Discussion on Fire Protection Technology of Power Cable
Due to the flammability and stringiness of the cables, in the event of a fire, the hazards are 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 their role is to transmit and distribute electrical energy. The power cable is composed of insulated core wire, insulation sheath and 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 performance. However, when overcurrent occurs in the cable circuit and the cable is overheated, the performance of the cable changes and a fire is then generated. This article intends to discuss the fire protection technology of the cable.
1, create a good operating environment to avoid cable insulation accelerated aging and damage cable trenches, cable tunnels should have good drainage facilities, such as the setting shallow shallow ditch, water collection wells, and effective drainage, if necessary, set up automatic start and stop pumping devices, Prevent water supply and keep interior dry. Cable trenches and tunnels maintain drainage slopes in the longitudinal direction. Prevent water, corrosive gases or liquids, and flammable liquids or gases from entering the cable trenches and cable tunnels. The cable tunnel should be naturally ventilated. When the normal load of the cable is used so that the air temperature in the tunnel is higher than 40 to 50°C, natural ventilation and mechanical exhaust can be used for ventilation. Ventilation system fan should be linked with the fire detector to ensure that the tunnel can automatically stop the wind when the fire occurs, the cable tunnel shall not be used as ventilation system inlet.
The practice of influencing the ventilation and heat dissipation of the cable should be avoided by keeping the fire door of the cable in the normally closed state, completely blocking the cable with a fireproof partition, and filling and sealing the gap of the cable trench cover. Moreover, the complete closure of the cable also makes it impossible to perform normal inspections of the cable and cannot detect cable faults in time.
In addition, there must be sound facilities to prevent rodents and snakes from entering and prevent small animals from destroying cable insulation and causing accidents.
2. Strengthen the cable's preventive test cable After the cable and cable accessories are installed, perform a DC voltage withstand test [preventive test]. Compare and analyze experimental data. That is, it can be compared with the experimental data of the same cable, and can also be compared with the historical data of the cable to explore the laws of experimental data. If a DC withstand voltage test is performed, the measured leakage current has one of the following conditions, and the cable insulation may be defective, reflecting the defect site and handling it:
(1) It rises faster with the increase of the test voltage value or the increase of the pressure time;
(2) Compared with the same cable, the value increases more;
(3) Compared with the previous data measured by this cable, there is a clear upward trend;
(4) The leakage current imbalance coefficient between three phases is large.
The above conditions should be carefully analyzed if the non-test method caused by improper income, you can increase the experimental voltage or extend the test time to determine whether the cable meets the conditions for continued operation.
For the DC withstand voltage test standard for power cables, see Chapter 17 of "Electrical Installation Installation Engineering Electrical Equipment Transfer Test Standards" (GB50150-91). The DC withstand voltage test value of a commonly used plastic insulated power cable is 4 times the rated voltage of the cable; the test time is 15 minutes.
3. Strong management and operation monitoring of cable head production quality According to statistics, cable fires and explosions caused by cable head failures account for about 70% of total cable accidents. The material and process quality of the empty cable head must be strictly controlled. The service life of the manufactured cable head must not be lower than the service life of the cable. The rated voltage level on the street and its insulation level must not be lower than the rated voltage level of the connected cable and its insulation level. The withstand voltage between the insulation mats on both sides of the insulation head shall not be less than 2 times the insulation level of the cable protective layer. The joint form should be compatible with the set environmental conditions, and it will not affect the capacity of the cable. Within the range of 2~3m on both sides of the cable head, fireproof tapes shall be used for fire retarding and burning treatment.
In general, cables look at the weak links of cable insulation, so strengthening the monitoring and management of cable heads is an important part of cable fire protection. The terminal cable head must not be placed in the cable trench, cable tunnel, cable tray box, and the intermediate cable gland in the cable jacket. It must be registered and used with various detection devices. When the cable head is found to have abnormal temperature rise or odor and smoke, the emergency exits early to avoid running on fire.
