Fire prevention and explosion-proof measures and m

2022-09-21
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Fire prevention and explosion-proof measures and methods for electrical equipment

electrical fire and explosion electronic universal experimental machine is a new generation of double space electronic universal experimental machine specially described for colleges and universities and scientific research institutes. Explosion accident refers to fire and explosion accidents caused by electrical reasons. Most of the insulating materials of various electrical equipment are flammable substances. During operation, the conductor will heat up through the current, and the switch will produce an arc when cutting off the current. Due to short circuit, grounding or equipment damage, arcs and sparks may be generated, which will ignite the surrounding inflammables and cause fire or explosion accidents. Baiyongxiao, a professor of fire and Lanzhou University, said that the explosion accidents accounted for a large proportion. In addition to personal injury and equipment damage, electrical fire and explosion accidents may also cause large-scale or long-term power failure of the system, causing heavy losses to the national economy. Therefore, electrical fire and explosion prevention is an important part of safety management

ignition refers to the phenomenon that the local part of the combustible is affected by the high-temperature heat source, which causes the combustible to burn and gradually expand to the whole. Usually, most fires are caused by ignition. Sometimes, fire and explosion happen together. Explosion refers to the phenomenon that substances undergo violent oxidation and decomposition reactions, resulting in a sharp increase in temperature and pressure. Explosion is also a special burning phenomenon

combustible gas, liquid and dust are mixed with air and explode when encountering open fire and heat source. The lowest concentration of its mixture is called the lower explosive limit, while the highest concentration is called the upper limit, which is usually expressed in volume percentage

1 causes of electrical fire and explosion

electrical fire and explosion, in addition to the design, manufacturing and construction reasons such as equipment defects or improper installation, there are also direct reasons such as heat and electric sparks or arcs generated in operation

1.1 overheating of electrical equipment

overheating of electrical equipment is mainly caused by the thermal effect of current. When the current passes through the conductor, due to the resistance of the conductor, a certain amount of electric energy will be consumed when the current passes through. This energy is consumed in the form of heat and heats other materials around it. When the temperature exceeds the allowable temperature of electrical equipment and its surrounding materials, it may cause a fire when it reaches the ignition temperature

electrical equipment overheating is mainly caused by the following reasons:

1) short circuit: when a short circuit occurs in the line, the current in the line will increase to several times or even dozens of times the normal working current, causing the equipment temperature to rise sharply, especially at the contact resistance of the connecting part. If the temperature reaches the ignition point of combustibles, it will cause combustion

there are many reasons for line short circuit, such as insulation damage of current carrying part of electrical equipment. This damage may be caused by long-term operation, natural aging of insulation, or the strength does not meet the requirements, or the insulation is damaged by external forces, which may cause short circuit accidents, or the arc short circuit caused by misoperation during operation. There are also short circuits caused by small animals entering the charged Bay by mistake, and birds crossing the exposed phase lines. In case of short circuit, the fault part shall be cut off at the fastest speed to ensure the safety of the line

2) overload: heating will be caused by unreasonable conductor section and equipment selection, or the current in operation exceeds the rated value of the equipment, exceeds the optimized industrialization of new materials and the long-term allowable temperature of the utilization environment

3) poor contact: the wire connector is not firmly connected, and the movable contact (switch, fuse, contactor, socket, bulb and lamp holder, etc.) is in poor contact, resulting in a large contact resistance, and the current flow leads to overheating of the connector

4) iron core overheating: the iron core of transformers, motors and other equipment is over saturated, or high-order harmonics caused by nonlinear loads cause iron core overheating

5) poor heat dissipation: the heat dissipation and ventilation measures of the equipment are damaged, and the heat generated during the operation of the equipment cannot be dissipated in time and effectively, resulting in overheating of the equipment. Improper installation or use of some electrical equipment with high calorific value may also cause fire

1.2 arc and spark

arc and spark are a common phenomenon. For example, electric arcs and sparks may also occur during normal operation or normal operation of electrical equipment. During normal operation, there will be electric sparks at the sliding contact between DC motor brush and commutator, and at the sliding contact between AC motor brush and slip ring. When the switch disconnects the circuit, a strong arc will be generated. When the plug is unplugged or the contactor disconnects the circuit, there will be electric sparks. The arc generated in case of short circuit or grounding accident is larger. There will be electric sparks and arcs when the insulation is poor. The temperature of electric spark and arc is very high, especially the temperature of arc can be as high as 6000 ℃. Such a high temperature can not only cause combustibles to burn, but also melt and splash metals, forming a dangerous fire source. In places with explosion hazards, electric sparks and arcs are even more dangerous factors

electrical equipment itself will also explode, such as transformers, oil circuit breakers, power capacitors, voltage transformers and other oil filled equipment. The space around electrical equipment will cause explosion under the following conditions:

1) there is explosive mixture in the surrounding space, which may cause space explosion when encountering electric sparks and arcs

2) the insulating oil of oil filled equipment decomposes and vaporizes under the action of electric arc, ejects a large amount of oil mist and combustible gas, and may also cause fire and explosion accidents when encountering electric sparks, electric arcs or when the ambient temperature reaches a dangerous temperature

3) if hydrogen leaks from hydrogen cooled generators and other equipment, forming explosive mixtures, explosion and fire accidents will also be caused when electric sparks, arcs or ambient temperatures reach dangerous temperatures

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