Electrical equipment fire and explosion-proof safety technology
In order to ensure production safety and the use of electrical equipment, to prevent electrical equipment due to improper installation and use of fire and explosion accidents should be based on the use of electrical equipment environment, respectively, to take the following corresponding safety technology measures. Below I share with you electrical equipment fire and explosion safety technology, ha UN should be read and browsed.
1) the division of hazardous environments
In order to correctly select the electrical equipment, electrical circuits and a variety of explosion-proof facilities, it is necessary to correctly classify the size and level of the hazardous areas of the environment.
(1) gas, vapor explosion hazardous environment.
According to the frequency and duration of explosive gas mixtures, the hazardous environment can be divided into 0, 1 and 2 areas.
Ventilation is an important factor in the division of explosive hazardous areas. Division of hazardous areas, should take into account the release source and ventilation conditions, and should follow the following principles:
① for natural ventilation and general mechanical ventilation of the premises, continuous level release source can generally lead to the formation of the surrounding 0 area, the first release source can lead to the formation of the surrounding 0 area, the second release source can lead to the formation of the surrounding area of 1 area (including local ventilation), such as the absence of ventilation, the regional hazard level should be increased, the first level of release source may lead to the formation of Zone 1, the second level release source may lead to the formation of Zone 2. However, good ventilation may result in a reduced or negligible extent of the explosion hazardous area, or it may result in a lower rating or even classification as a non-explosion hazardous area. Therefore, the release source should try to use open-air, open arrangement to achieve good natural ventilation, in order to reduce the risk and save investment. On the contrary, if the ventilation is poor or ventilation direction is not appropriate, can make the scope of the explosion hazardous area to expand, or make the hazardous level higher. Even in the case of only one level of release source, different ventilation may be the release source around the range into different levels of the area.
② local ventilation in some occasions to dilute explosive gas mixtures than natural ventilation and general mechanical ventilation is more effective, and thus can make the explosion hazardous area of the regional scope of narrowing (sometimes as small as negligible), or make the level of reduction, or even divided into non-explosive hazardous areas.
③ release source in the unventilated environment, may increase the level of the explosion hazardous area, continuous level or the first level of the release source may lead to zone 0, the second level of the release source may lead to zone 1.
④ in the obstacles, pits, dead ends, etc., due to poor ventilation, localized areas to increase the level and scope. On the other hand, obstacles such as embankments or walls may sometimes reduce the explosion hazard range by limiting the spread of the explosive mixture (the density of the gas or vapor should also be taken into account).
(2) dust, fiber explosion hazardous environment.
Dust, fiber explosion hazardous area refers to the production of equipment in the environment around the suspended dust, fiber amount is enough to cause an explosion, as well as in the surface of the electrical equipment will form a layer of dust, fiber and may cause spontaneous combustion or explosion of the environment. In GB 4208?1984 standard, according to the frequency and duration of explosive gas mixtures, such hazardous environments are divided into 10 and 11 areas.
Classification of dust, fiber explosion hazardous environment, should take into account the size of the dust, the explosion limit of the high and low and ventilation conditions. For good airflow open or partially open buildings or open-air installations, after taking into account the specifics of the explosion limit and other factors, can be divided into a lower level of hazardous areas. If equipped with sufficient dust removal effect of dust removal devices, and when the dust removal device stops running, explosive dust environment in the process unit can be chained to stop, can also be divided into a lower level of hazardous areas.
The exhaust fan room for the dust explosion hazardous environment services, should be the same as the exhaust environment of the hazardous level.
Dividing the hazardous area of suspended dust, should be considered in the environment of suspended dust formation conditions, granularity, dust concentration, treatment, dust leakage from the equipment or pipeline to the outside, the size of the leakage, as well as the amount of dust, the size of the workspace, the presence of effective air exchange devices, mechanical device failure and its potential to cause dust suspension, the configuration of the mechanical device, the isolation situation and operating conditions. The configuration, isolation and operating conditions of the mechanical devices.
Delineation of the hazardous area of cascading dust, should take into account the possibility of spontaneous combustion and the size of the dust fall accumulation per unit of time, the shape and configuration of the mechanical device, there is no dust flying, whether the ventilation is good, the number of times and the difficulty of cleaning cleaning, etc.. Special attention should be paid to the formation of layers of dust on the heating surface, if the thickness of the accumulation layer is large, at lower temperatures will also be spontaneous combustion or even explosion.
