1 Introduction With the development of our country's love of the national economy and the improvement of people's living standards, China's industrial electricity and household electricity consumption has increased year by year. In 2010, China's total electricity consumption reached 419.2 billion kWh, a year-on-year increase. 14.56%. A variety of electrical equipment has been increasing and has been applied to all areas of society, which has brought great convenience to people's life and production, but also left more security risks. According to the 2008-2010 China Fire Yearbook, there were 429,738 fires in China in 2007-2009, of which 125,947 electric fires accounted for 29.3% of the total number of fires, which was the main cause of fire. It has been in the first place for many years and remains high, causing huge property losses. In order to curb the occurrence of electrical fires, relevant departments have successively formulated and revised relevant national standards and regulations, emphasizing the protective role of electrical fire monitoring systems in preventing electrical fires caused by ground faults. For example, Article 9.5.1 of "Code for Fire Protection Design of High-rise Civil Buildings" (GB50045-2005) and Section 11.2.7 of "Code for Fire Protection of Building Design" (GB50016-2006) stipulate the places where electrical fire monitoring systems should be installed. The composition and design requirements of the electrical fire monitoring system are specified in the Electrical Fire Monitoring System (GB14287-2005).
2 reasons for electrical fires There are many reasons for electrical fires, such as short circuit, insulation aging, overcurrent, ground fault, poor contact, home appliances or electric heating equipment to ignite combustibles. In essence, in all electrical fire causes, the short-circuit is caused by a short circuit, and 90% of the short-circuit fire is caused by a gradual fault. Gradual faults have a development process, and the ability to release during this process is directly expressed as temperature or arc, which is essentially an increase in leakage current. The development of faults such as overcurrent load, poor contact, home appliances or electric heating equipment is also accompanied by an increase in leakage current. Because the leakage current is relatively small, it is often not enough to make the overcurrent protection device (circuit breaker, fuse) operate. The local high temperature generated by the leakage arc of several hundred milliamperes is more than 2000 °C, which is enough to ignite the surrounding combustibles and cause fire. Concealment often leads to fires.
The cause of such electrical fires is caused by abnormal leakage currents (even small values). It is a hidden fault. If it is not known by certain technical means, the continuous occurrence of the fault may eventually occur. Will cause an electrical fire accident. Therefore, it is necessary to have a device for detecting the residual current (also known as leakage current or leakage current) in the line, which is used to measure the electrical parts in the electrical insulation between the metal parts, or the live parts and the grounding parts. In the meantime, through the current formed by the surrounding medium or the insulating surface, the early warning of such electrical fires can be realized, and the purpose of eliminating fire hazards can be achieved.
3Electrical fire monitoring system The electric fire monitoring system refers to a system that can issue an alarm signal, a control signal and can indicate the alarm location when the detected parameter in the protected line exceeds the alarm set value. The electrical fire monitoring system is a means of electrical fire prevention. It is a real-time monitoring system that acts before the occurrence of electrical fires. It is responsible for the task, function and technical means of the "automatic fire alarm system" after the fire has occurred. All aspects are different, and the two cannot be confused and replaced.
The "ARCM" electrical fire monitoring system is independently developed and produced by Shanghai Ankerui Electric Co., Ltd., including Acrel-6000 electrical fire monitoring system software and ARCM series electrical fire monitoring detectors. It is a new generation of electrical fire monitoring products applied in the dual fields of civil construction and industrial construction. It has the characteristics of ultra-early, high intelligence, miniaturization, multi-function, high reliability, simple and practical. The device is based on a large amount of valuable experience accumulated over the years by the company's system integration projects in the industrial and civil construction fields at home and abroad. The monitoring equipment is designed and developed by industrial computer, has good reliability, and optimizes the human-computer interaction function, making the whole system easy to install, debug and maintain. The host adopts bus data transmission mode and is equipped with residual current type electric fire monitoring. The detectors form a large-capacity electrical fire monitoring system for real-time monitoring and prevention of early electrical fires in high-rise buildings and various industrial sites.
