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In recent years, the number of fires has risen continuously, especially electrical fires, accounting for more than 30 % of the total number of fires . The proportion of electrical fires in major and particularly significant fires is as high as 70 %. Domestic fire protection has become a very important and urgent task in China's current fire prevention work.

At present, there are relatively few standards and design specifications for household electrical fire monitoring in the residential sector in China. GB 50096-201l “Design Code for Residential Buildings” also only requires that residual current protection or residual current action alarm should be set on the incoming line of the main power supply of each dwelling. There is no monitoring alarm for each home, and the total number of monitored residential buildings is monitored. The remaining current of the power supply line is far from enough. At present, only the leakage protection switch is installed on the incoming line of households. According to the statistics of the “China Fire Yearbook” issued by the Ministry of Public Security’s Fire Bureau, the actual number of electrical fires caused by the surplus current is not high, and there are short-circuits, overheating, poor contacts, electrical faults, and overloads that account for higher proportions. And there are currently no effective and targeted monitoring tools in the family. JGJ l6 — 2008 { Design Code for Civil Buildings> stipulates that buildings with residual current fire alarms should be installed at the incoming line of the power supply, including residential buildings, apartment buildings, etc.; currents for residual current operation protection devices, circuits for home appliances or outlets For 3O mA , it does not apply to bathroom heaters and their electrical circuits. This standard does not belong to the national enforcement standards. Many families actually have a total earth leakage switch installed at the entrance to the power supply and have not been subdivided into a home appliance circuit or outlet dedicated circuit. Coupled with people’s insufficient attention to household electrical fire monitoring and weak awareness of prevention, the requirements of relevant regulations cannot be implemented and implemented in household electrical fire monitoring. Tragedy of household electrical fires occurs year after year.

1 related product standards and specifications

JEAC 8001 — 1978 Internal Rule ( Japan ) Article 190 Requirements, Building Area 150 m The above-mentioned hotels, restaurants, apartments, collective dormitories, family apartments, public houses, public baths and other places must be equipped with an electrical leakage fire alarm that can automatically alarm. This procedure has played an important role in the control of electrical fires in Japan. Its electrical fires account for only 2 % - 3 % of the total fire ( its electricity consumption per person is 8 times that of China ) .

In 1993 , GB14287-93{ Fire Leakage Current Action Alarms } organized by the Ministry of Public Security Shenyang Fire Research Institute was issued and implemented. After the implementation of the national standard, relevant regulations and standards were not issued simultaneously. In the following ten years, there were not many products entering the market, and promotion and application work was almost stagnant. But ten years it is the rapid rise in China's per capita electricity consumption in the period, an electrical fire from seven in 1978. 8% rise to 30% in 2008, currently has remained at this high level.

In 2005 , GB 14287-2005 “Electrical Fire Monitoring System” and GB13955-2005 “Installation and Operation of Residual Current Operation Protection Device” were introduced. At the same time, GB 50045-2005 { High-rise Civil Building Design Fire Protection Code "partial revision provisions, adding 9th . Five "leakage fire alarm systems". 2005 was an important year for the development of electrical fire standards. At this time, electrical fire monitoring systems tend to be standardized.

In 2008 , the new "Fire Law of the People's Republic of China" was promulgated and implemented. The principle of "prevention-oriented, prevention-disinfection combined" was implemented in firefighting work, and in particular , mandatory regulations for early warning and forecasting of electrical fires were intensified . JGJ 16-2008 {civil electrical design specifications ", DG / TJ 2O48 - 2 () () 8" civil electric fire design procedures ", JGJ 242-2011" residential building electrical design specifications ", GB 50096-20l1" Residential Design specifications, GB 50054-2011 "Low-voltage power distribution design specifications" and other standards and design specifications have been introduced in succession, which has guiding significance in the field of civil building electrical design.

In recent years, GB 50116-2013 "automatic fire alarm system design specifications", GB 50016 - 2014 "building design for fire protection" two important specifications promulgated and implemented. GB l4287 — 2O14 Electrical Fire Monitoring Systems Part I: Electrical Fire Monitoring Equipment, Part II: Ignition - Type Electrical Fire Monitoring Detectors, Part III: Temperature- Based Electrical Fire Monitoring Detectors, Part 4: Fault Arcs Detector launched. The field of electrical fire is further regulated. In the standard system of GB 14287 "Electrical Fire Monitoring System" , there is GB 14287 "Electric Fire Monitoring System" Part 5: Measuring Pyrolysis Particle Type Electrical Fire Monitoring Detector and Part 6: Electric Fire Limiting Current Limiting Protector The standard has not been officially promulgated and implemented In addition, there are static detectors, insulation monitors, and no-arc switch products for electrical fire protection. These products can eventually be applied to homes, and basic application technology research and more economical and stable sensor detection technologies need to be strengthened.

