This paper briefly describes the composition principle of the electrical fire monitoring system, and analyzes the design basis and related specifications of the electrical fire monitoring system in the application. Finally, through the introduction of the Ankerui residual current electric fire monitoring system in the Haining Leather City Phase V project, the realization of the function of the electrical fire monitoring system and its significance are expounded.
Yang Junjun An Kerui Electric Co., Ltd. Shanghai Jiading
0 Preface
Electrical fire generally refers to the thermal energy that is discharged due to faulty electrical lines, electrical equipment and power supply and distribution equipment, such as high temperature, arc, electric spark and non-faulty energy; for example, the hot surface of electric heating equipment, with combustion conditions Fires caused by ignition of the body or other combustibles, including fires caused by lightning and static electricity. Electrical fires mainly include the following four aspects: electric leakage fire, short-circuit fire, overload fire, and excessive contact resistance.
The "China Fire Statistical Yearbook" of the Fire Department of the Ministry of Public Security shows that among the fire accidents in 2010, electrical fires ranked first, and the proportion of them was on the rise, causing heavy losses. In fact, electrical fires have become the main cause of fire safety, not only in many times, but also in large losses, and have remained high for many years.
The proportion of electrical fire accidents has increased year by year, which is worrying. For the severe electrical fire situation, early prediction, early warning, and forecasting have become the top priority of fire protection work, and the occurrence of electrical fires at the source has become the focus of attention. The task of preventing and effectively curbing electrical fires is imminent. Relevant national departments have successively formulated or revised relevant standards and regulations, and required to set up an electrical fire monitoring and alarm system in the building.
1 reference standard
In recent years, in order to increase the intensity of electrical fire monitoring and prevention, the state has successively formulated or revised a number of relevant standards and regulations to strengthen the prevention of electrical fires. There are:
(1). It is GB50045-95 (2005 edition) "Code for Fire Protection Design of High-rise Civil Buildings", which stipulates in Article 9.5.1 that it is necessary to install a leakage fire alarm system in places with high fire risk and dense personnel in high-rise buildings.
(2). It is GB50016-2006 "Code for Fire Protection of Building Design", which is stipulated in Article 11.2.7: The following places should be equipped with residual current action electrical fire monitoring system. These venues include various types of theaters, galleries, warehouses, residential communities, hospitals, shops, schools, and more.
(3). The relevant provisions of the national standard "Building electrical fire prevention requirements and testing methods" also clearly require that "the residual current action protector that automatically cuts off the power or alarm should be set at the power incoming end".
(4). The products of the electrical fire monitoring system shall meet: GB14287.1-2005 "Electrical Fire Monitoring Equipment", GB14287.2-2005 "Residual Current Electric Fire Monitoring Detector", GB14287.3-2005 "Measurement Temperature Electric Fire Monitoring and Detection" 》
(5). The installation and operation of the electrical fire monitoring system shall meet the requirements of GB13955-2005 "Installation and operation of residual current action protection device"
(6). The power supply of the electrical fire monitoring system shall meet the requirements of GB50052 "Design Specifications for Power Supply and Distribution Systems"
(7). The design of the electrical fire monitoring system shall meet the requirements of the Design Method of Electrical Fire Monitoring System (Interim Provisions)
2 system components
According to the national standard GB14287-2005 "Electrical fire monitoring system" and related specifications "Electrical fire monitoring system design method" (interim regulations), the basic components of the electrical fire monitoring system should include: electrical fire monitoring equipment, residual current electrical fire It consists of three basic product categories: monitoring detectors and temperature-measuring electrical fire monitoring detectors.
(1) The residual current type electrical fire monitoring detector is composed of a monitoring detector and a residual current transformer (two pairs of plug-in type and closed type); the temperature-measuring type electrical fire monitoring detector is composed of a monitoring detector and a tester. The temperature sensor is composed of.