3.1 Basic Principles of Monitoring System The electrical fire monitoring system integrates monitoring, alarming, control and centralized management. The bus is generally connected to a monitoring detector or monitoring unit to communicate with the host and transmit all data collection information. The host collects the received data, monitors the changes of the three-phase current, residual current, temperature, voltage and other parameters of the detected electrical circuit, and feedbacks the current loop status and other information. When an abnormality occurs in the measured line, the electrical fire monitoring detector collects signals through the tools such as transformers and temperature sensors, and sends an alarm signal when the monitored value exceeds the set threshold and reaches the trigger time, and the alarm signal is uploaded to the monitoring device. In the further identification and judgment, the monitoring host issues a fire alarm signal, the alarm indicator lights up, the alarm sounds with a card, and an alarm message is displayed on the display screen, the alarm position is specified, the on-duty personnel quickly perform the inspection process, and the alarm information is sent to the centralized control. At the same time, the duty personnel can also control the equipment to cut off the faulty loop power through the monitoring equipment, and link other fire-fighting equipment to prevent the occurrence of electrical fires.
3.2 The basic components of the monitoring system The electrical fire monitoring system (GB14287) gives the definition and basic components of the electrical fire monitoring system. The electric fire monitoring system is a system that can issue an alarm signal, a control signal and can indicate an alarm part when the detected parameter in the protected line exceeds the alarm set value, and is composed of an electrical fire monitoring device and an electrical fire monitoring detector.
The electrical fire monitoring system developed by Shanghai Anke Rui Electric Co., Ltd. mainly includes: Acrel6000 electrical fire monitoring equipment and ARCM series electrical fire monitoring detectors. Depending on the size of the project, different system solutions are available to achieve better and better goals. Generally we are divided into: small single building; large single building; large group building. The basic system structure diagram for each type of project is given.
Taking the electrical fire monitoring system of a station in Shanghai Rail Transit Line 11 as an example, the project has a total of 196 ARCM200 residual current electrical fire detectors in 5 districts, and communicates with 2 monitoring devices via RS485 bus (1) A 4-port, a 16-port), combined with the monitoring center duty room to form a fire monitoring system (), using the Acrel-6000 system configuration software, with centralized scheduling, control, protection, monitoring, display and other functions, electricity security The advantages of management, analysis and recording in one intelligence can greatly reduce the incidence of electrical fires in applications. 
4 Precautions 4.1 Applicable to electrical fire monitoring system Distribution system protection grounding form 1) Distribution system grounding form TN system definition: The power system has a little grounding, the exposed conductor of the electrical device is connected to the location through the protection line .
The TN system can be divided into: TN-S system, the neutral line (N line) and the protection line (PE line) of the whole system are separated; in the TN-C system, the neutral line and the protection line of the whole system are unified. In the TN-CS system, a part of the neutral and protection lines in the system are unified.
Definition of TT system: There is a point in the power system that is directly grounded. The exposed conductive part of the electrical device is independent of the power system grounding point through the protective grounding wire.
2) Problems that should be paid attention to in different grounding systems. When installing residual current type electric fire monitoring detectors, N lines and PE lines must be strictly distinguished. Three-wire four-wire or four-pole four-wire type N lines should be connected to residual current mutual inductance. Device. The N wire through the transformer shall not be used as a PE wire. It shall not be grounded repeatedly or the device may be exposed to the conductor.
In the TN system, the TN-C system must be retrofitted to TN-CS, TN-S system or partial TT system before the residual current type electrical fire monitoring detector can be installed. In the TN-CS system, the monitoring detector is only allowed to use a separate part of the N line from the PE line.
4.2 Installation of residual current transformer 1) Residual current transformer threading residual current transformer should distinguish the phase line, N line and PE line in the power grid before threading. The phase line and the N line must pass through the residual current transformer together, and the PE line cannot pass through the transformer. In the system, if the N line does not pass through the transformer together with the phase line, once the three-phase load is unbalanced, a current will flow through the N line, and the detector detects the current signal, that is, a malfunction occurs. The N lines between different circuits are not connected or grounded repeatedly. Otherwise, it will cause malfunction. When the system is running, the leakage current value is too large and an alarm occurs. A large part is caused by such a situation. If the PE line passes through the transformer together with the N line and the phase line, it will also cause the rejection or malfunction of the monitoring detector.