Between the intermediate cable heads should ensure a sufficient safety distance, more than two cable heads placed in the same position, between the cable head and other cables should take strict sealing measures.
4, to prevent other equipment fire ignition cable ignitable cable ignition oil-filled electrical equipment and coal handling, milling system, gasoline engine system. For them, corresponding measures must be taken: the cable trench cover near the oil-filled electrical equipment should be sealed, and the textile equipment flow to the cable trench to ignite the cable when the textile equipment fails to catch fire. The powder on the cable near the coal conveying and pulverizing system should be regularly cleaned to prevent the pulverized coal from spontaneously igniting the cable. The anti-riot door of the pulverizing system must have a fireproof slot box for the cable facing the explosion preventing the explosion-proof door action to ignite the ignition cable.
5, with the seal, plugging, coating, package and other measures to prevent the cable flame retardant fire retardant coating has a thin coating, does not affect the normal heat dissipation, while also playing a good thermal insulation and flame retardant effect, but there are many defects. Including improper selection of fire-retardant paint varieties, the market is in the fake and shoddy products for ten days; the practical application of the use of poor results, the surface of the ejection material there are peeling off, uneven coating thickness, cutting corners and so on.
The fire protection coating used in cable engineering is mainly solvent-based. Solvent-based solvents have problems in terms of toxicity, price, transportation safety, and ring contamination. Application effects such as cold resistance, water resistance, and oil resistance are not ideal. In particular, the bending resistance is not good, and the flexibility of the coating after curing is also poor, and it is only applicable to a fixedly mounted cable, and the coating is easily dried and peeled off.
Therefore, when the cable is not suitable for flame retardant use of a large number of fire-retardant paints, a large number of sealing, plugging, and blocking methods should be used. The following issues should be noted:
(1) The method of sealing, blocking, and separating must be used to ensure that a single cable catches fire and does not extend multiple cables. Cables entering the trenches, cable tunnels, cable trays, and cable jackets must be tightly sealed to prevent the ignition of a single cable or a small number of cables and ignite a large number of cables. A fire wall and fire door should be installed every 60 to 100 meters in cable trenches and cable tunnels. Fire barriers should be set up in the shaft. Fire barriers should be installed between the power cables and control cables. Control cables should be fireproofed or used. Fire-retardant cables to ensure that the main equipment can be safely stopped in any emergency.
Important cable channels should be equipped with automatic alarm and automatic fire extinguishing devices, such as water spray and water mist fire extinguishing devices, to achieve early detection and early suppression.
(2) The tightness and thickness of the fireproof plug must be guaranteed. If the fire blocking is not tight, the sealing effect will be lost, especially where the cables are concentrated, and soft plugging is used to ensure tight sealing. During the maintenance inspection, the damaged plugging should be restored in time. The thickness of the plugging material is not enough, and the fire will burn through the plugged material after the cable catches fire. The thickness of the plugging material should be in direct proportion to the number of plugged cables, and the more the cable, the thicker the blockage. Fire doors should be automatically closed after a fire.
(3) The fireproof plugging layer must be purchased with mechanical strength. Because the cable catches fire, especially the electric short circuit, will cause the air to swift and violently to expand to produce certain impulse, destroys the fireproof plugging layer with low mechanical strength, causes the fireproof plugging to lose the function.
(4) The fireproof plugging material is commonly used fireproof rock wool, asbestos board, asbestos rope, fireproof mortar and more advanced high-tech materials. The construction unit should select suitable materials according to the actual conditions of each project and different fireproof areas. And plugging methods. The main parts of plugging are high voltage and low voltage configuration electric rooms, power distribution shafts, fire control rooms, cable bridges, and power distribution lines that pass through the floor of the floor. Because of the flammability and stringiness of the cables, once the fire occurs, the damage is serious, especially In a power plant and a large substation, in the event of a fire, other circuits are affected. 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 their role is to transmit and distribute electrical energy. The power cable is composed of insulated core wire, insulation sheath and 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 performance. However, when overcurrent occurs in the cable circuit and the cable is overheated, the performance of the cable changes and a fire is then generated. This article intends to discuss the fire protection technology of the cable.