2 home electrical fire monitoring system solutions

Household electrical fire monitoring systems are a subdivision of electrical fire monitoring systems . In the family-specific application environment, the overall requirements of the security control system are easy installation and wiring, simple operation, beautiful appearance, safe and reliable system operation, and strong economy.

2 . 1 Combined Electrical Fire Monitoring Detector ( for Home Applications )

The main function of the traditional leakage switch is to protect personal safety. When the leakage current of the power line exceeds the personal safety value (30 mA) , the power is cut off immediately. It is impossible to ascertain the normal operation of the circuit and the size of the leakage current during the trip. It is impossible to understand the insulation status of the circuit. Changes, unable to make a timely and effective assessment of the current insulation status, can not forecast the electrical fire. There are four main types of electrical fires in a family . One is overload, the other is short circuit, and the third is excessive contact resistance ( poor contact, resulting in ignition and heating ) , and the fourth is electrical leakage. That is, in addition to the leakage, there are three more important reasons. In order to protect the power supply line from electrical leakage, electrical fires still occur frequently and are urgently needed to be solved. The effective method is to scientifically install modular electrical fire monitoring detectors.

The combined type electric fire monitoring detector is mainly composed of one-way residual current monitoring plus one-way temperature monitoring with liquid crystal display, adopting a more compact rail-type or wall-mounted installation structure and independent operation. The residual current transformer adopts a special miniature residual current transformer which is equivalent to the size of a one-way coin. It can monitor the load current, residual current, and temperature value at the incoming line of the household's power supply. If the value exceeds the set value, it will alarm and reserve the external data interface. .

2 . 2 arc fault detector

About the fault arc detector related standards, domestic GB14287 . 4 — 2014 “Electrical Fire Monitoring Systems” Part 4 : Fault arc detectors, JB / T l1685-1 — 20l 3 “ General requirements for arc fault detection devices (AFDD) ” etc. Foreign UI 1699-2011 "Fault Arc Circuit Breaker", IEC 62606 "Arc Fault Detector (AFDD) for Household and Similar Uses ". Due to history and various reasons, fault arc detectors have not been well promoted and applied in China. The family of arc fault detectors can mainly solve the problem of poor contact, fire, and short circuit ignition in the household electricity and electricity equipment, ie, string arcing and arcing. In particular, when a string arc occurs, the distribution range is wide, the temperature point temperature measurement cannot be fully covered, the current is very small, the leakage switch or the residual current monitoring does not work enough, but the small arc generated by the open flame energy can ignite the surrounding combustibles. Therefore, installing a fault arc detector is also a supplement to electrical fire monitoring.

According to the standard requirements, when a detected fault occurs within 14 s and more during a period of 1 S , the detector shall send an alarm signal within 30 s and light the alarm indicator. When a detected fault occurs within 9 seconds of the faulty arc in 1 S , the detector shall not emit sound and light alarm signals and control signals, but may use other methods to prompt. Arc duration of which does not exceed O. A small arc of 42 ms or a current value not exceeding 5 % of the rated current is not counted as an arc. Fault arc characteristics are shown in Figure 1 and Figure 2 .

According to the characteristics of household electricity consumption, the fault arc detector has a liquid crystal display and adopts a more compact rail-mounted or wall-mounted mounting structure and operates independently. Can monitor the arc fault, reach the standard value to alarm, record the number and time of occurrence, and reserve the interface.

2 . 3 Electric fire limiting protection

The professional names of such products are "solid-state circuit breakers", "solid-state switches with short-circuit protection functions" or "solid-state short-circuit protectors", etc., which belong to the power electronics technology field. Its working principle is to achieve the load on and off by changing the conductivity of the semiconductor. It is treated semiconductor transistor (semiconductor), a controllable conductivity, become closer to the conductor (little resistance, 0. 02Q) and the proximity of the insulator (large resistance, 220 kO) in a conductive state.