(2) The residual current type electrical fire monitoring system adopts a layered distributed structure, which is composed of station control management layer, network communication layer and field device layer. Each electrical fire monitoring detector accesses the communication server through the shielded twisted pair RS485 interface, adopts the MODBUS communication protocol bus type connection, and then enters the industrial switch through the Category 5 TCP/TP protocol, and then reaches the monitoring host through the optical cable.
a) The field device layer is mainly used to connect various types of instruments and protection devices for electrical parameter acquisition and measurement in the network, and is also a necessary basic component for constructing the monitoring system. Not only shoulders the burden of collecting data, but also the terminal component that executes background control commands.
b) The communication control layer is mainly composed of a communication server, an interface conversion device, and a bus network. This layer is a bridge for data information exchange. Different interface conversion devices provide various interfaces such as RS232, RS422, RS485, SPABUS, etc., and Ethernet. The networking mode is flexible, supporting peer-to-peer communication, fieldbus network, Ethernet, etc. Configuration network. The communication server is mainly used to directly transfer various control commands of the host computer to the on-site instrument and meter, and is responsible for collecting, classifying and storing the data information returned by the field instrument, such as voltage/current and other electrical parameters and input switch state. Modify the internal parameters of the instrument or various operation commands for controlling the opening/closing of the relay; the microcomputer protection device is mainly to ensure the normal operation of the upper computer and avoid the interference or damage caused by the unstable signal in the network; the interface conversion device This is because there is a difference in the communication interface between the field instrument or other series of devices and the host computer, and conversion is required to exchange data.
c) Management The measurement and control layer is for the management of the monitoring network, which is directly facing the user. This layer is also the uppermost part of the system, mainly consisting of electrical fire monitoring system software and necessary hardware equipment such as computers, printers, UPS, etc. The software part has a good human-computer interaction interface, and reads various kinds of data information collected by the front-end machine through the data transmission protocol, and automatically performs calculation and processing, and reflects the operation state of the scene by means of graphics, digital display, sound, etc., and Accept the operation command of the manager, send and detect the execution status of the operation in real time to ensure the normal operation of the power supply unit.
3 system characteristics and working principle
The characteristic of the electrical fire monitoring system is that the residual current electrical monitoring is an advanced pre-alarm system. Unlike the traditional automatic fire alarm system, the early warning of the electrical fire monitoring system is to avoid losses, while the traditional automatic fire alarm system is to reduce losses. Therefore, this means that whether it is a new or rebuilt project, especially the unit that has installed the automatic fire alarm system, the root cause of the electrical fire monitoring system still needs to be installed.
The electrical fire monitoring system measures two physical quantities of residual current and temperature.
The residual current measurement is based on Kirchhoff's current law: at the same time, the sum of the current vectors flowing into and out of a node in the circuit is zero. Taking the TN-S system as an example, A/B/C/N is simultaneously passed through the residual current transformer. When there is no leakage in the system, the current vector sum of the residual current transformer flowing into and out is zero. At this time, the residual current The secondary current induced by the transformer is also 0; when a relatively large earth leakage occurs, the current vector sum of the current transformer flowing into and out of the residual current is no longer zero, and its magnitude is equal to the current flowing from the earth, that is, the leakage current. The leakage signal is transmitted to the electrical fire detector through the secondary wiring of the residual current transformer, and is sent to the CPU after operation amplification, A/D conversion, and after a series of algorithms, the amplitude of the change is analyzed and judged, and The alarm set value is compared. If the set value is exceeded, an audible and visual alarm signal is sent and sent to the background electrical fire monitoring device.
The temperature measurement uses a temperature sensor, which is generally measured using a Pt100 sensor. This type of temperature sensor is stable in temperature measurement and has a wide measuring range. It is suitable for monitoring cable temperature and ambient temperature in the field. When the temperature changes, the resistance value of Pt100 changes in the same proportion. The resistance signal is transmitted to the electrical fire detector. After a series of signal conversion and calculation, the final result is compared with the temperature alarm setting. If the value exceeds the fixed value. An audible and visual alarm signal is sent and sent to the background electrical fire monitoring device.
