Do you know cable fire hazards and protective measures?

In recent years, in the global power system fire accidents, the proportion of power supply interruptions due to power cable fires has been on the rise. Therefore, in power plants, substations and other places with a large number of electrical equipment and densely laid a large number of cables, it is increasingly important to use flame-retardant cables to prevent the spread of fire, and to use fire-resistant cables to ensure the uninterrupted power supply of important circuits. Therefore, it is very important to do a good job in the fire prevention and fire extinguishing of cables, so it is extremely important to fully and correctly understand the fire hazards and protective measures of cables.

First, the basic operation of cable fire protection

fire protection tape

In practical work, fire-resistant paint or fire-resistant tape is usually applied on both sides of power cable joints and adjacent 2-3m long cable segments, which can meet good fire protection requirements.

Fire retardant coating

It is mainly made of non-combustible inorganic materials and consists of organic binders, flame retardants, inorganic fillers, non-combustible fibers, etc. In case of fire, the fire retardant coating will expand and thicken to form a small and uniform honeycomb isolation layer, so as to play the role of flame retardant and fire prevention.

Plug the cable through the cavity

Organic flame retardant materials are composed of flame retardants, resins, fillers and the like. It has strong flexibility and can be cured and hardened at high temperature when the cable catches fire, preventing harmful gases, flames and thick smoke from burning along the cable line, so as to control the fire within a certain range; inorganic flame retardant materials are composed of flame retardants and It is composed of inorganic high temperature resistant materials, which has the characteristics of rapid condensation and no expansion when heated. They are more suitable for plugging into holes between panel cabinets, floors, and cable run-through walls. Compared with organic flame retardant materials, they are less expensive, but it is not easy to replace the cable after the plug is cured, so it is often used with organic flame retardant materials.

New Technology Application - Comb Firewall

Comb-shaped cable line firewalls can be used when retrofitting existing cables, and the comb teeth should correspond to the gaps in the cable layers. The cables are passed through perforations in the firewall, and the remaining gaps in the perforations can be filled with flame retardant material. This type of fire wall can be made of a comb-shaped wall made of ordinary steel plates, and can be filled with fire-resistant and flame-retardant materials such as slag wool, or it can be made of high-efficiency flame-retardant glass fiber reinforced plastic.

2. External protection

Avoid accelerated aging and damage to cable insulation

(1) Cable trenches and cable tunnels should have good drainage facilities, such as shallow drainage trenches and water collecting wells, which can effectively drain water. If necessary, set up automatic start and stop water pumping devices to prevent water accumulation and keep the interior dry.

(2) The longitudinal drainage gradient value of cable trenches and tunnels should not be less than 1% to 2%, and should be at least greater than 0.5% to prevent water, corrosive gases or liquids and flammable liquids or gases from entering, cable trenches, and cable tunnels.

(3) The cable tunnel should be naturally ventilated, but when the normal load of the cable makes the air temperature in the tunnel higher than 40℃～50℃, a combination of natural exhaust and mechanical exhaust can be adopted for ventilation. The fan of the ventilation system shall be interlocked with the fire detector to ensure that the air supply can be automatically stopped when a fire occurs in the tunnel. The cable tunnel shall not be used as the air inlet of the ventilation system.

Prevent other equipment from igniting the cable

There are oil-filled electrical equipment and coal handling, pulverizing systems, and gasoline oil systems that can ignite cables. Actions must be taken against them:

(1) The cover plate of the cable trench near the oil-filled electrical equipment should be sealed to prevent the oil from flowing into the cable trench to ignite the cable when the equipment fails and catches fire.

(2) The powder accumulated on the cables near the coal conveying and pulverizing systems should be cleaned regularly to prevent the spontaneous combustion of the coal powder and igniting the cables.

(3) The cables facing the explosion-proof door of the milling system must be packed in a fire-proof box to prevent the fire-proof door from spitting fire and igniting the cable. The cables under the turbine head should be packed in a fireproof box.

Reasonable layout

After analysis, it was found that in some cases, after the cable caught fire, it quickly extinguished itself. This situation is closely related to a reasonable cable layout. When conditions permit, the cables should not be arranged too densely. The primary and secondary cables should be laid in different cable trenches, with good ventilation and heat dissipation in the trenches and away from high-temperature objects.

If there is an unfortunate cable fire, what should be done to reduce the loss as much as possible?

1. Buried sand laying

Buried sand laying obviously has the best fire protection effect. When the cable catches fire, the method of burying sand to extinguish the fire has a very good effect. However, it is not suitable for laying a large number of low-voltage cables. This method is mainly used in high-voltage oil-filled cable lines.

2. Water spray fire extinguishing

The cable line itself is flammable. If a fire or gas explosion occurs, the consequences will be unimaginable, and the cable is generally laid underground or in a cable structure, and the surrounding environment and waterproof measures may also see water, and the hidden danger cannot be dealt with in time. , which will affect the normal operation of the transmission, transformation and distribution system. Therefore, it is very important to do a good job of fire prevention and fire fighting.