Talk about the electrical fire hazards of wood processing enterprises and the application of electrical fire monitoring systems

Abstract: This paper analyzes the characteristics, status quo and common electrical fire hazards of wood processing enterprises, and proposes measures to
eliminate electrical fire hazards.

The end introduces the selection of electrical equipment commonly used by woodworking enterprises and the application scheme and product selection of electrical fire monitoring system in its low-voltage distribution system
.

Keywords: wood processing enterprises; Electrical fires; With the rapid development of China's national economy, the wood processing industry has also developed rapidly, and the comprehensive utilization rate of wood has been continuously improved
.

State-owned, collective, private and foreign-owned timber processing enterprises are increasing
.

Due to the low fire performance of the plant of the general wood processing plant, the raw materials for processing are combustible substances, and the remaining waste is easier to burn
.

Among them, after the fire such as wood chips, the smoldering time is long, and it is not easy to find in time; Some processes use flammable glue, so such enterprises are prone to fire, and once a fire occurs, the loss is huge
.

1 The characteristics of wood processing enterprises wood is combustible substance, low ignition point, generally at 250 °C ~ 300 °C, some wood with open flame ignition, the lower ignition point is 157 °C, spontaneous ignition point is generally about
350 °C.

In the process of wood processing, a large number of sawdust, shavings, wood chips, wood flour, etc.
are produced, these substances are looser than wood, large contact surface with air, and moisture is easy to evaporate, so it is easier to burn
than wood.

In addition, if the wood chips are piled up together, the heat produced by the friction when sawing the wood is not dissipated, or the influence of radiant heat, as well as heat generation, etc.
, prompts the gasification process to accelerate, generates more heat, often makes the temperature in the pile continue to increase, and does not disperse, causing spontaneous combustion
.

Especially in the production of wood-based panels, flammable and flammable rubber materials are also used in large quantities, which correspondingly increases the fire hazard in the production process of wood processing
.

Wood processing, in addition to rubber preparation, paint and other sections belong to Class A production, most of the production process belongs to Class C production, but compared with other Class C production, wood processing fire hazard is greater
.

Therefore, the state attaches special importance to the fire prevention work of wood processing enterprises, and lists such enterprises as (1) fire prevention
.

The design and construction review and acceptance of new wood processing enterprises are very strict, and the safety and fire control work of the wood processing enterprises that have been produced is constantly strictly supervised and inspected to prevent the occurrence
of fire accidents.

However, the fire accidents that occurred in wood processing enterprises continued for many years, causing huge economic losses to the country and enterprises, and the safety of people's lives and property was seriously threatened
.

2 Due to the weak foundation of China's social fire control work, the fire situation has lagged behind the development of economic construction for a long time, and the fire incidence rate is still high
.

According to the 1997 statistics released by Sun Lun, director of the Fire Bureau of the Ministry of Public Security on January 1, 1998, at a press conference held in Beijing, in 1997, there were more than 140,000 fires (excluding forest and grassland fires) across the country, killing 2,722 people, injuring 4,930 people, and directly causing property losses of 1.
54 billion yuan
.

Among them, 88 exceptionally large fires occurred, killing 454 people, injuring 366 people, and directly causing property losses of 360 million yuan
.

Among the main causes of fire, fires caused by illegal use of electricity and random pulling and random wiring account for a large proportion
.

It can be seen that the fire protection work of wood processing enterprises cannot be ignored
.

3 The status quo of wood processing enterprises and common electrical hazards In recent years, with the development of the market economy, the wood processing industry has developed rapidly, and the industry pattern has also undergone great changes
.

It has changed from a situation dominated by large and medium-sized state-owned enterprises to a situation
dominated by foreign-funded enterprises, individual and private enterprises.

At present, due to the greater impact of the market economy, the economic returns of the former state-owned large and medium-sized enterprises have been slipping year after year, some have stopped production and closed their doors, some have leased or transferred production plants and equipment, and some have "caged birds" to engage in the tertiary industry
.