1, create a good operating environment to avoid cable insulation accelerated aging and damage cable trenches, cable tunnels should have good drainage facilities, such as the setting shallow shallow ditch, water collection wells, and effective drainage, if necessary, set up automatic start and stop pumping devices, Prevent water supply and keep interior dry. Cable trenches and tunnels maintain drainage slopes in the longitudinal direction. Prevent water, corrosive gases or liquids, and flammable liquids or gases from entering the cable trenches and cable tunnels. The cable tunnel should be naturally ventilated. When the normal load of the cable is used so that the air temperature in the tunnel is higher than 40 to 50°C, natural ventilation and mechanical exhaust can be used for ventilation. Ventilation system fan should be linked with the fire detector to ensure that the tunnel can automatically stop the wind when the fire occurs, the cable tunnel shall not be used as ventilation system inlet.
The practice of influencing the ventilation and heat dissipation of the cable should be avoided by keeping the fire door of the cable in the normally closed state, completely blocking the cable with a fireproof partition, and filling and sealing the gap of the cable trench cover. Moreover, the complete closure of the cable also makes it impossible to perform normal inspections of the cable and cannot detect cable faults in time.
In addition, there must be sound facilities to prevent rodents and snakes from entering and prevent small animals from destroying cable insulation and causing accidents.
2. Strengthen the cable's preventive test cable After the cable and cable accessories are installed, perform a DC voltage withstand test [preventive test]. Compare and analyze experimental data. That is, it can be compared with the experimental data of the same cable, and can also be compared with the historical data of the cable to explore the laws of experimental data. If a DC withstand voltage test is performed, the measured leakage current has one of the following conditions, and the cable insulation may be defective, reflecting the defect site and handling it:
(1) It rises faster with the increase of the test voltage value or the increase of the pressure time;
(2) Compared with the same cable, the value increases more;
(3) Compared with the previous data measured by this cable, there is a clear upward trend;
(4) The leakage current imbalance coefficient between three phases is large.
The above conditions should be carefully analyzed if the non-test method caused by improper income, you can increase the experimental voltage or extend the test time to determine whether the cable meets the conditions for continued operation.
For the DC withstand voltage test standard for power cables, see Chapter 17 of "Electrical Installation Installation Engineering Electrical Equipment Transfer Test Standards" (GB50150-91). The DC withstand voltage test value of a commonly used plastic insulated power cable is 4 times the rated voltage of the cable; the test time is 15 minutes.
3. Strong management and operation monitoring of cable head production quality According to statistics, cable fires and explosions caused by cable head failures account for about 70% of total cable accidents. The material and process quality of the empty cable head must be strictly controlled. The service life of the manufactured cable head must not be lower than the service life of the cable. The rated voltage level on the street and its insulation level must not be lower than the rated voltage level of the connected cable and its insulation level. The withstand voltage between the insulation mats on both sides of the insulation head shall not be less than 2 times the insulation level of the cable protective layer. The joint form should be compatible with the set environmental conditions, and it will not affect the capacity of the cable. Within the range of 2~3m on both sides of the cable head, fireproof tapes shall be used for fire retarding and burning treatment.
In general, cables look at the weak links of cable insulation, so strengthening the monitoring and management of cable heads is an important part of cable fire protection. The terminal cable head must not be placed in the cable trench, cable tunnel, cable tray box, and the intermediate cable gland in the cable jacket. It must be registered and used with various detection devices. When the cable head is found to have abnormal temperature rise or odor and smoke, the emergency exits early to avoid running on fire.