Not all residual current monitoring needs to penetrate the phase line into the transformer. The total residual current monitoring method of the TN-S system can be excluded. It can pass only one cable through the residual current transformer. The advantage of this method is that a small residual current transformer can be used to improve the measurement accuracy; in the later stage, if the transformer fails, the maintenance is convenient. The specific wiring diagram is as follows.
For the protected line as the power line, in order to avoid the large-scale equipment starting instantaneous ground leakage current caused by the device alarm action, the monitoring detector's action time should be extended to avoid the abnormal leakage when the device starts, to prevent malfunction.
Hierarchical protection application principles. System applications often have hierarchical protection, common 2 to 3 levels, the selection principle of the upper and lower levels: in terms of operating current, the setting of the upper device must be at least twice that of the lower device; in terms of the trip time, the delay time of the upper device should be greater than The operating time of the primary residual current protection device, and the difference of the action time shall not be less than 0.2s.
Residual current electrical fire monitoring detectors are generally not used alone, but are used in conjunction with electrical fire monitoring equipment. When a leakage fault occurs, there is no immediate fire. If the power supply of the protected object is automatically cut off when the monitoring detector is protected, it may cause other unpredictable hazards. Therefore, the residual current type electrical fire monitoring detector should be used for alarms, and it is not appropriate to automatically cut off the power. When there is an electrical fire monitoring device, the fault information is reported to the host device, and the attendant confirms the fault information and performs the next operation according to the actual situation.
4.4 Leakage fault check Residual current type electric fire monitoring detectors are generally installed at the outlet end of the power system distribution cabinet (transformation station) or the floor distribution box incoming line. When a fault occurs in a protected line or equipment, the point or location of the specific fault cannot be determined. It is also a cumbersome task to check each line and equipment after the installation point one by one.
First, the cause of the leakage fault is caused by improper wiring or wiring errors, or equipment or line failure or new load. In the new operation project, many cases are caused by improper wiring or wiring errors. At this time, the wiring of the protection circuit needs to be corrected one by one. After the equipment in the protected line is in normal operation, if the residual current value is within the expected range, it can be basically determined that the line is normal. The residual current caused by wiring errors tends to be large.
Secondly, the specific parts of the leakage are detected by means of meter detection method, separate power-off method (one by one elimination method), and power failure measurement method. One of the most effective and convenient methods is the separate power-off method, which can narrow down the fault location one by one and finally find the cause of the fault. In the case that power outages are not allowed, we generally use observation methods and meter measurements. Observing method is mainly to observe whether there is obvious wiring error or arcing phenomenon in the line; in the instrument detection method, we need to have a special hand-held leakage detecting device to detect the size of leakage in each circuit and locate according to the size.
5 Conclusion With the development of China's economy and society, electrical safety has attracted more and more attention, and people have gradually realized that electrical fire monitoring systems play an important role in preventing the occurrence of electrical fires in the early stage. Early countries introduced relevant technical standards to regulate the design and construction of electrical fire monitoring systems, which led to the current chaos in the industry and the system's effects did not achieve the intended purpose. At present, these products have been confirmed to be included in the second batch of fire-fighting products that implement compulsory product certification. They will be included in the national CCC-certified products from January 1, 2013. This shows that the relevant national departments can regulate the quality of such products and market confidence. .
2 reasons for electrical fires There are many reasons for electrical fires, such as short circuit, insulation aging, overcurrent, ground fault, poor contact, home appliances or electric heating equipment to ignite combustibles. In essence, in all electrical fire causes, the short-circuit is caused by a short circuit, and 90% of the short-circuit fire is caused by a gradual fault. Gradual faults have a development process, and the ability to release during this process is directly expressed as temperature or arc, which is essentially an increase in leakage current. The development of faults such as overcurrent load, poor contact, home appliances or electric heating equipment is also accompanied by an increase in leakage current. Because the leakage current is relatively small, it is often not enough to make the overcurrent protection device (circuit breaker, fuse) operate. The local high temperature generated by the leakage arc of several hundred milliamperes is more than 2000 °C, which is enough to ignite the surrounding combustibles and cause fire. Concealment often leads to fires.