In short, the economic benefits of the enterprise are poor, and it is unable to carry out technical transformation of the old factory building and the old electrical circuit, so that the hidden dangers of electrical fire are prominent
year by year.

In recent years, most of the newly built "three-capital" enterprises are designed by the design department, and have been reviewed and accepted by the fire department, and the fire protection situation is generally relatively good
.

However, in order to expand production, improve efficiency, and reduce costs, full load or even overload production
is often used.

In the production process, the stacking of raw materials, products, finished products and waste materials is also relatively dense, neglecting the management of safety and fire prevention
.

Individual and private enterprises, due to the small amount of funds and small scale, only pay attention to production, do not pay attention to safety and fire prevention
.

From design to production are not formal, production and management personnel have weak awareness of fire safety
.

Such enterprises, the production site is narrow, the plant is simple, the equipment layout is crowded, the electrical circuit is randomly pulled and connected, the electrical components are mutilated and exposed, the products are piled up randomly, dust, wood chips are everywhere, and the fire hazard is very serious
.

The electrical fire hazards in wood processing enterprises are mainly in the following aspects
.

3.
1 The design and construction of electrical circuits and equipment are not standardized, and the design and selection of electrical equipment are not carried out in accordance with the relevant national design fire codes and the design specifications for power installations in explosion and fire hazard environments
.

Or the fire and explosion protection level of the production site is not determined properly, and the equipment is not selected properly
.

For example, the paint plant is an explosion hazard place, and some small manufacturers often use ordinary iron shell switches or rubber cover knife gates, and the insulated wires are laid through plastic pipes, and some even directly use insulated wires to supply electricity
to electrical appliances.

Another example: some manufacturers use protective motors to produce
in places where there is a danger of fire and explosion.

Some small manufacturers even concentrate paint, saws, planers and other equipment in a small factory for production, electrical wiring random connection, and so on
.

The construction was rough and not carried out in accordance with the requirements of the construction
code.

The main ones are: poor quality of the purchased electrical materials, insufficient wire and cable diameter, and broken shares in the middle; The connection of wires, cables and equipment or electrical appliances is not equipped with terminal blocks, and nuts are added after direct winding; When the terminal block is connected, the gasket is not used, and the crimping is not tight; Copper, aluminum conductors are directly connected without treatment; Improper use of wire protection tubes; Protective grounding and zeroing mixing; The number of grounding electrodes is not enough, the grounding resistance is large, and so on
.

The load rate of the original power supply equipment and lines is not accounted for, and the cross-sectional area is not calibrated according to the voltage loss; The laying method of the line is not standardized, and things are
connected.

The selection of electrical control components does not take into account the production environment and fire protection level on site
.

3.
2 In normal production, neglect management, do not pay attention to maintenance and inspection of common electrical hazards are: (1) transformer oil shortage, long-term overload, insulation oil quality decline; (2) The doors and windows are damaged, and small animals such as snakes and rats enter the power distribution room; (3) Replace the fuse with copper wire; (4) Lack of oil in motor bearings, poor connection of terminal blocks, defective terminal box covers; (5) The voltage is low, and the starting torque of the motor is not enough; (6) The sealing of the electronic control cabinet is poor, and the internal ash accumulation and dust accumulation are serious; (7) Line insulation aging, shedding, line head exposed; (8) The line is overloaded and the heat is serious; (9) The contact resistance of the joint increases due to oxidation and corrosion; (10) The line is randomly pulled and connected; (11) Replace the iron shell switch and automatic switch with ordinary bakelite knife gate; (12) The outer cover of the iron shell switch is damaged or often opened; (13) Pull high-power ordinary incandescent lamps in places with serious paint and dust; (14) The stacking of finished products is too high, close to the lighting fixtures; (15) After the bulb in the production area is broken, it is not replaced in time; (16) Screw the incandescent bulb above 200W on the bakelite lamp mouth; (17) Production operators are free to use electric heating appliances such as electric furnaces; (18) The lamp port and junction box switch are damaged; Mutilated, bare joints, etc
.