Between the intermediate cable heads should ensure a sufficient safety distance, more than two cable heads placed in the same position, between the cable head and other cables should take strict sealing measures.
4, to prevent other equipment fire ignition cable ignitable cable ignition oil-filled electrical equipment and coal handling, milling system, gasoline engine system. For them, corresponding measures must be taken: the cable trench cover near the oil-filled electrical equipment should be sealed, and the textile equipment flow to the cable trench to ignite the cable when the textile equipment fails to catch fire. The powder on the cable near the coal conveying and pulverizing system should be regularly cleaned to prevent the pulverized coal from spontaneously igniting the cable. The anti-riot door of the pulverizing system must have a fireproof slot box for the cable facing the explosion preventing the explosion-proof door action to ignite the ignition cable.
5, with the seal, plugging, coating, package and other measures to prevent the cable flame retardant fire retardant coating has a thin coating, does not affect the normal heat dissipation, while also playing a good thermal insulation and flame retardant effect, but there are many defects. Including improper selection of fire-retardant paint varieties, the market is in the fake and shoddy products for ten days; the practical application of the use of poor results, the surface of the ejection material there are peeling off, uneven coating thickness, cutting corners and so on.
The fire protection coating used in cable engineering is mainly solvent-based. Solvent-based solvents have problems in terms of toxicity, price, transportation safety, and ring contamination. Application effects such as cold resistance, water resistance, and oil resistance are not ideal. In particular, the bending resistance is not good, and the flexibility of the coating after curing is also poor, and it is only applicable to a fixedly mounted cable, and the coating is easily dried and peeled off.
Therefore, when the cable is not suitable for flame retardant use of a large number of fire-retardant paints, a large number of sealing, plugging, and blocking methods should be used. The following issues should be noted:
(1) The method of sealing, blocking, and separating must be used to ensure that a single cable catches fire and does not extend multiple cables. Cables entering the trenches, cable tunnels, cable trays, and cable jackets must be tightly sealed to prevent the ignition of a single cable or a small number of cables and ignite a large number of cables. A fire wall and fire door should be installed every 60 to 100 meters in cable trenches and cable tunnels. Fire barriers should be set up in the shaft. Fire barriers should be installed between the power cables and control cables. Control cables should be fireproofed or used. Fire-retardant cables to ensure that the main equipment can be safely stopped in any emergency.
Important cable channels should be equipped with automatic alarm and automatic fire extinguishing devices, such as water spray and water mist fire extinguishing devices, to achieve early detection and early suppression.
(2) The tightness and thickness of the fireproof plug must be guaranteed. If the fire blocking is not tight, the sealing effect will be lost, especially where the cables are concentrated, and soft plugging is used to ensure tight sealing. During the maintenance inspection, the damaged plugging should be restored in time. The thickness of the plugging material is not enough, and the fire will burn through the plugged material after the cable catches fire. The thickness of the plugging material should be in direct proportion to the number of plugged cables, and the more the cable, the thicker the blockage. Fire doors should be automatically closed after a fire.
(3) The fireproof plugging layer must be purchased with mechanical strength. Because the cable catches fire, especially the electric short circuit, will cause the air to swift and violently to expand to produce certain impulse, destroys the fireproof plugging layer with low mechanical strength, causes the fireproof plugging to lose the function.
(4) The fireproof plugging material is commonly used fireproof rock wool, asbestos board, asbestos rope, fireproof mortar and more advanced high-tech materials. The construction unit should select suitable materials according to the actual conditions of each project and different fireproof areas. And plugging methods. The main parts of plugging are high voltage and low voltage configuration electric rooms, power distribution shafts, fire control rooms, cable bridges, and power distribution lines that pass through the floor of the floor. Because of the flammability and stringiness of the cables, once the fire occurs, the damage is serious, especially In a power plant and a large substation, in the event of a fire, other circuits are affected. Therefore, the fire protection technology of power cables is one of the important technologies for the normal operation of electrical systems.
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