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An Automatic Extinguisher for Cable Joints Fire
An Automatic Extinguisher for Cable Joints Fire
【abstract】In this article, in accordance with the fire prevention and extinguishing on cable joints, we put forward a solution and have a discussion about the application
【key word】fire, cable joint, extinguishing bag
1. Fire Introduction
Fire is an extreme accidental issue, since any possible hidden trouble points will not take fire for a long time before the disaster, so it is very difficult to be detected at the very beginning which is just the best timing for putting out a fire. In actual situation, fire is easy to spread despite of any fire barrier areas, due to field limitation. Thus how to take action at the earliest time is the most important thing.
As a traditional solid fire accident, power cables fires mostly distribute widely in crowded areas without proper radiators. Although power cable is not tinder, it is difficult to be put out if taking fire and releases much poisonous gas and heat, which will damage other low-pressure electric equipments and threaten the working staffs.
Just as other fire accidents, due to the indetermination, it is impossible to make comprehensive prevention actions for cable fire. According to cable fire reasons, the probability of cable body short circuit discharge is less than 20%, and the correspondence fire probability is even much lower. The resistance of cable joints is higher than the body, and longtime operation accumulates high heat, which cause short circuit discharge, even fire. Obviously it is much easier and more valuable to prevent any hidden fire possibility for the cable joints firstly.
2 Current Fire Prevention Statuses
2.1 Current prevention equipments for cable joints are including anti-fire tape, anti-fire mud, barrier board, special dope, etc. Extinguishers are traditional way and automatic system. And the surveillance ways are field temperature detector and fire smoke alarm system.
2.2 Seeing from the actual application result, anti-fire tape, mud and dope are useless when the cable joints explode due to short circuit discharge.
2.3 Anti-fire board and slot could control fire spreading for some time, and also have some limitations as following:
2.3.1 Sometimes the cable joints blast will destroy the barrier board, and the possible fire will enkindle the upper stratum cables.
2.3.2 Even the barrier board is not damaged by the blast, it still may be fired under high heat, and then enkindle upper stratum cables.
2.3.3 If the cable slot box is sealed completely, high heat will shorten the cable warranty period. If the cable slot is open, fire will spread along the cables. According to the experiment data, fire could spread from the cable joints at 5 cm/min in horizontal direction without wind help, and the speed will rise to about 15 cm/min in silo!
Hereby we could see above anti-fire ways will not realize the function completely due to field limitations, and they could not put out the fire. The core request is to put out the fire ASAP after the cable joints explode and fire, which could furthest reduce the probability fire accident.
2.4 The normal process of fire fighting is separated to detecting, forward equipments and field operation, which will delay the best timing. On the other side, the smoke detector is easy to alarm by error or left unused, so it will not properly alarm when real fire happens. Forwarding equipments will take much time especially in workshop, underground construction and piles. The above reasons will cause the little fire develop to big fire accident.
2.5 Current fire extinguishers depend on fire smoke and temperature alarm system to give proper fire information, and then start the automatic water spraying system. Some parts of the system may be lack of maintenance or out of work due to power stop during the accident. Besides, the CO2 extinguisher will hurt nearby working staffs if start by error in the daily grind. Moreover the cost of equipment maintenance is very high, while the probability of alarm by error is very high, so it is not suitable to be adopted widely in industry fields.
3. Solution
Hereby I bring forward a unique solution to put out the fire at the earliest time automatically, avoiding big fire accident. In order to put out a fire for the most possible hidden points, this design is a plastic film, filling with sand inside. Hang this set above the hidden fire trouble point, and put an anti-fire board under the hidden fire trouble point. (Graphic 1)
When the hidden trouble point is on fire anytime, the fire burns the plastic film to fuse, and the sand inside will drop on the ground shaping to a cone, separating the combustible from air, which could stop the starting fire and protect nearby equipments.
The amount of sand should be enough to cover the hidden trouble point completely, and the extinguisher vertical projection area should be obviously bigger than the hidden trouble point. (Graphic 2)
The thickness of plastic film should burden the weight of sand in the long run. If the hidden trouble point is too big, metal grid could be used to assist burdening the weight. The hanging height should enable the starting fire burn the plastic film to fuse in a short time.
To avoid the sand is blown by wind, it should be sealed up in the plastic film, and it could be changed to other non-flammable grain or powder.
Besides the fixed hidden fire trouble points, the set could also be used to obstruct fires in different areas in a building, and also block the silo.
4. Application
4.1 Set Features
4.1.1 Thickness of plastic film
It should be very flammable when fire starts, and meanwhile it must burden the weight of sand in the long run, which determines the balance thickness. Despite plastic, other special materials could be considered.
4.1.2 The hanging height
If the height is short, sand will not drop quickly to spread on the fire; and if the height is too high, the burning time for plastic film fusing is too long, and fire may be difficult to terminate.
4.1.3 The amount of sand
If the amount of sand is insufficient, it will not terminate the fire; and if it is too much, it will cover unnecessary space.
Above features could be designed according to field application environment status regularly.