4 Historical lessons In 1990, a fire ruthlessly burned down the timber workshop of Chengdu Timber Comprehensive Factory, with direct economic losses of nearly two million yuan, and indirect losses are difficult to estimate
.

SuccessThe urban fire brigade investigated and collected evidence at the scene and determined that the fire was caused by electricity
.

The afternoon before the fire, after the operation of the production line 5# sawing machine was completed, he did not open the power knife gate, hurriedly left the workshop
.

At night, the magnetic starter of the equipment is broken down by the insulation, causing a short circuit between phases, and the arc and high-temperature copper fused beads fly from the broken shell gap, igniting the sawdust and dust
of the floor slab.

The fire spread rapidly, and in just a few tens of minutes, the timber workshop with a construction area of more than 2,000 square meters and an annual output of 30,000 cubic meters of sawn timber was destroyed
.

The losses are heavy and the lessons are very profound, so it is very important
to improve fire awareness and strengthen safe electricity management.

5 Wood processing enterprises to eliminate the hidden dangers of electrical fire 5.
1 vigorously publicize the "Fire Protection Law", improve fire awareness, increase fire knowledge In recent years, China's fire situation is grim, and large fires occur from time to time, causing a large number of casualties and direct property losses of billions of yuan
.

To a certain extent, it has affected economic construction and social stability
.

The Chinese government attaches great importance to this, and promulgated the Fire Protection Law of the People's Republic of China on April 29, 1998 and officially implemented
it on September 1, 1998.

To prevent fire before it happens, it is first necessary to fully understand the hazards of fire, increase publicity, so that every employee of the enterprise can have a full understanding
of the hazard of fire.

At the same time, it is necessary to strengthen the fire control knowledge and fire skills training of the staff team, and improve the fire prevention and fire fighting ability
of every worker.

5.
2 Conscientiously implement the "Fire Protection Law" according to the specifications of design, construction, acceptance, prevention of fire hazards and the generation of hidden dangers of fire, for new and technical transformation of wood processing enterprises, must be in strict accordance with the relevant building fire code and "explosion and fire hazard environment power device design code" (GB50058-92) for the design of electrical parts, and in strict accordance with the provisions to report to the fire department for review, acceptance, for the future fire safety work to lay a
。
5.
3 Strengthen the inspection and acceptance of the construction of engineering projects, ensure that the quality of electrical installation projects meets the requirements, and prevent the occurrence of electrical fire hazards
, first of all, we must strictly control the purchase of materials and equipment required for electrical installation projects.

At present, the electrical products on the market, good and bad, to insulated wires as an example, the actual cross-sectional area of common counterfeit and inferior products on the market is less than 10% of the nominal cross-sectional area; Some are marked as 100 meters in length, but in fact they are only more than 80 meters; Some cores have broken strands; Some insulation layers are unevenly thick, and the toughness is poor, easy to disassemble and so on
.

Most of these manufacturers are small township enterprises without production licenses
.

Therefore, in the procurement of materials, we must pay attention to the manufacturer of the product, the production license and the product inspection certificate, etc.
, not greedy
.

In the construction process, the installation and construction should be carried out in strict accordance with the requirements of the design drawings and the relevant electrical installation acceptance specifications
.

In particular, it is necessary to do a good job in small parts according to the requirements of the
norms.

To ensure that each wire (body) contact is closely connected and in good contact, if necessary, the conductor contact surface is coated with electrical grease to ensure the contact area
.

Cable lines in explosive gas atmospheres in zone 1 are strictly prohibited from having intermediate heads, and cable lines in zone 2 and zone 10 and 1 in explosive gas environments should not have intermediate heads
.

The metal housing of electrical equipment in an explosion hazard environment should be reliably grounded and a special grounding wire
should be used.

When using aluminum core wires or cables in explosive hazardous places, the connection and sealing of wires or cables should be crimped, welded or brazed; The cross-section of the ground wire (or neutral line) must be guaranteed
.

