Fire protection measures for wires and cables are important (1)
Power cables have flammability and stringency due to long-term conductive heat. In the event of a fire, the hazard is serious, especially in power plants and large substations. Once a fire occurs, it will affect other circuits. Therefore, the fire protection technology of
power cables is one of the important technologies for the normal operation of electrical systems.
Power cables are an important part of electrical engineering and are used to transmit and distribute electrical energy. The power cable is composed of an insulated core
electrice wire, an insulating sheath and a protective layer. In order to adapt to various complicated laying environments, the
power cable is designed to have good insulation performance, waterproof performance and mechanical properties. However, when an overcurrent occurs in the cable loop and the cable overheats, the performance of the cable changes, which in turn causes a fire. This paper intends to discuss the fire protection technology of cables.
1. Create a good operating environment to avoid accelerated aging and damage of cable insulation.
Cable trenches and cable tunnels should have good drainage facilities, such as water shallow trenches and water collecting wells, and can effectively drain water. If necessary, set up automatic water pumping and stop pumping devices to prevent water supply and keep the interior dry. The cable trench and the longitudinal direction of the tunnel maintain the drainage slope. Prevent water, corrosive gases or liquids, and flammable liquids or gases from entering cable trenches and cable tunnels. The cable tunnel should be naturally ventilated. When the normal load of the cable is used to make the air temperature in the tunnel higher than 40~50 °C, the natural exhaust and mechanical exhaust can be combined to ventilate. The fan of the ventilation system should be interlocked with the fire detector to ensure automatic wind stop when the tunnel fires. The cable tunnel should not be used as the air inlet of the ventilation system.
The cable fire door should be avoided in the normally closed state, the cable should be completely enclosed by the fire barrier, and the gap of the cable trench cover should be filled and closed to affect the ventilation and heat dissipation of the cable. Moreover, the cable is completely enclosed, which makes the normal inspection of the cable impossible, and the cable failure cannot be found in time.
According to statistics, cable fires and explosions caused by cable head failures account for about 70% of the total cable accidents. Material and process quality must be produced in strict air cable heads. It is required that the service life of the cable head produced cannot be lower than the service life of the cable. The rated voltage level and insulation level of the street shall not be lower than the rated voltage level of the connected cable and its insulation level. The withstand voltage between the insulating mats on both sides of the insulating head shall not be less than 2 times the insulation level of the cable protective layer. The form of the joint should be compatible with the environmental conditions set and will not affect the flow capacity of the cable. Within the range of 2 to 3 m on both sides of the cable head, fireproof tape should be used for fire retardant treatment.
Generally speaking, the cable sees the weak link of cable insulation, so strengthening the monitoring and management of the cable head is an important part of cable fire prevention. Terminal cable heads must not be placed in cable trenches, cable tunnels, cable trays, cable mezzanine intermediate cable heads must be registered, and use a variety of testing equipment for testing. When the cable head is found to have abnormal temperature rise or odor or smoke, the emergency will be withdrawn early to prevent the cable from being fired during operation.
A sufficient safe length distance should be ensured between the intermediate cable heads. Two or more cable heads should be placed in the same position, and strict sealing measures should be taken between the cable head and other cables.
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