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Fire hazard of wire and cable laying and preventive measures
Mar 30, 2018

Fire hazard in laying of electric power system wires and cables In the process of cable manufacturing, the electrical insulation performance of cable body decreases, the insulation is destroyed, and the hidden danger of fire is buried.


The main reasons are as follows: The insulating medium contains impurities, moisture and air bubbles, the thickness of insulating layer is uneven, the main insulation and the conductor and shielding layer between the surface roughness, burr, gas gap, resulting in uneven distribution of electric field intensity in the insulating layer. Cable and thermal pipeline distance too close or cable long-term overload, the temperature too high insulation materials aging, overheating caused short-circuit spontaneous combustion, resulting in decreased insulation performance, puncture ignition.


Cable Bridge on the cable tray due to thermal expansion and contraction of the tension and the edge of the cable bridge to the mechanical damage to the cable, damaged the cable's protective layer and insulating layer, so that the electrical insulation performance decreased. Cable Head and terminal box fault spontaneous combustion, because the production process is rough, the stripping of the insulation in the air exposure time is too long, so that the insulator damp, resulting in the operation of the explosion.


The surface of the cable head is damp or accumulates dirt, the cable head porcelain casing is broken and the lead line is too small and so on. Cable middle joint is not tight, welding is not strong, the operation occurs oxidation; The insulating material dose of the middle junction box of the injection cable does not meet the requirement, or there is a hole in the box;


Bad sealing of the cable box or damaged crack immersed in moisture, so that insulation breakdown, fire explosion.


Cable tunnel stacking debris, cable or cable support is too thick, cable tunnels have flammable gas flammable liquid leakage, such as through high temperature or open flame ignition, the cable fire or explosion. The dielectric coefficient and volume resistivity of the widely used winding insulating material are lower than that of the cable body, such as dielectric coefficient and volume resistivity. Under the action of strong electric field, the internal dielectric loss of insulating material and the increase of leakage current will cause heating of cable accessory.


Plus the cable terminal head and the middle connector Conductor connection, is the on-site use of crimping manual crimping, the contact resistance of the pressure is generally greater than the cable conductor core resistance, it is difficult to do with the cable conductor wire core resistance, which will also give cable, cable fire accident buried hidden dangers.


When the oil-immersed cable is laid, the high and low bit difference occurs, and the oil or cable head is infiltrated, which leads to the loss of insulating oil at the top of the cable end, and the thermal resistance increases the insulation coking and breakdown the fire. Human factors are another important cause of electric wire and cable fire accidents.


For example, operators do not regulate the operation according to the regulations, misoperation caused by the cable, cable short-circuit, the overload, aggravating the wire, the surface of the cable doubled heat, causing electrical fire accident.


Fire hazard and cause analysis in power system wire and cable laying In high-rise buildings, as wires and cables are laid in bundles to set up online racks, once the wires and cables have a fire, the consequences are disastrous. Because wires, cables are used in insulating layer are flammable rubber, polyvinyl chloride and other hydrogen polymer organic compounds, in the burning of the heat generated up to 19000~46000kj/kg. Wire, cable copper core melting point of about 1038 ℃, aluminum core melting point in 658 ℃, and wire, cable insulation layer of the melting point is far below these values, such as PVC melting point of only 120 ℃. When the group of wire and cable accidents occur hot melt temperature reaches 800~1100℃, the threat to high-rise buildings is particularly great, the smoke in the accident, it is difficult to observe the fire source, the accident treatment is very difficult.


In recent years, the tragedy of the Sichuan department store and the Kowloon Building in Hong Kong was caused by wires and cables. An electrical fire accident can cause other chain accidents. Generally speaking, plastic wire, cable not only burning spread fast, but also produce a large number of toxic and harmful gases, such as hydrogen chloride, carbon monoxide and so on, so that people in a state of suffocation, poisoning, facing the danger of death.


At the same time, when the halide gas combustion reaction will generate a strong acid mist, making "two pollution", so that modern intelligent high-rise electrical and electronic equipment by acid erosion, the consequences are quite serious.


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