Figure 1 Invalid Fault Arc Sampling Sample

Figure 2 Effective Fault Arc Sampling Samples

The disconnection of the conventional air switch used in the home is a mechanical movement process. The disconnection of the load is accompanied by the generation of an arc, and the breaking time takes several tens of milliseconds ( typically 30 to 50 1 TIS) . The disconnection of the solid state circuit breaker is based on the carrier motion inside the semiconductor. The speed is fast, no arc is generated, and the breaking time is microseconds. It is several ten thousand times to several hundred thousand times faster than the traditional one. It is caused by a short circuit. When the fault current is far from the peak value of the short-circuit current, the circuit is shut off, and the cut-off value ( setting value of the short-circuit protection current ) can be set as needed, which greatly reduces the energy released during the short-circuit, and at the same time greatly reduces the harmful effects of the short-circuit point. Electric sparks. Because the breaking time of the solid state circuit breaker is very fast and the cutoff value can be set, the short circuit breaking capacity of the solid state circuit breaker is theoretically infinite. The ability of solid state circuit breakers to handle short-circuit faults is not affected by the increased capacity of the main power supply and the reduced length of the transmission line.

The difference between the conventional circuit breaker and the solid state circuit breaker is illustrated by the relationship between the current and time before and after the short circuit fault of FIG. 3 .

Fig. 3 Current and time before and after short-circuit fault

The heat generated by the current flowing through the resistor Q — R £. It can be seen from the relationship between the square of current and the time of Figure 4 that the area enclosed by the curve corresponds to the amount of energy released during the short circuit. It can be clearly seen that the energy difference released by the traditional circuit breaker and the solid state circuit breaker in the short circuit. The ratio of released energy is at least 4,000 times.

Fig. 4 Relationship between current squared and time

After the short-circuit fault occurs, the voltage of the main power supply ( single-phase 220 V , three-phase 380 V ) will drop significantly or even fall to near zero, so the power supply for the internal control circuit of the solid state circuit breaker cannot rely on the main power supply, otherwise the current limiting protection for electrical fire protection The device does not work properly and is at risk of getting out of control. Only the auxiliary power supply that is not related to the main power supply ( bus power supply or battery power supply ) can be used as the power supply for the internal control circuit. This effectively solves the problem of the voltage drop caused by the short circuit fault of the main power supply and the electrical fire limiting current protector after taking the main power supply. Problems that lead to abnormal work have strengthened the practicality of the general situation.

The characteristics of the electrical fire limiting protection device are as follows: the limit of short-circuit current is completed in microseconds, the switching speed is greatly improved, the stability and safety of the system are improved, and the short-circuit fault current can be limited before the short-circuit current is far from the peak value of the short-circuit current. , greatly reduce the probability of continuous arc ignition caused by the short circuit of electrical lines/equipment, avoid flammable surrounding combustibles causing fire accidents, and effectively prevent lightning surges from flooding into household electrical circuits and burn down electrical equipment; accurately control switches Operation time; Acousto-optical alarm, timely reminding operation and maintenance personnel; Centralized monitoring, fault location, rapid display of faulty units; long working life, no limitation on the number of switches, good durability; whole machine adopts epoxy potting process, shockproof , moisture-proof, adapted to harsh environments; no contact, no mechanical moving mechanism and no arc, reducing the failure rate and improving the reliability of power supply.

2 . 4 intelligent fire switch/socket

The durability of switch sockets is getting higher and higher, but power failures occur from time to time. For example, a switch socket can be used to power multiple power devices at the same time, especially high-power induction cookers, air conditioners, etc. The load current is too large, making the power line Accelerated aging, resulting in electrical hazards, especially when the load capacity of the switch socket is exceeded, the temperature rapidly increases and there is an electrical fire risk. Sometimes thunderstorms may occur, and lightning strikes may occur. The switch socket cannot protect itself, and there will be great damage to the electrical appliances. An increasing number of electrical fires and accidents have proven that traditional methods cannot effectively guarantee the safety of electricity use. According to the statistics of the fire department , the air switch did not work in more than 80 % of electrical fires. The intelligent fire switch/socket with over-current protection function overcomes the problem of electrical fire caused by over-selection of air switch and inability to timely trip due to overload. When home improvement, it is necessary to pay attention to the strict separation between the PE and N lines of the grounding protection line , regulate the construction, and ensure that the protective ground PE of the building is reliably connected.

The above electrical fire detection and prevention devices can all have external output interfaces, which can be simultaneously connected to the home fire alarm system. The home alarm system then uploads the data to the remote cloud platform through wireless technology. The alarm can be reported on the device when the detector alarms. The home alarm controller may display, and may also push the alarm information to the user's mobile terminal.

3 Summary

Some new sensor technologies, power electronics and monitoring methods are applied to household electrical fire monitoring to eliminate electrical fires caused by various causes. Prevent early warning of electrical fires and notify property professionals to handle and maintain them in a timely manner. In addition, it is also necessary to raise people’s awareness of electrical fires, attach importance to household electrical fire monitoring, design and construct properly, and use electricity safely to ensure the safety of people’s home electricity.

The information in this article comes from the Internet and was reorganized and edited by China Rescue Equipment Network.

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