Xu Shuang Ankerui Electric Co., Ltd. Shanghai Jiading 201801 1 Prevention and control of electrical fires With the development of science and technology, the progress of human society, and the accelerating process of urbanization in China, the production and use of electrical energy has been increasing year by year and has become the most important energy source. With the gradual deepening of people’s understanding of safe electricity and electricity, the number of fire accidents caused by electrical faults has increased due to personal injury accidents caused by non-standard power consumption decreasing year by year, and vicious fire accidents involving heavy fires and group deaths and injuries. From time to time, this contrasts sharply with the trend of China's total number of fires decreasing year by year. According to statistics from authoritative departments, a total of 675,000 fires were reported by the national fire department from 2008 to 2012. Of the approximately 623,000 fires identified, the number of electrical fires was approximately 208,000, accounting for 33.37%. For example, the occurrence of electrical fires such as the commercial buildings in Jilin City in 2010, Xinawan Hotel in Changsha City in 2011, Jiugong Town in Daxing District in Beijing City in 2012 and the Ryde Commercial Building in 2012 in Tianjing County brought about the life and property safety of the people. Serious threats. In the face of such a severe electrical fire situation, how to eliminate fire hazards as early as possible and minimize and reduce the occurrence of electrical fires have become the focus, difficulty, and social focus of fire prevention work in the fire protection industry. 2 Analysis of the Causes of Electrical Fires Electrical fires are mainly caused by electrical faults such as short circuit, over-current, poor contact, and electrical leakage in electrical lines or equipment. Electrical faults that cause electrical fires are categorized from their manifestations: sudden faults and gradual faults. Mutant faults are also called metal short-circuit faults; electrical faults such as over-current, poor contact, and electrical leakage are generally characterized as gradual failures, gradual failures are not eliminated in time, and eventually they will evolve into abrupt failures. After a gradual failure occurs, it will develop to an abrupt failure in an irreversible situation. In this process, it will directly appear as an abnormal release of electric energy, ie, an increase in leakage current, an increase in the temperature at the terminal, etc., and the generation of a fault arc. These factors will eventually lead to an increase in the temperature at the point of failure. In particular, the high temperature of thousands of degrees Celsius generated by a fault arc can ignite the surrounding combustibles and cause fire. 3 Electrical fire monitoring system Electrical fire monitoring system refers to the system that can send out alarm signals, control signals and can indicate the alarm location when the detected parameters in the protected circuit exceed the alarm setting value. The electrical fire monitoring system is a means of electrical fire prevention, a real-time monitoring system before the occurrence of electrical fires, and an “automatic fire alarm system†after the occurrence of a fire. It assumes the tasks, functions, and technical measures taken. All other aspects are different, and the two cannot be confused and replaced. The "ARCM" electrical fire monitoring system is independently developed and produced by Ancorui Electric Co., Ltd. It consists of 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 buildings and industrial buildings. It has the characteristics of ultra-early, high intelligence, miniaturization, multi-function, high reliability, simple and practical. The device was developed based on the many valuable experiences accumulated by the company in the system integration projects in the domestic and foreign industrial fields and civil construction fields for many years. The monitoring equipment adopts an industrial computer for design and development, which has good reliability, and at the same time optimizes the human-computer interaction function, so that the entire system is easy to install, debug and maintain. The host adopts a bus-based data transmission method, and the residual current-based electrical fire monitoring is matched. The detector, which constitutes a large-capacity electrical fire monitoring system, is suitable for real-time monitoring and prevention of early electrical fires in high-rise buildings and various industrial sites. 3.1 The basic composition and working principle of the system 1) Basic composition Acrel-6000 electrical fire monitoring system adopts layered distribution and open structure design and consists of station management layer, network communication layer and field device layer. All electrical fire monitoring probes are connected to the communication server through a shielded twisted pair RS485 interface, using a MODBUS communication protocol bus type connection, and then enter the industrial switch through the Category 5 TCP/TP protocol, and then reach the monitoring host through the optical cable. a) The field device layer is mainly connected to various types of instruments and protective devices used for the collection and measurement of electrical parameters in the network, and it is also a necessary basic element for constructing the monitoring system. The monitoring equipment can receive the alarm signal from the electrical fire monitoring detector, issue the sound and light alarm signal and control signal, indicate the alarm location, and record and save the alarm information. It is the management center of the system. It not only shoulders the burden of collecting data, but it is also a terminal component that executes background control commands. The monitoring equipment has the functions of automatic switching between main and standby power to ensure the stability of the system. b) The communication control layer is mainly composed of communication server, interface conversion device and bus network. This layer is the bridge for data information exchange. Different interface conversion devices provide various interfaces such as RS485 and Ethernet, flexible networking methods, and support for peer-to-peer communication, fieldbus networks, Ethernet, and other types of configuration networks. The communication server is mainly used to directly transmit various control commands of the host computer to the field instrument and meter, and is responsible for collecting, classifying, and storing the data information sent back by the field instrument, such as voltage/current and other electrical parameters and input switch status. , Modify the internal parameters of the instrument or various control relays open / close operation commands. c) Management The monitoring and control layer is for the management personnel of the monitoring network, and this layer directly faces the users. This layer is also the uppermost part of the system, mainly by the electrical fire monitoring system software and necessary hardware equipment such as computers, printers, UPS and so on. The software part has a good human-computer interaction interface. It reads the various data information collected by the front-end machine through the data transmission protocol, and is automatically calculated and processed to reflect the operating status of the site by means of graphics, digital display, and sound. Accept the operation command of