4.2 Humidity of sand
Thru a series simulation experiments, the plastic film that packing sand is more difficult to burn to fuse than a sign plastic film. When fire heats the plastic film, the sand inside will absorb some heat and decrease temperature to postpone the time of plastic film fusing. The idea time of plastic film fusing is about 30 seconds, and the time will be much longer if the sand is wet. The fire fighting results of wet and dry sand are almost same. So it is better to choose dry sand.
4.3 Explosion-proof
It is most primary to prevent exploding in cable fire fighting. Then how powerful on earth is the cable joints short circuit discharge explosion? Till now few people personally experienced the horrible phenomena. This process starts from cable joints temperature rising, and then cable insulation capability declines sharply. The voltaic arc caused by super-high electric potential that may be up to 35 KV or even higher, will instantly resolve the non-flammable high molecular polymer to flammable low molecular compound, and then short circuit discharge appears. The cable joint will explode, and arc will burn combustible to cause serious fire, which will often create interlock damages on other cables or equipments. (Graphic 3)
The actual accident shows that the electric arc in blast will penetrate slim steel board. And for the extinguisher bag, electric arc more possibly damage its bottom than blow it up, since it is considerable heavy with certain volume. In this situation, cable joints will be covered immediately by the sand even before fire starts.
So it is clear that explosion will not affect the extinguisher bag radically, and the key element is the bag should be designed to fix up avoiding certain impact force.
5. Performance Analysis
5.1 Application Features
Features Application
5.2 Unique advantages:
5.2.1 Performance will not be affected by explosion occurs.
5.2.2 Especially adaptive in all terrains including workshop, underground structure and skyscraper, etc.
5.2.3 After traditional fire fighting operation, the field is always in a mess. But if using this extinguisher bag, the original accident appearance will be kept, which is also very helpful to recover fire reason and make proper prevention.
6. Epilogue
Cable fire accident is a kind of human-made disaster, which is absolutely not act of god, so it should be prevent at all time in theory. In safety engineering, the prevention is the primary point, just because human-made disaster could be prevented completely. Although it is impossible to terminate all the fire accidents, we are able to decrease the fire probability close to zero using effective methods.
Author summary: Dai Hengwei was born in 1973, and graduated from electric automatization major of Sichuan University in 1992. He has been working in Power Center of Panzhihua New Steel & Vanadium Company Limited, Sichuan Province for 18 years as a cable department maintenance engineer, joining dozens of fire accident fighting with rich experience.
Appendix: Video http://v.ku6.com/show/CnoiQFEjVJ5rkvla.html
【abstract】In this article, in accordance with the fire prevention and extinguishing on cable joints, we put forward a solution and have a discussion about the application
【key word】fire, cable joint, extinguishing bag
1. Fire Introduction
Fire is an extreme accidental issue, since any possible hidden trouble points will not take fire for a long time before the disaster, so it is very difficult to be detected at the very beginning which is just the best timing for putting out a fire. In actual situation, fire is easy to spread despite of any fire barrier areas, due to field limitation. Thus how to take action at the earliest time is the most important thing.
As a traditional solid fire accident, power cables fires mostly distribute widely in crowded areas without proper radiators. Although power cable is not tinder, it is difficult to be put out if taking fire and releases much poisonous gas and heat, which will damage other low-pressure electric equipments and threaten the working staffs.
Just as other fire accidents, due to the indetermination, it is impossible to make comprehensive prevention actions for cable fire. According to cable fire reasons, the probability of cable body short circuit discharge is less than 20%, and the correspondence fire probability is even much lower. The resistance of cable joints is higher than the body, and longtime operation accumulates high heat, which cause short circuit discharge, even fire. Obviously it is much easier and more valuable to prevent any hidden fire possibility for the cable joints firstly.
2 Current Fire Prevention Statuses
2.1 Current prevention equipments for cable joints are including anti-fire tape, anti-fire mud, barrier board, special dope, etc. Extinguishers are traditional way and automatic system. And the surveillance ways are field temperature detector and fire smoke alarm system.
2.2 Seeing from the actual application result, anti-fire tape, mud and dope are useless when the cable joints explode due to short circuit discharge.
2.3 Anti-fire board and slot could control fire spreading for some time, and also have some limitations as following:
2.3.1 Sometimes the cable joints blast will destroy the barrier board, and the possible fire will enkindle the upper stratum cables.
2.3.2 Even the barrier board is not damaged by the blast, it still may be fired under high heat, and then enkindle upper stratum cables.
2.3.3 If the cable slot box is sealed completely, high heat will shorten the cable warranty period. If the cable slot is open, fire will spread along the cables. According to the experiment data, fire could spread from the cable joints at 5 cm/min in horizontal direction without wind help, and the speed will rise to about 15 cm/min in silo!
Hereby we could see above anti-fire ways will not realize the function completely due to field limitations, and they could not put out the fire. The core request is to put out the fire ASAP after the cable joints explode and fire, which could furthest reduce the probability fire accident.