The grounding (zero) terminals with the equipment must be well crimped; Grounding and zeroing cannot be mixed; When the wire is connected to the terminal block, a gasket must be added; For multi-stranded wires or soft wires, it is necessary to crimp or solder the wiring nose; There must be no more than two wires connected to each terminal, and so on
.

The inspection and acceptance of the quality of the project is a very critical link
.

The personnel responsible for this work must strictly control the quality, follow up and inspect from the beginning to the end of the installation project, and urge the construction personnel to complete each work
in strict accordance with the specifications.

5.
4 Establish a sound and perfect safe electricity management system, and strictly implement it, and establish a sound electricity management system to prevent electrical fires, from top to bottom, with clear layers and responsibilities to everyone
.

For new or transferred electricity loads, the technical management department shall be responsible for
the connection of new lines and the temporary construction power supply.

The seven management systems of electrical operation safety organization measures should be strictly implemented in the seven management systems of electrical operation safety organization measures, and safety technical measures
should be conscientiously done.

Electrical staff must strengthen safety technology vocational training, strict assessment standards, adhere to the certificate online operation
.

We should adhere to the system of roving inspections, deal with problems in a timely manner, and eliminate hidden situations
.

Equipment operation positions, must be implemented, shutdown and power off system, responsibility to the implementation of people
.

In short, improving the system strictly implements responsibility to people, and rewards and penalties are clear, which is a more reasonable way to prevent electrical fire hazards
.

5.
5 Accelerate the rectification of old enterprises, reduce the hidden dangers of electrical fire to a small At present, most old enterprises have different degrees of aging of electrical lines and components, and some are quite serious
.

According to the current fire situation, the old enterprises must earnestly grasp the rectification of electrical fire hazards
.

First of all, it is necessary to conduct internal self-inspection of the enterprise, implement the funds for rectification according to the problems detected, and require corresponding preventive measures for hidden dangers that cannot be rectified in time, and special personnel are responsible for inspection and management
.

Secondly, it is necessary to ask the fire department to further inspect and conscientiously complete the rectification work
.

5.
6 Combined with the new fire protection requirements, install electrical fire monitoring equipment and systems to build new wood processing enterprises, in strict accordance with the requirements of national standards and specifications in electrical design, through electrical fire monitoring equipment to prevent and protect low-voltage distribution systems, to prevent electrical fire accidents
.

Due to the aging of lines and electrical equipment, electrical accidents occur frequently, and more should be installed by installing electrical fire monitoring equipment and systems to improve the safety of the system and reduce fire accidents
caused by electrical faults.

6 Calculation method of electrical equipment and line selection used by wood processing enterprises Enterprises should constantly carry out technological transformation and adjustment
of production structure in the production process.

In order to meet the needs of production, electrical equipment and wiring also require corresponding adjustments
.

In this case, it is generally up to the company's own engineering and technical personnel to complete its design work
.

Here is a brief introduction
to the calculation methods of electrical equipment and circuit selection commonly used in wood processing enterprises.

6.
1 The selection of electrical equipment, under the premise of determining the explosion and fire hazard level of the equipment installation area, should be in accordance with the "Explosion and Fire Hazard Environment Power Device Design Code" (GB50058-92) in the "Explosion and Fire Hazard Environment Power Device Design Code" (GB50058-92) in the selection table of various electrical equipment explosion-proof structure selection table and various electrical equipment protection structure selection table selection table suitable for the explosion and fire hazard level of its installation area
.

6.
2 Selection of electrical circuits First of all, according to the explosion and fire hazard level of each production area, in accordance with the requirements of the "Design Code for Electrical Installations in Explosion and Fire Hazardous Environments" (GB50058-92),Determine the type of wire, cable, smaller cross-section, direction and laying method of the line, etc
.

Secondly, according to the number of equipment carried by the power supply line, the motor power and the operation mode of the equipment, the calculation current of the line and the calculation load and the load working time
are determined.