the management personnel, send and check the execution status of the operation in real time to ensure the normal operation of the power supply unit. 2) Working principle The basic principle is that when the current, temperature and other parameters in the electrical equipment are abnormal or abrupt, the terminal probe (such as the residual current transformer, temperature sensor, etc.) uses the electromagnetic field induction principle and the temperature effect to collect the information. And sent to the monitoring probe, after amplification, A / D conversion, CPU analysis and judgment of the change in amplitude, and compared with the alarm set value, once the set value is exceeded, then send an alarm signal, but also to the The monitoring equipment is further identified and determined by the monitoring equipment. When it is confirmed that a fire may occur, the monitoring host issues a fire alarm signal, turns on the alarm indicator, sounds the alarm, and displays the fire alarm and other information on the LCD. The on-duty personnel quickly checks and handles the accident scene according to the above information, and sends the alarm information to the centralized console. 3.2 System Design and Typical Networking Schemes a) Large-scale construction group network plan Large buildings, high floors, multiple buildings scattered. Acrel-6000/Q electrical fire monitoring equipment +ACREL6000/B electrical fire monitoring equipment + electrical fire monitoring detector three-tier structure networking mode, to facilitate regional management, using RS-485 network communication, Ethernet communication, Ethernet communication To meet the high real-time communication requirements. b) Large-scale single-unit construction network plan Large-scale single-unit buildings adopt Acrel-6000/Q electrical fire monitoring equipment + electrical fire monitoring detectors to build a two-tier networking mode with comprehensive detection and management functions and high cost performance. The RS-485 network is adopted, and the communication medium adopts shielded twisted pair cables. Meet the high real-time communication requirements. c) Medium-sized construction network plan The medium-sized single building adopts Acrel-6000/B electrical fire monitoring equipment + electrical fire monitoring detector two-tier structure networking mode, cost-effective, cost-effective, using RS-485 network, to meet the high real-time communication requirements. d) Small building electrical fire monitoring system Small buildings, using Acrel-6000/B electrical fire monitoring equipment for monitoring, cost-effective, cost-effective. 4 Reasonably set up an electrical fire monitoring system to effectively prevent electrical fires The results of engineering practice show that the reasonable application of electrical fire monitoring system reduces the occurrence of electrical fire to a certain extent, but there are still some misunderstandings in the engineering application of electrical fire monitoring systems. 4.1 Avoiding Expansion of Residual Current Monitoring Detector Function Through the analysis of the causes of electrical fires, we can see that the proportion of electrical fires caused by electrical leakage is not very high, and engineering practice shows that the leakage of new electrical systems is mainly due to the insufficient dielectric strength of electrical equipment. The insulation performance of the selected wire and cable is not up to standard, or the construction of the electric circuit is incorrect or irregular. Therefore, setting up a residual current type electric fire monitoring detector in the project can, to a large extent, find problems in the process of handling the electric system facilities. . It is reasonable to say that the electrical fire gas monitoring system has been controlled and operated normally, and the problems existing in the construction of the electrical system have basically been solved, and some fire hazards have also been eliminated. However, as far as the current level and current status of the electrical system in China are concerned, These problems are often difficult to solve effectively in a short time, so it is necessary to set up a residual current type electric fire monitoring detector from the perspective of ensuring the construction quality of the electrical system. Therefore, it is suggested that in the new construction project, the principle of setting the first stage of the low-voltage distribution system should be used to minimize the number of residual current-type electrical fire monitoring detectors. At the same time, it will mainly focus on how to ensure that the dielectric strength of selected electrical equipment is increased, thereby fundamentally eliminating the potential for such electrical fires. Through the analysis of electrical fire accidents, electrical fires caused by electrical leakage are often found in old buildings that have been used for many years. With the increase in the number of years of use, the insulation performance of electrical wires and cables used in buildings has decreased, and the chance of electrical leakage causing fires has greatly increased. Such a building can appropriately increase the number of residual current electrical fire monitoring detectors, thereby effectively monitoring the electrical system for leakage faults. 4.2 should strengthen the engineering application of arc type electric fire monitoring detector Through the analysis of the causes of the fire in the final fire, it can be seen that, regardless of the type of fire caused by an electrical fault, it is ultimately caused by the energy generated by the arc of an electrical device or circuit that ignites the surrounding combustibles. Therefore, in order to effectively reduce the occurrence of electrical fire, the most effective means is the effective application of arc-type electrical fire monitoring detectors. However, due to the technical difficulty in identifying fault arcs, there is currently no mature product in China. It is believed that in the near future, with the advancement of technology, the engineering application of this type of product will greatly improve the current status of prevention and control of electrical fire in China. 4.3 The use of electrical fire monitoring system should not affect the normal production and life The electrical fire monitoring system is an independent subsystem of the fire automatic alarm system and belongs to the fire pre-alarm system. That is, the alarm signal of the electrical fire monitoring system merely indicates that there is a potential safety hazard that may trigger an electrical fire, and does not indicate the occurrence of an electrical fire. Therefore, the electrical fire monitoring system should not be the same as the fire automatic alarm system. After confirming the alarm information, the linkage control cuts off the power supply and affects the normal production and life. It should be the warning personnel to check the electrical system in time to eliminate electrical faults. To eliminate fire hazards. 5 Major Metering Functions and Selection Schemes references: [1]Electrical fire monitoring system and electrical fire prevention. Gao Jun. Building electrical, 2013.11 [2] Ankerui Electric Co., Ltd. Product Selection Manual 2013.1. About the Author: Xu Shuang, female, undergraduate, Ankerui Electric Co., Ltd., whose main research direction is the design of electrical fire monitoring and power supply monitoring of fire fighting equipment. Email: Mobile QQ
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