Delineation of hazardous areas adjacent to the plant, should be based on the specific circumstances of the dust or fiber diffusion and deposition of the delineation of its hazardous level and scope.
For non-open hazardous environments, the production plant should be divided into hazardous areas. For open and semi-open environment, plant boundaries within the 10 zone, the open surface outside the horizontal distance of 7.5m (15m when poor ventilation), the ground and the roof above the 3m space should be classified as 11; plant boundaries within the 11 zone, the open surface outside the horizontal distance of 3m, the ground above the 3m, above the roof of the space above the 1m should be classified as 11 zone.
For centralized open-air devices, the device group should be outside the contour line of the horizontal distance of 3m, the vertical distance of 3m of space as the boundaries of zoning or 11 boundaries; such as within the 10 zone, then outside the horizontal distance of 15m, the vertical distance of 3m of space is designated as the 11 zone.
(3) fire hazardous environment.
The fire hazardous environment is divided into 21, 22 and 23 zones, and the old standard H?1, H?2 and H?3 fire hazardous places one-to-one correspondence, respectively, there are combustible liquids, combustible dust or fibers, combustible solids exist in the fire hazardous environment.
2) Selection of electrical equipment in explosion-hazardous environments
Selection of electrical equipment should be mastered before the explosion-hazardous environment of the relevant information, including the environmental level and regional scope of the division, as well as in the environment of the level of explosive mixtures, groups, and other relevant information.
Electrical equipment should be used according to the level of the environment, the type of electrical equipment and the use of conditions for the selection of electrical equipment.
The level and group of the selected explosion-proof electrical equipment should not be lower than the level and group of explosive mixtures in the environment. When there are more than two explosive substances, should be mixed according to the level of explosive mixture and group selection. If there is no evidence and impossible to test, according to the higher level of risk and group selection.
Explosion-hazardous environments within the electrical equipment must be in line with current national standards and national inspection department explosion-proof certificate of conformity of the product.
Electrical equipment in explosion-endangered environments should be able to prevent the surrounding chemical, mechanical, thermal and biological factors of harm, should be compatible with the ambient temperature, air humidity, altitude, solar radiation, wind and sand, earthquakes and other environmental conditions. Its structure should meet the requirements of electrical equipment in the specified operating conditions will not reduce the explosion-proof performance.
The maximum surface temperature of explosion-proof electrical equipment for mining, no coal dust deposits shall not exceed 450 ℃, coal dust deposits shall not exceed 150 ℃. Dust, fiber explosion hazardous environment, the maximum surface temperature of general electrical equipment shall not exceed 125 ℃, if the deposition thickness of 5mm or less below 75 ℃ below the ignition temperature, or not more than 2/3 of the ignition temperature.
In explosion hazardous environments, should be used as little as possible with portable equipment and mobile equipment, should be installed as little as possible plug seat.
In order to save money, should try to reduce the use of explosion-proof electrical equipment. First of all, should consider installing hazardous equipment outside the hazardous environment; if you have to install in the hazardous environment, should also be installed in a less dangerous location.
The use of non-explosion-proof equipment bulkhead mechanical transmission, the bulkhead must be non-combustible materials of the solid wall, through the shaft holes should be blocked, the installation of electrical equipment in the room of the exit can only lead to non-explosive hazardous environments; Otherwise, it must be maintained at a positive pressure.
3) explosion-proof electrical wiring
In the explosion-hazardous environment, the electrical wiring installation location, laying methods, conductor materials, connection methods, etc. should be based on the environment of the hazardous level of choice.
(1) gas, vapor explosion hazardous environment of the electrical line.
① Selection of the location of the electrical line.
In the explosion hazard is smaller or farther away from the location of the release source, should consider laying electrical lines. For example, when the explosion hazardous gases or vapors heavier than air, the electrical line should be laid at a high place, the cable is directly buried or cable trench sand-filled laying; when the explosion hazardous gases or vapors lighter than the air, the electrical line is suitable for laying in the low place, the cable is to take the cable trench laying.
Electrical lines should be laid along the external walls of the building with an explosion hazard. When the electrical line is laid along the pipeline stacks conveying flammable gases or flammable liquids, should try to lay along the side of the pipeline with a lower degree of risk. When flammable gases or vapors heavier than air, the electrical line should be above the pipe; when flammable gases or vapors lighter than air, the electrical line should be below the pipe.
Electrical lines should be avoided may be subject to mechanical damage, vibration, pollution, corrosion and heat; otherwise, protective measures should be taken.