The calculation of current and calculation load of the line requires the coefficient method, the utilization factor method, the area power method and the index method, etc.
, and the designer can choose the corresponding method for calculation
according to the needs.

The selection of wire and cable cross-section should be based on the line calculation current less than the carrying capacity of the corresponding working time of the wire under certain laying conditions, and the heat dissipation conditions
of the line laying section should be considered.

After the cross-sectional area of the wire is selected, the voltage loss verification must also be carried out according to the laying of the line, and the allowable voltage loss of the low-voltage line with general power load is 5%.


The allowable voltage loss of low-voltage lines with lighting loads is 3% to 5%.


The end is then calibrated
in accordance with the requirements of the relevant chapters of the Code for the Design of Electrical Installations in Explosion and Fire Hazardous Environments (GB50058-92).

6.
3 The configuration of electrical protection is generally used by wood processing enterprises to distribute transformers, motors and low-voltage power supply lines below 10kV, and the selection method of electrical protection is: (1) transformer protection Transformers below 400kVA generally use high-voltage drop insurance protection
.

The choice of drop insurance should first determine its rated voltage as the operating voltage, and then determine the rated current of the melt according to the larger working current
of the transformer multiplied by a factor.

In the woodworking industry, the larger power motor generally has a starting device, in the determination of the coefficient can not consider the motor self-starting, the system is generally 1.
1 ~ 1.
3
.

400kVA ~ 800kVA transformer, if the enterprise only has a special transformer, the power industry bureau generally requires SF6 high-voltage circuit breaker (with short-circuit protection and over-current protection)
on the high-voltage side of the transformer.

Its choice is generally determined
by the relevant departments of the Electricity Bureau.

If the enterprise has more than two special transformers, it should set up a high-voltage distribution room to complete the functions
of high-voltage distribution, protection of high-voltage distribution lines, transformer protection and reactive power centralized compensation.

(2) Motor protection and starting mode The motors used by woodworking enterprises are generally 380V low-voltage converter motors, and high-voltage motors
are rarely used.

Most of the power of the motor is below 75kW, and only a few of the supporting motors of the equipment reach more than 75kW, such as the thermal mill used in the fiber plate line
.

Under normal circumstances, the production equipment is equipped with a motor when it leaves the factory, and the use only needs to check the type of the motor equipped with the equipment according to the fire and explosion protection level of the installation site
.

Before choosing protection, the starting mode
of the motor should be determined in accordance with the relevant chapters of the "Design Code for Power Installations for Industrial and Civil General Equipment" GBJ55-83.

High-power winding motors mainly use frequency-sensitive varistor starting mode
.

At present, the frequency-sensitive varistor is composed of built-in and external two, because the built-in frequency-sensitive varistor has no contacts, directly installed on the rotor shaft, and the rotor winding is connected
in series.

At start-up, the impedance can be automatically changed with the change of frequency, and the stepless start
of the motor is realized.

Proper selection of parameters can obtain mechanical properties
such as close to constant torque.

It has the advantages of simple wiring, smooth starting, low cost, convenient maintenance, no spark, etc.
, and it is recommended to give
preference.

In 1990, the three thermal mills of our fiber branch replaced the original external frequency sensitive rheoston with a built-in frequency sensitive rheoster, which had a very good effect after several years of operation, and the maintenance workload and maintenance costs were greatly reduced
.

The step-down start of the squirrel cage motor generally adopts two ways, such as autotransformer buck start and star triangle start mode, and when the mechanical starting torque is not high, the star triangle start method
can be selected.

The protection of the motor should be selected
in accordance with the relevant chapters of the "Design Code for Power Devices of Industrial and Civil Equipment" GBJ55-83.

In woodworking enterprises, due to the low power of the motor used, the more commonly used motor protection devices are: fuses + thermal breakers and automatic air switches + thermal relays
.

Fuses and automatic air switches are mainly used as short circuit protection and overcurrent protection of motors, and thermal relays are mainly used as overload protection
of motors.

Improper selection will leave a fire hazard
.

Parameters
should be carefully selected and matched according to the design manual.

