This paper mainly expounds the technical issues of the principle, composition and requirements of the power supply system of the comprehensive working face, the general requirements of the electrical clearance and creepage distance, the protection level and other explosion-proof electrical equipment.
District; power supply system; explosion-proof electrical equipment 1.1 comprehensive working surface power supply system principle to reduce the number of switches, starters, one starter controls one motor; when the power distribution points are connected in parallel, the starter is not set The main feed switch for the incoming line; the mechanical operation of the fully mechanized mining face should be powered by a radiant separate cable; when the motor of the scraper conveyor is not too large, it should be powered by the mains cable. When the capacity is large, the radiation can be used. Single cable power supply; working area distribution point maximum capacity The starter of the motor should be close to the incoming line of the distribution point, reducing the cross section of the connecting cable between the starters. Reduce cable length and reduce re-powering. The selected cable bus section is not 70mm2. 1.2 The structure of the power supply system of the fully mechanized mining face is composed of high-voltage explosion-proof distribution box, high-voltage double-shielded flexible cable, high-voltage cable connector and mobile substation. The composition of the low-voltage 1140V system: the mobile substation reduces the 6kV to 1140V, and the low-voltage feed switch with leakage, over-current and short-circuit protection devices is connected to the vacuum magnetic starter via the shielded cable, and is fed to the electrical equipment through the shielded cable.
1.3 The power supply system of fully mechanized mining face requires more equipment for fully mechanized mining face, large capacity of electricity, wide mining area and fast recovery speed. The use of fixed substation cannot meet the requirements. The power supply mode of mobile substation should be adopted to shorten the low voltage. The length of the 1140V power supply cable reduces the voltage drop and improves the quality of the power supply.
2 In order to ensure the start-up and normal operation of the large-capacity coal-fired unit, it is required to increase the supply voltage of the mining area.
3 Electrical equipment should have good protection devices, set overload, short circuit, under voltage, leakage lock, leakage protection, etc., and current, voltage, fault and other indicating devices, if there is an electrical accident, immediately cut off the power.
4Use high-protection shielded cable and double-shielded cable; the power distribution point should be equipped with starter and switch to facilitate replacement of the switch after damage; the control circuit of vacuum magnetic starter adopts safety spark circuit.
2 General requirements for explosion-proof electrical equipment Mine explosion-proof electrical equipment is an explosion-proof electrical equipment specially produced for use in coal mines in accordance with national standards. The categories of explosion-proof electrical equipment are specified, among which are coal mine underground electrical equipment.
2.1 Clearance and creepage distance Clearance and creepage distance are different concepts that are both different and related. The clearance is the shortest distance between two bare conductors, that is, the shortest clearance between the metal conductors with potential differences in electrical equipment usually includes: the shortest between live parts and between live parts and grounded parts. Air distance; the shortest air distance between live parts and accessible parts.
The requirements of the clearance are met, and the breakdown discharge is not between the bare conductors and between them to ensure the safe operation of the electrical equipment. Creepage distance is the shortest distance between two conductors along the surface of their solid insulating material. That is, the shortest distance along the insulating surface between adjacent metal parts with potential differences in electrical equipment. The creepage distance is determined by factors such as the rated voltage of the electrical equipment, the resistance to leakage of the insulating material, and the surface shape of the insulating material. The higher the rated voltage, the greater the creepage distance; otherwise, the smaller.
Electrical equipment must have a sturdy outer casing, which has certain protective capabilities and meets certain protection level standards. The degree of protection is anti-foreign and waterproof. It is to avoid the external solids entering the inside of the device and to avoid the human body touching the charged or moving parts of the device. Protection against external moisture entering the equipment and harmful effects on the equipment.
―General requirements for different types of explosion-proof electrical equipment have different characteristics, to make special provisions for them. For explosion-proof electrical equipment, they have common characteristics, which is a general requirement for explosion-proof electrical equipment. Regardless of the type of electrical equipment, the explosion-proof performance is guaranteed under the conditions of general requirements and special regulations.