10kV and the following overhead lines shall not cross the explosion-hazardous environment; when the overhead lines and explosion-hazardous environments adjacent to the distance between them shall not be less than 1.5 times the height of the tower.
② line laying method of choice.
Explosion-hazardous environments, electrical lines are mainly explosion-proof steel wiring and cable wiring, the laying method should meet the requirements. Explosion-hazardous environments shall not be open electrical lines.
Fixed laying of power cables should be armored cable. Fixed laying of lighting, communication, signaling and control cables can be armored cable and plastic sheathed cable. Non-fixed laying of the cable should be used non-plastic rubber sheathed cable. Coal mine underground high-voltage cables should be armored non-drip type cable.
Cables for different purposes should be laid separately. Steel pipe wiring should use special galvanized steel pipe or the use of water pipes or gas pipes that have been treated with inner wall burrs and anti-corrosion treatment of the inner and outer walls.
Between two sections of steel pipe, steel pipe and steel pipe accessories, steel pipe and electrical equipment should be threaded connection, thread engagement of not less than 6 buckles, and should take anti-loosening and anti-corrosion measures.
Steel pipe and electrical equipment directly connected to the difficulties, as well as pipelines through the building expansion joints, settlement joints should be installed flexible connecting pipe.
③ Isolation seal.
The laying of electrical lines in the trench as well as the protection of pipes, cables or steel tubes in the explosion hazardous environment through the different levels of the region between the partition wall or floor, should be non-combustible materials tightly plugged.
The location of the isolation sealing box should be as close as possible to the partition wall. No pipe joints, junction boxes or any other connections are allowed between the wall and the isolation sealing box.
The explosion-proof rating of the isolation sealing box should be compatible with the rating of the explosion-hazardous environment. The isolation sealing box should not be used as a connection or separation of wires. In places where condensation may be caused, drainage type isolation sealing box should be used. Steel pipe wiring isolation sealing box should be used powder sealing filler.
Between the protection pipe opening and cable of cable wiring, sealing mud should be used for sealing. The cable trench at the junction of the two-level area should be sand-filled, filled with fire-resistant materials or add a fireproof partition wall.
④ Conductor material selection.
Due to the low mechanical strength of aluminum-core wire, easy to break, the need for transition connection and increase the size of the junction box, and connection technology is difficult to ensure, so the aluminum-core wire and aluminum-core wires or cables have poor safety performance. If there are conditions, explosion-hazardous environments should be given priority to the use of copper wire.
Explosion-hazardous environment hazardous level 2 area within the scope of the power distribution lines, when the wire connection and cable sealing end using crimping, welding or brazing, power lines also take the cross-sectional area of 4mm2 and above the aluminum-core wire or cable, lighting lines can be used to cross-sectional area of 2.5mm2 and above the aluminum-core wire or cable.
Explosion-hazardous environment hazard class 1 zone ` within the scope of the power distribution lines should be selected with copper-core wire or cable.
Multi-stranded copper-core flexible wire or multi-stranded copper-core cable should be used in places with severe vibration. Aluminum core power cables shall not be used in coal mines.
Explosion hazardous environments within the wiring, generally cross-linked polyethylene, polyethylene, PVC or synthetic rubber insulation, wire or cable with a sheath. Explosion-hazardous environments should be used with heat-resistant, flame-retardant, corrosion-resistant insulation of wires or cables, should not be used oil-impregnated paper insulated cable.
In the explosion-hazardous environment, low-voltage power, lighting lines used in wires and cables shall not be lower than the rated voltage of the working voltage, the work of the zero line should be the same insulating capacity with the phase line, and should be in the same jacket.
Selection of electrical wiring should also be noted that: dry and dust-free places can be used in general insulated wire; wet, especially wet or dusty places should be used to protect insulated wires (such as lead-skinned wire) or general insulated wires through the pipe; high temperature places should be used with porcelain tubes, asbestos, porcelain beads and other heat-resistant insulation heat-resistant wire; corrosive gases or vapors can be used in places of lead-skinned wire or corrosion-resistant through the pipe. Pipe line.
⑤ Allowable current-carrying capacity.
In order to avoid possible dangerous temperatures, explosion-hazardous environments should not be higher than the permissible load capacity of non-explosion-hazardous environments. 1, 2 insulated wire cross-section and cable cross-section selection: the permissible load capacity of the conductor should not be less than the rated current of the fuse and the circuit breaker long-delay overcurrent detent rectification current 1.25 times; lead to the low-voltage caged induction motor branch line permissible load capacity should not be less than the rated current of the motor. The allowable load capacity of the branch line leading to the low-voltage cage induction motor should not be less than 1.25 times the rated current of the motor.