The cause of such electrical fires is caused by abnormal leakage currents (even small values). It is a hidden fault. If it is not known by certain technical means, the continuous occurrence of the fault may eventually occur. Will cause an electrical fire accident. Therefore, it is necessary to have a device for detecting the residual current (also known as leakage current or leakage current) in the line, which is used to measure the electrical parts in the electrical insulation between the metal parts, or the live parts and the grounding parts. In the meantime, through the current formed by the surrounding medium or the insulating surface, the early warning of such electrical fires can be realized, and the purpose of eliminating fire hazards can be achieved.
3Electrical fire monitoring system The electric fire monitoring system refers to a system that can issue an alarm signal, a control signal and can indicate the alarm location when the detected parameter in the protected line exceeds the alarm set value. The electrical fire monitoring system is a means of electrical fire prevention. It is a real-time monitoring system that acts before the occurrence of electrical fires. It is responsible for the task, function and technical means of the "automatic fire alarm system" after the fire has occurred. All aspects are different, and the two cannot be confused and replaced.
The "ARCM" electrical fire monitoring system is independently developed and produced by Shanghai Ankerui Electric Co., Ltd., including Acrel-6000 electrical fire monitoring system software and ARCM series electrical fire monitoring detectors. It is a new generation of electrical fire monitoring products applied in the dual fields of civil construction and industrial construction. It has the characteristics of ultra-early, high intelligence, miniaturization, multi-function, high reliability, simple and practical. The device is based on a large amount of valuable experience accumulated over the years by the company's system integration projects in the industrial and civil construction fields at home and abroad. The monitoring equipment is designed and developed by industrial computer, has good reliability, and optimizes the human-computer interaction function, making the whole system easy to install, debug and maintain. The host adopts bus data transmission mode and is equipped with residual current type electric fire monitoring. The detectors form a large-capacity electrical fire monitoring system for real-time monitoring and prevention of early electrical fires in high-rise buildings and various industrial sites.
3.1 Basic Principles of Monitoring System The electrical fire monitoring system integrates monitoring, alarming, control and centralized management. The bus is generally connected to a monitoring detector or monitoring unit to communicate with the host and transmit all data collection information. The host collects the received data, monitors the changes of the three-phase current, residual current, temperature, voltage and other parameters of the detected electrical circuit, and feedbacks the current loop status and other information. When an abnormality occurs in the measured line, the electrical fire monitoring detector collects signals through the tools such as transformers and temperature sensors, and sends an alarm signal when the monitored value exceeds the set threshold and reaches the trigger time, and the alarm signal is uploaded to the monitoring device. In the further identification and judgment, the monitoring host issues a fire alarm signal, the alarm indicator lights up, the alarm sounds with a card, and an alarm message is displayed on the display screen, the alarm position is specified, the on-duty personnel quickly perform the inspection process, and the alarm information is sent to the centralized control. At the same time, the duty personnel can also control the equipment to cut off the faulty loop power through the monitoring equipment, and link other fire-fighting equipment to prevent the occurrence of electrical fires.
3.2 The basic components of the monitoring system The electrical fire monitoring system (GB14287) gives the definition and basic components of the electrical fire monitoring system. The electric fire monitoring system is a system that can issue an alarm signal, a control signal and can indicate an alarm part when the detected parameter in the protected line exceeds the alarm set value, and is composed of an electrical fire monitoring device and an electrical fire monitoring detector.
The electrical fire monitoring system developed by Shanghai Anke Rui Electric Co., Ltd. mainly includes: Acrel6000 electrical fire monitoring equipment and ARCM series electrical fire monitoring detectors. Depending on the size of the project, different system solutions are available to achieve better and better goals. Generally we are divided into: small single building; large single building; large group building. The basic system structure diagram for each type of project is given.