1 If the explosion-proof electrical equipment adopts plastic casing, it should be made of non-combustible material, and ensure that the insulation resistance of the plastic surface is not more than 1000, avoid accumulating static electricity, withstand impact test and thermal stability test; the explosion-proof electrical equipment is limited to use aluminum alloy casing to avoid It rubs against rust iron to generate a lot of heat and prevents the formation of dangerous temperatures.
2 Fasteners are the main components of explosion-proof electrical equipment. A typical fastener consists of a bolt and nut and a spring pad for anti-loose. Special fasteners should be used for explosion-proof electrical equipment that uses special fasteners. For example, the connection of each part of the explosion-proof electrical equipment housing should be protected by a retaining ring type fastener to avoid accidental opening of the outer casing and loss of explosion-proof performance. Use retainer type fasteners to meet the following requirements: the bolt head or nut should be placed in the retainer, only use special tools to open; the upper surface of the bolt head or nut after tightening should not exceed the retainer; the retainer can be set Opening; the retaining ring should be firmly connected to the main body. All kinds of fasteners should be made of stainless material or rust-proof.
3 In order to avoid accidents caused by misoperation of electrical equipment, explosion-proof electrical equipment should be equipped with interlocking devices. When the device is powered, when the detachable part is disassembled, the device cannot be powered to ensure safety. The insulating sleeve fixed to the outer casing of the equipment for passing the wires through the partition is made of an insulating material that is not hygroscopic, and the use of the insulating sleeve does not change the explosion-proof form of the electrical equipment. If an insulating sleeve or electrical device requires the use of a binder, it must be resistant to mechanical, thermal and chemical properties.
4 In order to ensure the electrical equipment wires and cables are firmly connected, avoid sparks, arcs, and tender explosions in the operation of electrical equipment. For electrical equipment with spark, arc or dangerous temperature, the power is greater than 250W or the current is greater than SA. Junction boxes and connectors are used for electrical equipment, cable and wire connections. The form of the junction box is determined according to the use environment and related technical requirements. The space of the wire bending radius should be left in the junction box; the clearance and creepage distance between the exposed conductors in the box should meet the requirements of explosion-proof type; to avoid arcing and flashover, the inner wall of the junction box should be coated with arc-proof paint.
5 connectors are for cable or wire wiring. The connecting piece should have sufficient mechanical strength and structural size to ensure reliable wire connection, to ensure that the connection is not loose under the influence of vibration and temperature, and there is no spark, overheating and poor contact. A copper-aluminum transition joint is applied to the connection to the aluminum core cable.
6 The introduction device is a transition device for the cable or wire of the circuit outside the explosion-proof electrical device to enter the device, and the sealing of the introduction device is very important. The introduction method is widely applied, and includes a pressure plate type introduction device and a compression nut type introduction device. The material of the sealing ring used for the introduction device is made of a rubber material or the like which is elastic, not easy to be aged, cracked, or the like. The sealing ring only has the hardness to be suitable for sealing and anti-loosening, and to ensure the explosion-proof performance. The introduction device should have a lock-proof and pull-out prevention device.
7 In order to avoid the explosion of the surrounding flammable gas mixture caused by personal electric shock or ground discharge when the electrical equipment casing is energized, the explosion-proof electrical equipment must be well grounded. It mainly includes the grounding terminal of the metal casing of the equipment and the internal grounding terminal in the equipment junction box. The inner ground h terminal must be marked with the grounding symbol "earth" grounding parts made of stainless steel or rust-proof. Whether it is the inner ground terminal or the oh h grounding terminal, the selection specifications must match the electrical equipment capacity. The larger the power of the device, the larger the diameter of the terminal. The portable or moving electrical equipment needs to be moved without the grounding device. The cable with the grounding core is connected to the grounding core and connected to the underground grounding grid. .
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