2.4 The normal process of fire fighting is separated to detecting, forward equipments and field operation, which will delay the best timing. On the other side, the smoke detector is easy to alarm by error or left unused, so it will not properly alarm when real fire happens. Forwarding equipments will take much time especially in workshop, underground construction and piles. The above reasons will cause the little fire develop to big fire accident.
2.5 Current fire extinguishers depend on fire smoke and temperature alarm system to give proper fire information, and then start the automatic water spraying system. Some parts of the system may be lack of maintenance or out of work due to power stop during the accident. Besides, the CO2 extinguisher will hurt nearby working staffs if start by error in the daily grind. Moreover the cost of equipment maintenance is very high, while the probability of alarm by error is very high, so it is not suitable to be adopted widely in industry fields.
3. Solution
Hereby I bring forward a unique solution to put out the fire at the earliest time automatically, avoiding big fire accident. In order to put out a fire for the most possible hidden points, this design is a plastic film, filling with sand inside. Hang this set above the hidden fire trouble point, and put an anti-fire board under the hidden fire trouble point. (Graphic 1)
When the hidden trouble point is on fire anytime, the fire burns the plastic film to fuse, and the sand inside will drop on the ground shaping to a cone, separating the combustible from air, which could stop the starting fire and protect nearby equipments.
The amount of sand should be enough to cover the hidden trouble point completely, and the extinguisher vertical projection area should be obviously bigger than the hidden trouble point. (Graphic 2)
The thickness of plastic film should burden the weight of sand in the long run. If the hidden trouble point is too big, metal grid could be used to assist burdening the weight. The hanging height should enable the starting fire burn the plastic film to fuse in a short time.
To avoid the sand is blown by wind, it should be sealed up in the plastic film, and it could be changed to other non-flammable grain or powder.
Besides the fixed hidden fire trouble points, the set could also be used to obstruct fires in different areas in a building, and also block the silo.
4. Application
4.1 Set Features
4.1.1 Thickness of plastic film
It should be very flammable when fire starts, and meanwhile it must burden the weight of sand in the long run, which determines the balance thickness. Despite plastic, other special materials could be considered.
4.1.2 The hanging height
If the height is short, sand will not drop quickly to spread on the fire; and if the height is too high, the burning time for plastic film fusing is too long, and fire may be difficult to terminate.
4.1.3 The amount of sand
If the amount of sand is insufficient, it will not terminate the fire; and if it is too much, it will cover unnecessary space.
Above features could be designed according to field application environment status regularly.
4.2 Humidity of sand
Thru a series simulation experiments, the plastic film that packing sand is more difficult to burn to fuse than a sign plastic film. When fire heats the plastic film, the sand inside will absorb some heat and decrease temperature to postpone the time of plastic film fusing. The idea time of plastic film fusing is about 30 seconds, and the time will be much longer if the sand is wet. The fire fighting results of wet and dry sand are almost same. So it is better to choose dry sand.
4.3 Explosion-proof
It is most primary to prevent exploding in cable fire fighting. Then how powerful on earth is the cable joints short circuit discharge explosion? Till now few people personally experienced the horrible phenomena. This process starts from cable joints temperature rising, and then cable insulation capability declines sharply. The voltaic arc caused by super-high electric potential that may be up to 35 KV or even higher, will instantly resolve the non-flammable high molecular polymer to flammable low molecular compound, and then short circuit discharge appears. The cable joint will explode, and arc will burn combustible to cause serious fire, which will often create interlock damages on other cables or equipments. (Graphic 3)
The actual accident shows that the electric arc in blast will penetrate slim steel board. And for the extinguisher bag, electric arc more possibly damage its bottom than blow it up, since it is considerable heavy with certain volume. In this situation, cable joints will be covered immediately by the sand even before fire starts.
So it is clear that explosion will not affect the extinguisher bag radically, and the key element is the bag should be designed to fix up avoiding certain impact force.
5. Performance Analysis
5.1 Application Features
Features Application
5.2 Unique advantages:
5.2.1 Performance will not be affected by explosion occurs.
5.2.2 Especially adaptive in all terrains including workshop, underground structure and skyscraper, etc.
5.2.3 After traditional fire fighting operation, the field is always in a mess. But if using this extinguisher bag, the original accident appearance will be kept, which is also very helpful to recover fire reason and make proper prevention.
6. Epilogue
Cable fire accident is a kind of human-made disaster, which is absolutely not act of god, so it should be prevent at all time in theory. In safety engineering, the prevention is the primary point, just because human-made disaster could be prevented completely. Although it is impossible to terminate all the fire accidents, we are able to decrease the fire probability close to zero using effective methods.
Author summary: Dai Hengwei was born in 1973, and graduated from electric automatization major of Sichuan University in 1992. He has been working in Power Center of Panzhihua New Steel & Vanadium Company Limited, Sichuan Province for 18 years as a cable department maintenance engineer, joining dozens of fire accident fighting with rich experience.
Appendix: Video http://v.ku6.com/show/CnoiQFEjVJ5rkvla.html
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