4 System design considerations and methods
4.1 Electrical fire monitoring system mainly monitors two types of objects, residual current and temperature, and should pay attention to the basic points in design.
(1) About residual current
Since the principle of residual current monitoring uses Kirchhoff's current law, there are certain requirements for the form of the low-voltage power distribution system to be applied. At present, low-voltage power distribution systems that can apply residual current transformers are: TT system, IT system, TN-S system, and cannot be used in TN-C system. For users who will design and install an electrical fire monitoring system, whether it is a new project or an old engineering project, first check the system grounding form of the user's low-voltage power distribution system. Otherwise, design and install the residual current transformer. Detection is simply not possible.
Regarding the AC220V single-phase power supply system, the residual current transformer only needs to cover the L/N power lines, but the neutral line N is not allowed to be grounded again. For the AC380V three-phase power supply system, due to the three-phase three-wire system, three-phase four-wire system, three-phase five-wire system, etc., the residual current transformer is simultaneously sheathed to the A/B/C three-phase power line according to the specific situation. Or cover the A/B/C/N line at the same time. Similarly, the neutral line N is not allowed to be grounded again, and the protection line PE must not pass through the transformer.
When the system grounding type is TN-C type, the industrial automation network must be converted into a TN-S type, TN-CS type or partial TT type system before the residual current detecting device can be installed.
(2) About temperature
Temperature measurement has nothing to do with the form of system grounding. It mainly considers the temperature of key parts of low-voltage power distribution equipment including cables, and is generally applied in secondary protection lines. The temperature probe Pt100 can adopt the contact arrangement method. When the object to be detected is an insulator, the temperature sensor of the detector should be directly disposed on the surface of the object to be detected. When the object to be tested is the temperature change inside the power distribution cabinet, a non-contact arrangement can be adopted, which is close to the heat generating component.
4.2 Point allocation in system design
According to the national standard GB13955-2005 "Residual current action protection device installation and operation" in the provisions of 4.4 on the classification protection, when installing the residual current fire monitoring device, the steps of the point allocation principle are:
(1) Study and analyze the relevant drawings of the controlled low-voltage AC380V/220V distribution line, investigate and verify the distribution of building electrical, and determine the location of power distribution equipment (such as power distribution cabinets, boxes, disks, cables, etc.). Each monitoring detector is assigned to the corresponding power distribution equipment to determine the number of detectors and avoid resetting waste.
(2) Determine the hierarchical protection. In order to reduce the range of power failure caused by the occurrence of personal electric shock accidents and ground faults, three-stage (or two-stage) residual current protection devices of different capacities are usually installed at different locations of the power supply line to form hierarchical protection. According to the power load and line conditions, it is generally divided into two or three levels of protection, suitable for urban and rural first and second level protection.
Among them, important routes should include security, fire, emergency power, channel lighting and important places that do not allow power outages.
(3) In the secondary protection, all the switches shall be equipped with a residual current fire monitoring detector, that is, at the power supply end of the line (first level protection) and the branch head end (second stage also called end protection). Install the residual current detector and connect it to the electrical fire monitoring system for fire monitoring and alarming purposes only.
(4) In the third-level protection, the residual current detector and the action protection device shall be installed at the third-level (ie, end protection) switch, but the electrical fire monitoring system shall not be connected in order to prevent personal electric shock.
(5) Temperature detection is based on the basic principle that heat is generated when the power distribution equipment is abnormal.
1 Transformer low-voltage side outlet terminal, transformer body temperature (wind temperature, oil temperature, water temperature) test point, load switch contact.
2 Incoming and outgoing busbar contacts, automatic switch (circuit breaker, knife switch) contacts, large current conductor concentrated parts, and cable docking points of each power distribution cabinet (box).
3 female joint cabinet main contact, knife switch contacts.
