The reasons why fireproof wires and hrrf cables cause fire in coal mine

Frequently cable or wire fire caused coal mine accidents, heavy lessons, in particular the fireproof wires and hrrf cables. The purpose of this article is to study and summarize the causes of cable fire and the preventive measures, and at the same time to give buyers some effective suggestions when they are planning to have a procurement whoever you are wholesalers or project contractors.  

The main causes of cable fire accidents  

1. External fire causes the cable to catch fire. The poor underground conditions of coal mine (such as high temperature, high humidity, poor heat dissipation, etc.) lead to the failure and damage of electrical equipment, causing the combustion of the electrical equipment itself, so as to ignite the fireproof wires and cables connected with the electrical equipment or laid around the cable, causing a fire.  

2. Cable overcurrent causes cable heating and fire. Rubber sheathed cable, hrrf cables and shielded cable because there is no reliable protection against mechanical damage, vulnerable to rock, mining machinery and tools damage, resulting in water and dust infiltration into the cable, and then short circuit fire;  Mechanical damage to the insulation of armored cable in use will lead to the breakdown of the insulation between the cable phase line or between the phase line and the steel armor and arc, resulting in the fire of the insulation material and cable jacket; Cable overload work for a long time, will lead to insulation performance decline or even lose insulation performance, resulting in cable insulation breakdown fire;  When the current suddenly increases due to equipment failure, the electromagnetic starter and feeder switch do not operate, resulting in a sharp rise in cable temperature, leading to insulation breakdown and fire.  

3. Cable connection failure leads to large joint resistance, causing local high temperature (arc) fire. The cable connector is the weakest link in the circuit. If the connection between the cable core and the wiring terminal of the electrical equipment is not reliable, it is very easy to arc the terminal post and cable head due to the small contact area, causing fire. The humidity of underground air is generally more than 95%, and the cable junction box is easy to be affected by moisture. If the junction box is poorly sealed and leaks into moisture, insulation breakdown can be caused, resulting in short circuit and fire.  

4. Cable aging, insulation, voltage resistance, current capacity and other properties reduce the cable insulation aging cause fire.  The essence of cable insulation aging is the irreversible change of material properties. Firstly the cable insulation layer in use is normal aging, if not replaced in time is easy to cause fire; Secondly is not normal use, the cable in overload or external damage caused by short circuit leakage, will accelerate the aging of cable insulation, resulting in cable short circuit fire.  

5. Use non-fireproof wires and cable to delay ignition of local ignition point. Non-fireproof wires and cables are made of ordinary PVC. When the cable is ignited, it generates a lot of combustion heat. After the external fire source is removed, the heat value released is greater than the sum of preheating and heat dissipation required for combustion, and the combustion is flourishing.  So once the non-fireproof wire or cable is ignited, even a small spark can make the fire spread quickly and cause a fire. Underground coal mine belongs to inflammable and explosive places, the use of non-flame retardant cable in underground coal mine will undoubtedly bury a time bomb.  

Cable fire accident prevention measures  

1. Preventive measures of external fire sources. Regulate downhole operation to prevent non-standard operation that may cause electrical equipment to catch fire;  Establish a sound fire monitoring and early warning system.  

2. Preventive measures of cable overcurrent. Reasonable use of overcurrent, leakage protection device, in the cable overcurrent, short circuit or leakage, can timely action, cut off the source of failure, prevent accidents.  According to the actual situation of the mine correctly calculate and set the setting value of overcurrent protection device, regular maintenance, according to the actual distributed capacitance of underground power grid reasonable installation of leakage protection device, can prevent cable leakage caused by the phase of short circuit fault;  Pay attention to the influence of cable installation quality and laying environment. Cable support and hanging should be reasonable to avoid damage to cable sheath and insulation.  According to the load of the power supply circuit and the requirements of the use place, select fireproof wires and hrrf cables with appropriate cross-sectional area to prevent long-term overload of cables.

3. Preventive measures for cable joint failure. The connection of hrrf cables and electrical equipment must use junction boxes consistent with the performance of electrical equipment. The cable core must be connected with the electrical equipment by toothed pressing plate (clamp) or line nose. The protective grade of the shell of the cable junction box must meet the requirements of long-term underground damp and dust environment.  

4. Cable aging prevention measures. The establishment of strict cable aging management mechanism, regular cable insulation withstand voltage test; For hrrf cables with aging insulation layers, first is to re-check whether the selection of cross-sectional area is reasonable, second is to check whether the hrrf cable model matches the application environment, and three is to replace and repair in time.  

Non fireproof wires and cables are strictly prohibited. cables used in underground coal mines must be flame retardant cables with safety marks for coal mine products ,non-fireproof wires and cables are strictly prohibited to be used in underground coal mines, what's more the hffr cables are necessary for the cabling.  

Cable safety protection system  

1. Comply with regulations and use fireproof wires and cables. Fireproof wires or cable refers to the cable in which the sample is ignited under specified test conditions and the flame spread is only within a limited range after the test fire source is removed, and the residual flame or residual burning can be extinguished within a limited time. As can be seen from the definition of fireproof wire or cable, "fireproof wire or cable" is not "non-combustible cable". Even if fireproof wire is used underground in coal mine, if other electrical appliances are not fully protected or there is an external fire source,fireproof wire or cable will burn.  

2. Scientific design, standardized procurement. The design of the whole system should start from the whole, according to the load of the power supply line and the requirements of the place of use, in addition to the selection of appropriate specifications and cross-sectional area of hrrf cable and fireproof wire or cable, select the appropriate capacity of the load and electrical protection device is also very necessary. There should be over-current and leakage protection devices in the circuit where the electrical equipment is located to prevent accidents.  

3. Reasonable use and regular maintenance. In the limited space and harsh environment underground, the space factor should be taken into consideration when laying cables and installing other electrical equipment to ensure that the electrical equipment has a good heat dissipation channel, so as to avoid the combustion of electrical equipment due to the delay in heat dissipation and damage to the hrrf cable.  

Fireproof Wires and hrrf Cable Selection

Fireproof wires and hrrf cable has been more and more popular recently and for a buyer, how to find a reliable supplier or manufacturer also become more and more important. TOP3 manufacturer in China JZD Cable has been manufacturing fireproof wires and hrrf cables for 12 years. 4 years ago, we exported to foreign market, such as Australia, what's more we applied the SAA certification successfully.

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