System topology
3.3 Basic functions and features The Acrel-6000 electrical fire monitoring system is used to receive field devices such as residual current electrical fire detectors to achieve alarm, monitoring, control and management of protected electrical circuits. Hardware/software system. It mainly includes the following six functions: monitoring alarm; fault alarm; control output; self-test; alarm record; The monitoring alarm function mainly includes: real-time status of the monitored loop switch; fault signal indication; linkage input; monitoring alarm response time of ≤30s; monitoring alarm sound signal indication and operation. The fault alarm function includes: connection line disconnection between the monitoring device and the detector, short circuit fault monitoring; monitoring equipment main power supply undervoltage (≤80% main power supply voltage) or overvoltage (≥110% main power supply voltage) monitoring. The control output function includes: remote control operation for opening or closing of individual or all monitored units; alarm control output; trip control output. Self-test functions include: open circuit and short circuit check of communication lines; manual check or system self-test. The alarm recording function includes: alarm, fault event type, occurrence time record; query according to the record date, fault type and other conditions; alarm record query and print function. Operational grading includes: daily duty personnel, can enter the software interface to view real-time monitoring situation, eliminate alarm sounds and query alarm records; monitor operators, can operate other operations except for information maintenance of the system itself; system administrators, operating systems Any of the functional modules.
In addition, the ARCM series of electrical fire monitoring detectors that are compatible with electrical fire monitoring equipment are responsible for uploading the parameters of the monitored line. The monitoring detector mainly separates the voltage signal, the current signal and the residual current signal through the transformer, enters the electric parameter acquisition module, uploads the sampled and calculated data to the MCU processing unit, and the MCU processing unit further processes the received data. And collect the temperature signal of the temperature detection module, compare the data with the previously set protection parameters after processing, determine whether there is a fault, and display the data in real time on the LCD or LED display. If a fault occurs, it will be processed according to the previous set fault handling mode to protect the power supply safety, and trigger the sound and light alarm to notify the staff, and store the fault type, time and parameters in the memory chip. In addition, the MCU processing unit also receives the fire linkage and smoke linkage signals from the linkage input module, cooperates with the fire protection system, and remotely cuts off the power supply to prevent fire. The MCU processing unit can exchange data with two upper computer systems through the dual communication module, which facilitates the monitoring of the device by the upper computer, and ensures that the two systems do not affect each other, and at the same time reduces the system investment cost, facilitates later maintenance, and facilitates the electrical fire system. Popularity. 4 Precautions 4.1 Applicable to electrical fire monitoring system Distribution system protection grounding form 1) Distribution system grounding form TN system definition: The power system has a little grounding, the exposed conductor of the electrical device is connected to the location through the protection line .
The TN system can be divided into: TN-S system, the neutral line (N line) and the protection line (PE line) of the whole system are separated; in the TN-C system, the neutral line and the protection line of the whole system are unified. In the TN-CS system, a part of the neutral and protection lines in the system are unified.
Definition of TT system: There is a point in the power system that is directly grounded. The exposed conductive part of the electrical device is independent of the power system grounding point through the protective grounding wire.
2) Problems that should be paid attention to in different grounding systems. When installing residual current type electric fire monitoring detectors, N lines and PE lines must be strictly distinguished. Three-wire four-wire or four-pole four-wire type N lines should be connected to residual current mutual inductance. Device. The N wire through the transformer shall not be used as a PE wire. It shall not be grounded repeatedly or the device may be exposed to the conductor.
In the TN system, the TN-C system must be retrofitted to TN-CS, TN-S system or partial TT system before the residual current type electrical fire monitoring detector can be installed. In the TN-CS system, the monitoring detector is only allowed to use a separate part of the N line from the PE line.
4.2 Installation of residual current transformer 1) Residual current transformer threading residual current transformer should distinguish the phase line, N line and PE line in the power grid before threading. The phase line and the N line must pass through the residual current transformer together, and the PE line cannot pass through the transformer. In the system, if the N line does not pass through the transformer together with the phase line, once the three-phase load is unbalanced, a current will flow through the N line, and the detector detects the current signal, that is, a malfunction occurs. The N lines between different circuits are not connected or grounded repeatedly. Otherwise, it will cause malfunction. When the system is running, the leakage current value is too large and an alarm occurs. A large part is caused by such a situation. If the PE line passes through the transformer together with the N line and the phase line, it will also cause the rejection or malfunction of the monitoring detector.
Not all residual current monitoring needs to penetrate the phase line into the transformer. The total residual current monitoring method of the TN-S system can be excluded. It can pass only one cable through the residual current transformer. The advantage of this method is that a small residual current transformer can be used to improve the measurement accuracy; in the later stage, if the transformer fails, the maintenance is convenient. The specific wiring diagram is as follows.