4 compensation capacitor terminal, transfer switch contacts.
5 According to the total number of points installed, select the corresponding wall mount, vertical or piano.
5 System parameter configuration
5.1 Alarm value setting range
According to the national standard GB14287.2-2005, the alarm value of the residual current type electrical fire monitoring detector is set between 20~1000mA. According to this requirement, the residual current action value at the power supply main line is generally set to 400~800mA, and the residual current action value on the power branch line is set to 100~400mA. Generally, the residual current type electrical fire monitoring detection is set at the actual site. The alarm value of the device shall not be less than 2 times the maximum value of the leakage current during normal operation of the protected electrical circuit and equipment, and not more than 1000 mA. The alarm setting value of the electrical fire detector should take into account the normal leakage current of the power distribution system and the electrical equipment.
5.2 Refer to the cable temperature rise alarm setting reference, according to the "Power Cable Design Specification" for cable temperature requirements
(1) High temperature places above 60 °C should be selected according to the requirements of high temperature, duration and insulation type. Heat-resistant PVC, XLPE or Ethylene-propylene rubber insulation and other heat-resistant cables should be used. Insulated cable. It is not advisable to use ordinary PVC insulated cables in high temperature places.
(2) The ambient temperature of the cable's continuous allowable current carrying capacity shall be determined according to the multi-year average of the meteorological temperature of the area of ​​use and shall comply with the regulations. When the indoor cable trench is laid, the ambient temperature is the average daily maximum temperature of the hottest month of the site plus 5 °C.
(3) The temperature rise of the cable is related to the laying and heat dissipation conditions.
6 system design examples
The fifth phase of Haining Leather City project is located on the north side of Haizhou Road, on the east side of Guangshun Road, on the west side of Shaying Port, across the road from Haining China Leather City Phase I and Phase II, and Haining China Leather City Phase IV Mink The square plot is connected. The total land area of ​​the project is 56,906 square meters and the total construction area is about 182,300 square meters. It consists of two 26-storey hotel apartments and a 7-storey commercial center. The hotel apartment and commercial center are interconnected by the corridor, and the project design and The management has absorbed the international advanced concept, and based on the successful experience of Haining China Leather City 234, relying on Haining's booming leather industry advantage, leather city management advantage, customer source advantage, radiation advantage, and popularity, it gradually cultivates It has become a large-scale professional market with batches and zeros, which is dominated by suede, leather garments and luggage as the leading products in East China and even the whole country. The operation mode of the market is mainly in the form of a large-scale living museum, which is also a one-stop sales of various leather fur products of a single brand.
Haining Leather City Phase 5 electrical fire monitoring system consists of electrical fire monitoring device Acrel-6000/B, leakage fire detector ARCM200-J4, and leakage current transformer AKH-0.66L.
The Acrel-6000 electrical fire monitoring system is an industrial grade that is independently developed by the company 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. The system is applied to the fire control center of large shopping malls, living quarters, production bases, office buildings, shopping malls and other areas, and telemetry, remote adjustment, remote control and remote signaling of detectors scattered in the building are convenient for monitoring and management. The system uses a standard Modbus field bus to connect detectors with communication functions. When the detected parameter in the field protection circuit exceeds the alarm set value, it can send out alarm signals and control signals, can indicate the alarm part and save the alarm. information.
In the fifth phase of Haining Leather City, there were 36 ARCM200-J4 residual current fire detectors installed in the switchgear of the substation. The on-site fire detector is connected to the Acrel-6000/B wall-mounted electrical fire monitoring system of the control center by bus. The system has the advantages of convenient installation and transportation, high cost performance and convenient maintenance.
The main technical parameters
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1. Power supply:
1 rated working voltage AC220V (-15% ~ +10%)
2 Backup power supply: When the main power supply is under voltage or power failure, maintain the monitoring equipment working time ≥ 4 hours Hardware Business Network Information Center) http://news.chinawj.com.cn
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