measures and protection measures must be taken to ensure personal and electrical. The safety of the equipment.
1 Safety accidents that may occur in underground electrical equipment
1.1 Grid current faults Any current flowing through an electrical device that exceeds the rated value is called an overcurrent. There are many causes of overcurrent, such as short circuit, overload, and single-phase operation of the motor. Whatever happened to a short circuit or overload the accident, will make electrical equipment or heating cable exceeds the allowable limit, causing damage to the insulation, or even cause a fire underground gas and coal dust fire or explosion.
1.2 Electric fire accidents The power supply line and electrical equipment are short-circuited between phases, and the electrical equipment is overloaded for a long time, which may cause the temperature rise of the current-carrying conductor to be too high, resulting in fire. Electric sparks and arcs can ignite insulating materials, wood supports, and gas dust, causing fires. The contact of the conductor connection is poor, the contact resistance is increased, and the local temperature rise caused by the current is often an important cause of fire. The cable junction box and the cable head are not high in quality due to the sealing process, and there is an air gap. When the moisture invades, the explosion of the heated gas causes an explosion accident and causes a fire. The insulating oil of electrical equipment is used in humid environment, the oil absorbs water, the insulation performance is degraded, and phase-to-phase short circuit may occur, causing oil to burn. Under the action of arc, the insulating oil can decompose the mixed gas containing hydrogen at high temperature. explosion. The downhole lighting incandescent lamp covers the coal dust, the heat dissipation is poor, and the temperature rises, causing the coal dust to ignite and causing a fire.
1.3 Electric shock and electric accidents Electric shock refers to the passage of electric current when a person touches a charged body or is close to a high-voltage charged body. The electric shock includes contact with the normal electrified part, electric shock, contact with the electric leakage part, electric shock, and no direct contact with the electric equipment. In order to prevent the occurrence of electric shock accidents, in the process of design, manufacture, use and maintenance of electrical equipment, it is necessary to strictly implement the relevant provisions of the "Safety Regulations for Coal Mines" and so that safe use of electricity is achieved.
1.4 Electrical equipment is out of explosion In the gas and coal dust explosion accidents, gas and coal dust accidents caused by the explosion of electrical equipment such as electric sparks account for a large proportion. In order to make the sparks or arcs and excessive heat generated by the electrical equipment in the normal working state and the fault state, the gas and coal dust in the mine are not ignited.
1.5 Grid leakage fault The relative humidity in the underground mine roadway is as high as 95%. The electrical equipment operating under this condition, although some special measures have been taken for its insulation, the leakage fault still occurs from time to time. In particular, some low-voltage cables in the mining area are often damaged by falling rocks or coal, which may cause electric leakage accidents.
2 Safety accident prevention measures
2.1 Main measures to prevent current faults The main measures to prevent current faults are: use overcurrent protection devices; use the maximum three-phase short-circuit current of the distribution network to verify the breaking capacity and dynamic thermal stability of the switchgear and the thermal stability of the cable. Use the minimum two-phase short-circuit current to verify the reliable action coefficient of the protection device; the over-current protection device used shall be regularly checked and adjusted according to the regulations; when the load changes, adjust the setting value of the over-current protection device in time. To ensure its reliability; strengthen daily maintenance and inspections.
2.2 Main measures to prevent electric fires The main measures to prevent electric fires are: correctly selecting and installing electrical equipment and power supply lines, and strengthening maintenance and repair during operation to prevent short-circuit faults and overload conditions; installing relay protection devices; Reasonable setting of various short-circuit protection devices to ensure their sensitivity and reliability; take appropriate fire prevention measures in places where electric fires may occur.
2.3 Main measures to prevent the explosion of electrical equipment The main measures to prevent the explosion of electrical equipment are: for power equipment such as switchgear and motor, explosion-proof enclosure can be used for explosion-proof, and the casing has sufficient strength, even if gas explosion occurs in the casing. Does not deform, and the flame that escapes from the gap outside the shell should be cooled enough to ignite the gas and coal dust outside the shell; use intrinsically safe circuits and equipment; use the power cut-off to make the electrical equipment in normal and faulty state The heat source or spark generated below will automatically cut off the power supply to achieve the purpose of explosion protection before it has caused the explosion in the wattage period; strictly follow the standards of explosion-proof electrical equipment, conduct daily inspections and patrol inspections.
2.4 Main measures to prevent electric shock The main measures to prevent electric shock are: make the human body unable to contact or approach the charged body; the underground electrical equipment must be provided with protective grounding; in the underground high and low voltage power supply system, install the leakage protection device; use a lower voltage level The laying of the underground cable is in compliance with the regulations and strengthens the management; the operation of high-voltage electrical equipment must comply with the safe operating procedures and use of security tools; the handle of the hand-held electrical equipment should be well insulated, the voltage must exceed 127V, and the voltage of the electrical equipment control loop must not be More than 36V.
2.5 Main measures to prevent leakage The main measures to prevent leakage are: the type of electrical equipment correctly selected by the underground power grid; the power supply system with neutral point insulation; the protective earthing measures; the leakage protection device acting on the switch trip; the high voltage feeder A selective leak detection protection device is installed on the upper part; a leak detection protection device with leakage lockout or a selective leak detection protection device is installed on the underground low-voltage feeder, and if there is no such two devices, an automatic cut-off leakage feeder must be installed. Leak detection device; selective leak detection protection device must be used together. It is not allowed to use the total leak detection device with delay; avoid immersing cables and electrical equipment in water, preventing squeezing and stabbing and causing cable damage; No burrs; no additional components; compensation for the ground capacitance of the grid.
3 Conclusion
In addition to the above measures taken, we should strengthen the management and repair of underground electrical equipment, electrical equipment regularly inspected and tested, to be replaced mainly the performance of funds under the conditions permit, modified or updated with Electrical equipment that is in operation or overdue, and various types of safety protection devices that cannot be reliably operated; properly equipped with necessary testing instruments, instruments, maintenance, repair tools and spare parts to ensure the normal operation of electrical equipment, and at the same time strengthen basic management and establish We will improve the rules and regulations for the installation, commissioning, use, maintenance, overhaul and accountability of all kinds of electrical equipment, and strictly implement and implement them; improve all kinds of safety protection devices for underground electrical equipment, and increase daily routine in strict accordance with regulations and systems. Inspect and patrol inspections to prevent malfunctions or inactions; strengthen education, raise awareness of the importance of the safety and protection of underground electrical equipment by cadres and workers, understand the correct use of electrical equipment and various protective measures, and put an end to practical work. In order to catch up with production, catch up with progress, and get rid of the protection device; Do a good job in technical training for the procurement, testing, installation, commissioning, maintenance, maintenance and other personnel of electrical equipment, and institutionalize and regularize the training, conscientiously fulfill the post responsibility system, and comprehensively improve the technical quality and business level of all types of personnel. This is the basis for ensuring safe production, and it is also the requirement for safe production of enterprises.
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