3) Low-voltage line protection In order to prevent indirect electric shock, electrical circuit damage and electrical fire in the event of electrical failure, the low-voltage distribution line should be installed with short-circuit protection overload protection and grounding fault protection
according to requirements.

The action of the upper and lower levels of the low-voltage distribution line protection appliances should be selective, and the coordination between all levels should be able to coordinate, but for non-critical loads, there can be no selective cut-off
.

The distribution line should be equipped with short-circuit protection, and the protective electrical appliances should be installed on the power supply side of each circuit, the branch of the line and the line ampacity reduction, within 3 meters from the connection between the protected line and the power line, and not close to the combustibles
.

Appliances used for line short-circuit and overload protection are: fuses, automatic air switches
.

The protection of low-voltage distribution lines should comply with the "Low-voltage Distribution Devices and Stages Design Code" GBJ54-83
.

In addition to determining the rated current value and protecting the set current value, the protection of the low-voltage distribution line should also be carried out to check the interstage coordination of the protection electrical appliance and the coordination calibration of the protection electrical appliance and the distribution line, so as to achieve the reasonable protection of the electrical equipment, the distribution line and the personal indirect electric shock when the low-voltage line is short-circuited or overloaded, and reduce unnecessary power
outages.

The end is then calibrated
in accordance with the requirements of the relevant chapters of the Code for the Design of Electrical Installations in Explosion and Fire Hazardous Environments (GB50058-92).

4) The configuration of low-voltage line electrical fire monitoring equipment and system electrical fire monitoring system is mainly through the residual current type electrical fire detector, fault arc detector and electrical fire limited protector installed in each distribution circuit, the residual current, overcurrent, overvoltage, temperature, fault arc and other signals of the line are collected and monitored, to achieve early warning and alarm of electrical fire, and when necessary, the loop that cuts the signal exceeds the standard.
The short-circuit circuit is short-circuit arc extinguishing protection to achieve the purpose of
prevention and protection.

The following figure shows the electrical fire monitoring configuration scheme of the distribution system of a wood-plus enterprise, which adopts the monitoring system and monitoring settings
of the Acquaris brand.

The low-voltage distribution circuit of this scheme is equipped with the residual current electrical fire detector of the Acquaris ARCM series to monitor the residual current and cable temperature
of each circuit.

The lighting circuit is equipped with a fault arc protector of the AFDD series to monitor the fault arc in the circuit and protect
it.

The distribution circuit of the warehouse is equipped with an ASCP series of electrical fire restrictive protectors for short-circuit arc extinguishing protection
of the line.

After all monitoring equipment is networked through RS485 bus, the data is uploaded to the Acrel-6000/B electrical fire monitoring host to realize remote centralized monitoring of all monitoring
data.

The product selection table of the scheme is shown in the following table: the electrical fire monitoring system of the enterpriseSince its operation, a total of 6 line leakage faults and 3 faulty arc faults have been alarmed and checked, which has avoided greater electrical safety hazards due to faults and played a positive role
in preventing electrical fire accidents.

7 Summarize the fire protection requirements of wood processing enterprises as fire hazard sites
.

The traditional old enterprises have not met the requirements of the new electrical fire protection specifications in the electrical safety design, and in order to improve the safety of the power supply system, it is necessary to transform
the power distribution system.

With the continuous emergence of new electrical fire prevention technology and fire prevention equipment, combined with new specification requirements, electrical fire monitoring equipment and systems can be used to achieve the prevention, alarm and protection of electrical fires and reduce the occurrence
of electrical fire accidents.

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Water Conservancy and Electric Power Press,1994,122 Design Code for Industrial and Civil Power Installations.
China Architecture and Building Press,1990,93 Fire Inspection Manual.
Shanghai Science and Technology Press,1982,124 Li Pingsheng.
Discussion on electrical fire hazards and preventive measures of wood processing enterprises.
Sichuan Forestry Science and Technology.
1999,6(20)5 Enterprise Microgrid Design and Application Handbook.
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