Line voltage 1000V or more wires and cables, should be calibrated according to the short-circuit current for thermal stability.
⑥ Connection of electrical lines.
Intermediate joints are not permitted for electrical lines in zones 1 and 2, but this is not the case if the connection of electrical lines is internal near a junction box or connector box of the type of protection appropriate to that hazardous environment. 1 zone is suitable for use of explosion-proof junction boxes, and 2 zones can be used to increase the safety of the type of junction box.
2 area of the electrical line if the choice of aluminum core cable or wire and copper connection, there must be a reliable transition joints with copper and aluminum. Connection or sealing of the conductor should be crimped, welded or brazed, and do not allow the use of simple mechanical binding or spiral winding of the connection.
(2) dust, fiber explosion hazardous environment electrical wiring.
Dust, fiber explosion-endangered environment, the technical requirements of electrical wiring and the corresponding level of gas, steam explosion-endangered environment, the technical requirements of electrical wiring is basically the same, that is, 10 areas, 11 areas of electrical wiring can be considered respectively according to the 1 area, 2 areas.
(3) fire hazardous environment electrical lines.
Fire hazardous environment of the electrical line should be avoided combustible materials. 10kV and the following overhead lines shall not cross the explosion hazardous environment, neighboring the distance between them shall not be less than 1.5 times the height of the tower.
When insulated wires are laid with pin or drum insulators, care should be taken to keep away from combustible materials, not in the unplastered wooden ceiling and wooden walls, etc., not in the wooden boring ceiling and combustible liquids pipeline stacks.
In the fire hazard environment, mobile and portable electrical equipment should be used mobile cable.
In the fire hazardous environment, bare aluminum, bare copper bus should be used, the following requirements should be met:
① do not need to disassemble the bus connection, should be used fusion welding or brazing.
② bolt connections (such as bus and electrical equipment connections) should be reliable, and should prevent automatic loosening.
③ In the 21st and 23rd districts, the busbar should be equipped with a metal mesh protective cover, and the diameter of its eyelets should be able to prevent solid foreign objects with a diameter greater than 12mm from entering the shell; in the 22nd district there should be a protective enclosure.
④ In the open air installation, there should be rain, snow measures.
Aluminum conductors can be used in fire hazardous environments. When using aluminum core insulated wire, there should be a reliable connection and sealing. Fire hazardous environment power, lighting lines and cables should not be less than the rated voltage of the network, and not less than 500V.
4) Electrical fire and explosion-proof basic measures
(1) Eliminate or reduce the explosive mixture.
Eliminate or reduce the explosive mixture is a general fire and explosion prevention measures. For example, to take closed operations to prevent leakage of explosive mixtures; clean up the site dust to prevent the accumulation of explosive mixtures; design of positive pressure chamber to prevent the intrusion of explosive mixtures; take open operations or ventilation measures to dilute explosive mixtures; fill the hazardous space with inert or inactive gases, to prevent the formation of explosive mixtures; the installation of alarm devices.
In an explosion-hazardous environment, such as good ventilation, can reduce the concentration of explosive mixtures, thereby reducing the hazardous level of the environment.
Batteries may have hydrogen discharge, there should be good ventilation. Transformer room generally use natural ventilation, if the use of mechanical ventilation, its air supply system should not be connected to the explosion-hazardous environment of the air supply system, and the supply of air should not contain explosive mixtures or other harmful substances. Several transformer room *** with a set of air supply system, each air supply branch should be installed on the fire damper, the exhaust system should be installed independently. Exhaust should not be located directly below the window.
The ventilation system should be made of non-combustible materials, the structure should be strong, the connection should be tight. There should be no dead space in the ventilation system to impede airflow. Electrical equipment should be interlocked with the ventilation system and must be ventilated before operation. The gas entering the electrical equipment and ventilation system should not contain explosive hazardous substances or other harmful substances. Exhaust gases discharged from the ventilation system should generally not be discharged into an explosion-hazardous environment. For closed-circuit ventilated explosion-proof ventilated electrical equipment and its ventilation system, clean gas should be supplied to replenish the leakage and maintain positive pressure in the system. Warning signs or interlocking devices should be provided on the doors or lids within the enclosure of the electrical equipment and its ventilation and filling system to prevent incorrect opening during operation. The control equipment of the motor for accidental venting in explosion hazardous environments should be located in a place that is easy to operate in case of an accident.
