Research on Safe Operation Technology of Mine Electrical Equipment in Power and Electrical Engineering 1 Han Chuanmao (Anhui Institute of Safety Production Science and Technology) Hefei plays a very important role in avoiding and reducing the occurrence of major underground safety incidents. This paper discusses the basic techniques for safe operation of mine electrical equipment.
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1: Han Chuanmao (1984-), male (Han nationality), Native Place: Huoqiu, Anhui Province, Helper, undergraduate, Direction: Mine Electrical Safety, Unit: Anhui Institute of Safety Production Science.
1 Importance of safe operation of mine electrical equipment Safety requirements for mine power supply and distribution The electrical energy required by mines generally comes from the power grid, passes through the power transmission lines to the mine substation, and is sent to each power consumption location after the transformer is stepped down. The transformers, power distribution units, power lines and various electrical equipment of the transformer substations at each level of the mine are connected to each other in a certain way to form the power supply system of the mine. Due to the particularity of the mining production environment, it requires reliable power supply, safety, high quality, and economy. For major load of mining enterprises, such as main drainage, ventilation and lifting equipment, once the power supply is interrupted, accidents such as inundation of mines, accumulation of toxic and hazardous gases, or suspension of tanks or even drop of tanks may occur. Power interruptions such as mining, transportation, air pressure, and lighting can also cause varying degrees of economic loss or personal accidents. Mine mining can not be separated from electrical equipment, and the safety of electrical equipment operation is related to the entire mining. Therefore, it is of great significance to strengthen the safe operation of mine electrical equipment.
2 Safety protection technology for electrical equipment 2.1 Neutral point grounding method What kind of grounding method is adopted for the power transformer neutral point of the power supply system, and the choice of the electrical protection scheme is extremely related to the safe operation of the power grid. Low-voltage power supply system generally has two power supply methods. One is to connect the neutral point of the distribution transformer to the ground through a metal grounding body, and the neutral point is directly grounded; the other is the neutral point and ground insulation. Neutral point is not grounded. Both of these grounding methods are short and long, suitable for different places of use, and must have corresponding electrical protection devices to ensure the safe operation of the power grid.
Due to the poor underground mine environment, the requirement for safe electricity is particularly high. For this reason, the safety regulations for metal non-metallic mines stipulate that underground power distribution transformers and the stope of metal open pit mines must not use a neutral point directly grounded power supply system; The power supply system for the low-voltage electrical equipment on the ground outside the system and on the surface of the open pit stope is generally a system that is directly earthed at the neutral point. In order to avoid and reduce the danger of high pressure depressing the low voltage, it is necessary to reliably connect the neutral point with the ground through the breakdown fuse, or install a lightning arrester on the three-phase line.
2.2 Earthing and Zeroing Electrical equipment in operation may cause dangerous earth-to-ground voltages on its metal enclosure and on other metal objects in contact with electrical equipment due to insulation damage. After contact with the human body, there is a risk of electric shock. In order to avoid electric shock accidents, the most commonly used protective measures are grounding and zeroing.
In the 220V neutral three-phase four-wire neutral power supply system, the normal uncharged case of the device is connected to the neutral point grounded zero line, which is called protection zero. When the charged part of a certain phase collides with the shell of the metal device, a single-phase short circuit of the phase line to the neutral line is formed through the shell of the device, and the short-circuit current can make the over-current protection device (such as a fuse ruler) on the line act quickly. This will cut off the power supply and eliminate the risk of electric shock.
2.3 Relay protection When the power system fails or shows abnormality, in order to remove the fault part, or to prevent the fault area from expanding, to reduce the fault loss and ensure the safe operation of the system, some electrical automatic devices need to be used for protection. The main components of the automatic device are Relays, protective devices equipped with relays are called relay protection devices.
2.4 Leakage Protection When a circuit or electrical device is defective, causing live parts to come into contact with the ground, causing bodily harm, damage to the equipment, or risk of fire, the protection of the power supply may be called leakage protection. Leakage protection devices are mainly voltage type and current type. The leakage protection device of underground low-voltage power grids is generally equipped with a leakage relay at the power supply end to monitor the insulation of the power grid. When the grid insulation is lowered (leakage) to a certain value or grounded, the leakage relay will act and switch off the main power switch automatically in a very short time. When the human body gets an electric shock, the leakage relay will also act. 2.5 Overcurrent Protection Overcurrent means that the current of the electrical equipment or line exceeds the specified value, and there are two cases of short circuit and overload. Short circuit and overload will cause the electrical equipment or circuit to heat beyond the allowable limit, causing insulation damage, equipment or lines burned, and even cause a fire accident. In order to ensure safe and reliable power supply, over-current protection devices should be installed in the power grid or electrical equipment. When a short-circuit or overload fault occurs in the power grid, the over-current protection device acts to quickly and reliably remove the fault and avoid serious consequences. Commonly used over-current protection devices are fuses, thermal relays, electromagnetic over-current relays 2.6 lightning protection Lei is a phenomenon of discharge in the atmosphere. This kind of discharge has very short time, great current, up to 200kA300kA, discharge temperature up to 20000C, instantaneous flash of shining sparks and deafening roar, powerful destructive power, which can instantly kill people and livestock, burn houses and In other buildings, the insulation of electrical equipment was destroyed, resulting in a large-scale, long-time blackout, and even a fire and explosion. The damage was very serious. Lightning protection includes the lightning protection of power systems and the lightning protection of buildings and other facilities. The main measures are the use of lightning rods (wires, nets) and lightning arresters.
Lightning rods, lightning conductors and lightning protection nets can protect buildings, buildings and high-voltage transmission lines from lightning strikes. Chimneys, water towers, derricks and tall buildings, as well as houses containing flammable and explosive substances (such as explosive magazines, oil depots, etc.) should be equipped with lightning rods (wires, nets). Arrester is an overvoltage protection device used to limit the overvoltage amplitude of the power system to protect electrical equipment.
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