TN-S system total residual current wiring method
2) Installation position of residual current transformer The residual current transformer should be installed in a place convenient for maintenance, and should be kept away from strong magnetic fields. There is no problem with the installation of the transformer. The transformer can be hung directly on the cable or fixed in the distribution box.
The residual current transformer installation and the upper or lower end of the switch breaker do not affect the monitoring of the protected line. However, in order to facilitate maintenance in the future, it is better to install at the lower port of the switch. It is not necessary to power off the upper switch during power failure maintenance, and only need to disconnect the switch at this level to repair.
4.3 Parameter setting of the electrical fire monitoring detector The determination of the operating current value is often determined according to the value of the normal leakage current of the load after the field loop. Actual situation In the power system, the normal leakage current of different circuits is different, and the rated residual current non-action value should be not less than twice the maximum leakage current of the protected electrical circuit and equipment during normal operation. The leakage current value of the protected electrical circuit during normal operation should be controlled to less than 500 mA. If the leakage current is greater than 500 mA, the monitoring detector should be set in the next-level power supply circuit, or the line or equipment should be inspected or replaced. For the protected line as the power line, in order to avoid the large-scale equipment starting instantaneous ground leakage current caused by the device alarm action, the monitoring detector's action time should be extended to avoid the abnormal leakage when the device starts, to prevent malfunction.
Hierarchical protection application principles. System applications often have hierarchical protection, common 2 to 3 levels, the selection principle of the upper and lower levels: in terms of operating current, the setting of the upper device must be at least twice that of the lower device; in terms of the trip time, the delay time of the upper device should be greater than The operating time of the primary residual current protection device, and the difference of the action time shall not be less than 0.2s.
Residual current electrical fire monitoring detectors are generally not used alone, but are used in conjunction with electrical fire monitoring equipment. When a leakage fault occurs, there is no immediate fire. If the power supply of the protected object is automatically cut off when the monitoring detector is protected, it may cause other unpredictable hazards. Therefore, the residual current type electrical fire monitoring detector should be used for alarms, and it is not appropriate to automatically cut off the power. When there is an electrical fire monitoring device, the fault information is reported to the host device, and the attendant confirms the fault information and performs the next operation according to the actual situation.
4.4 Leakage fault check Residual current type electric fire monitoring detectors are generally installed at the outlet end of the power system distribution cabinet (transformation station) or the floor distribution box incoming line. When a fault occurs in a protected line or equipment, the point or location of the specific fault cannot be determined. It is also a cumbersome task to check each line and equipment after the installation point one by one.
First, the cause of the leakage fault is caused by improper wiring or wiring errors, or equipment or line failure or new load. In the new operation project, many cases are caused by improper wiring or wiring errors. At this time, the wiring of the protection circuit needs to be corrected one by one. After the equipment in the protected line is in normal operation, if the residual current value is within the expected range, it can be basically determined that the line is normal. The residual current caused by wiring errors tends to be large.
Secondly, the specific parts of the leakage are detected by means of meter detection method, separate power-off method (one by one elimination method), and power failure measurement method. One of the most effective and convenient methods is the separate power-off method, which can narrow down the fault location one by one and finally find the cause of the fault. In the case that power outages are not allowed, we generally use observation methods and meter measurements. Observing method is mainly to observe whether there is obvious wiring error or arcing phenomenon in the line; in the instrument detection method, we need to have a special hand-held leakage detecting device to detect the size of leakage in each circuit and locate according to the size.
5 Conclusion With the development of China's economy and society, electrical safety has attracted more and more attention, and people have gradually realized that electrical fire monitoring systems play an important role in preventing the occurrence of electrical fires in the early stage. Early countries introduced relevant technical standards to regulate the design and construction of electrical fire monitoring systems, which led to the current chaos in the industry and the system's effects did not achieve the intended purpose. At present, these products have been confirmed to be included in the second batch of fire-fighting products that implement compulsory product certification. They will be included in the national CCC-certified products from January 1, 2013. This shows that the relevant national departments can regulate the quality of such products and market confidence. .
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