(2) Isolation and spacing.
Isolation is the installation of electrical equipment in separate rooms, and blocking measures on the partition wall to prevent the entry of explosive mixtures. Motor drive through the wall, should take appropriate sealing measures between the shaft and the shaft hole; the work of the spark-generating switchgear installed outside the scope of the hazardous environment (such as outside the wall); the use of outdoor lamps and lanterns through the glass window to the indoor lighting, etc., are all part of the isolation measures. Ordinary pull-wire switch immersed in insulating oil to run and make the oil level has a certain height, to keep the oil clean; ordinary fluorescent lamps into a high-strength glass tube and rubber plug tightly blocked at both ends, etc., are simple isolation measures.
Transformer, distribution room and explosion-hazardous environments or fire hazardous environments adjacent to the partition wall should be made of non-combustible materials. With the 1 zone and 10 zone environment *** with the partition wall, there should not be any pipe, ditch through; with the 2 zone or 11 zone environment *** with the partition wall, only allowed to pass through the pipe and ditch related to the variable, distribution room, holes, ditches should be non-combustible materials tightly plugged.
Doors and windows adjacent to the transformer and distribution room should open outward to an environment free of explosion or fire hazards.
Outdoor transformers, distribution stations and buildings, yards, storage tanks should maintain the required fire distance, and the larger the amount of transformer oil, the lower the fire resistance rating of the building and the larger the amount of storage of hazardous materials, the required distance is also larger, if necessary, can be added to the firewall. Open-air transformers, power distribution should not be set up in the easy deposition of combustible dust or combustible fibers.
In order to prevent electrical sparks or dangerous temperatures caused by fire, switches, plugs, fuses, electric heating appliances, lighting appliances, welding equipment and motors, etc., should be properly avoided according to the need to avoid combustible materials or combustible building components. Crane sliding contact line should not be stacked below the flammable items.
10kV and the following overhead lines, is strictly prohibited across the fire and explosion hazardous environment; when the line and fire and explosion hazardous environments close to the horizontal distance between the general should not be less than 1.5 times the height of the pole; in special circumstances, take effective measures to allow an appropriate reduction in distance.
(3) to eliminate the ignition source.
In order to prevent the emergence of electrical ignition sources, should be based on the characteristics of the explosion-hazardous environment and the level and grouping of hazardous materials selection of electrical equipment and electrical lines, and to maintain safe operation of electrical equipment and electrical lines. Safe operation includes current, voltage, temperature rise and temperature and other parameters do not exceed the permissible range, but also includes good insulation, good connection and contact, the whole intact, clean, clear signs and so on.
In explosion-hazardous environments, portable electrical equipment should be used as little as possible, with fewer plug holders and localized lights. In order to avoid sparks, in an explosion-hazardous environment to replace the light bulb should be de-energized operation. In the explosion hazardous environment should generally not be measured operation.
(4) explosion-endangered environment grounding and zeroing.
① Integral connection. In the explosion-hazardous environment, must be the metal parts of all equipment, metal piping and metal structure of the building all grounded (or zero) and connected into a continuous whole to maintain the current path is not interrupted. Grounding (or zero) trunk in the explosion-hazardous environment in different directions and not less than two places connected to the grounding body, the connection should be firm to improve reliability.
② protective conductor. Single-phase equipment should be separated from the protective zero line, phase line and zero line should be equipped with short-circuit protection elements, and install a double-pole switch to operate the phase line and the zero line. 1 and 10 areas of all electrical equipment, 2 areas in addition to lighting fixtures, other than the other electrical equipment should be used to special grounding (or zero) line, and metal pipelines, cables, such as metal cladding can only be used as an auxiliary grounding (or grounding). In addition to piping for conveying explosion-hazardous substances, lighting fixtures in Zone 2 and all electrical equipment in Zone 20 are allowed to utilize reliably connected metal piping or metal diffraction frames as grounding (or zeroing) wires.
③ Mode of protection. In the ungrounded distribution network, must be equipped with a phase of grounding or serious leakage can automatically cut off the power supply of the protective device or can issue a sound, light double signal alarm device. In the transformer neutral point directly grounded distribution network, in order to improve reliability and shorten the duration of short-circuit faults, the system single-phase short-circuit current should be larger.
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