(A) the transformer in household appliances is the root cause of the fire.
The transformer of household appliances generally consists of iron core, primary coil and secondary coil. The primary coil is connected to an AC power supply, and the secondary coil is connected to a load. When the transformer is working, there will inevitably be some energy loss in the process of electromagnetic energy conversion, so the transformer will heat up. Even after the load of the secondary coil is disconnected, because the primary coil is still energized, there is still a certain amount of current on the coil, that is, no-load current. In general, this no-load current can be ignored, even if the transformer is electrified for a long time, it is only a little hot at most. In many household appliances, the primary coil of the power transformer has no switch and is directly connected to the power supply. As long as the transformer is reliable, there is generally no problem in unplugging the power plug. However, if the transformer coil is damaged in the manufacturing process or in the use process, and the specified insulation capacity cannot be reached, turn-to-turn short circuit of the coil may occur after long-term power supply. Once this local short circuit occurs, the current will increase, which will aggravate the transformer heating. After the transformer temperature rises, the coil insulation is further damaged and the current is further increased. Due to the increasing current, the fuse on the line often cannot be blown in time. If this vicious cycle continues, when the temperature rises enough to ignite the insulation, the transformer will start to burn. Therefore, if the transformer is energized for a long time, it may cause a fire.
(2) insufficient power cord capacity and aging insulation.
Most of these happened in old houses. With the increasing number of household appliances, the load of power cord also increases, which makes the original power cord overload. In addition, the ceilings of these old houses are mostly wooden structures, which are particularly dry. In addition, because the power cord has not been replaced for many years, the skin naturally ages, so once the power cord is overloaded and heated, it is easy to cause a fire.
(three) in violation of the rules for the use of electrical appliances
A considerable number of household appliances fires are caused by violation of safety operation regulations. Carelessness, dereliction of duty and non-compliance with operating rules are the biggest causes of fire. Some families do not read the instructions and pay attention to warnings after buying household appliances, and they operate incorrectly; Some families use electric water heaters, electric irons, rice cookers and other heat source appliances, unattended, close to flammable materials; Some families never unplug household appliances such as computers, televisions, stereos, etc., resulting in long-term electrification of electrical components and long-term heat storage causing electrical failures and fires; Some people have a weak awareness of safe use of electricity, just for convenience. They do not follow the electricity management regulations and wiring requirements, illegally pull wires or arbitrarily cut off protection wires, and use copper wires, aluminum wires and iron wires instead of fuses for household or electrical appliances.
(four) poor quality of electrical appliances or lack of awareness of safe use of electricity.
1. Some families ignore the quality of electrical appliances when choosing household appliances and use fake and shoddy electrical products. The electrical distribution control system itself has low protection and poor reliability, which can not effectively protect the safety of electrical equipment. When there is a short circuit or overload, it cannot be automatically protected, and there is a danger of fire at any time.
2. Some families have a weak awareness of safe use of electricity. In real life, they only consider their own convenience, do not follow the electricity management regulations and wiring requirements, illegally connect wires or cut them at will, and replace fuses with copper wires, aluminum wires and iron wires.
3. Failure to use household appliances correctly, such as electric water heaters, electric irons, rice cookers, etc., failure to turn off the power supply in time when leaving, or failure to unplug the power supply when using household appliances such as computers, televisions, stereos, etc., resulting in the appliance itself still being partially energized, resulting in electrical failure and fire caused by long-term heat storage.
Question 2: What is the main cause of fire in electrical equipment? The causes of electrical fires are nothing more than overcurrent, short circuit and reduced conductor insulation. The use environment of electrical appliances includes the short circuit and overcurrent of the load itself. It is common that wires and electrical components are aging. There is also a fire caused by overheating due to the failure of current protection caused by long-term heavy current. As long as you always pay attention to whether the wires of your electrical equipment are aging and whether the protection is out of order, there will generally be no electrical fire. The fire of electric blanket for the elderly in winter is caused by the use environment. Wearing cotton trousers and a quilt, I didn't realize that the electric blanket was overheated until it caught fire.
Question 3: What is the main cause of electrical fire? The main causes of equipment fire are: 1, overheating of electrical lines and equipment, such as short circuit, overload, poor contact, fever and poor heat dissipation. 2, electric spark and arc
Question 4: What is the main cause of fire in household appliances? The weather of refueling is mainly fire caused by electrical appliances.
The most fundamental thing is not to sign the money, the power supply of household appliances, in this case, if there is a fault inside, it will ignite the machine.
Question 5: What is the main cause of the fire in the electrical circuit? The main reasons are short circuit, overload or excessive contact resistance, causing sparks and arcs or overheating of wires and cables, thus causing fires.
1. Short circuit: The wires in the electrical circuit are connected with each other, and the phase wire is connected with the neutral wire (ground wire) for various reasons. The phenomenon that the current in the circuit suddenly increases is called short circuit. According to ohm's law, the current will suddenly increase due to the sudden decrease of resistance during short circuit. So when the line is short-circuited, it will emit a lot of heat in a very short time. This kind of heat can not only burn the insulation layer, but also melt the metal, making the adjacent flammable and combustible substances burn, thus causing a fire.
(B) the form of short circuit
The connection between phase lines is called interphase short circuit; The connection between the phase line and the neutral line (ground wire) is called direct grounding short circuit; The connection between the phase line and the grounding conductor is called indirect grounding short circuit.
(3) The main reasons for short circuit of electric circuit are:
1. When using insulated wires and cables, the insulation is not selected according to the specific environment, so that the insulation is affected by high temperature, humidity or corrosion, and the insulation capacity is lost.
2. The line is in disrepair, and the insulation layer is old, aging or damaged, which makes the core * * *.
3. Overvoltage of power supply leads to insulation breakdown of wires.
4. Installation and maintenance personnel connect the wrong wires, or live work causes artificial short circuit.
5. Bare wires are installed too low, and metal objects accidentally touch wires; There are metal objects or small animals falling on the line, causing jumpers between wires.
6. The overhead line spacing is too small, the span is too large, the wires are slack, and two wires may collide; Overhead power lines are too close to buildings and trees, resulting in contact with buildings or trees.
7. The mechanical strength of the wire is not enough, which causes the wire to break and touch the ground, or break on another wire.
8. Failing to connect privately as required, resulting in short circuit due to poor management and improper maintenance. 9. The insulator of high-voltage overhead line has low withstand voltage, which leads to short circuit to ground.
(4) Measures to prevent short circuit
1. When installing wires according to environmental characteristics, the requirements of humidity, chemical corrosion, high temperature places and rated voltage should be considered.
2. There should be a certain distance between wires, between walls, ceilings and metal components, and between insulators and porcelain bottles that fix wires.
3. Wires 2m from the ground and passing through floors and walls should be protected and insulated to prevent damage. 4. Don't tie the insulated wire with iron wire, but hang it with nails. 5. Measure the insulation resistance regularly. 6. The installation lines shall be installed by qualified electricians. 7. Install the corresponding fuse or automatic switch.
Second, the overload (overload)
(1) Definition: The amount of current allowed to pass continuously in a wire without overheating the wire is called safe current carrying capacity or safe current. If the current flowing through the conductor exceeds the safe current value, it is called conductor overload. Conductor overload is generally based on temperature rise, regardless of voltage drop.
The maximum allowable working temperature of a general conductor is 65 degrees. When overload occurs, the temperature of the conductor exceeds this temperature value, which will accelerate insulation aging and even damage insulation, resulting in short-circuit fire accidents.
(2) The main reasons for overload are:
1. The cross-sectional area of conductor is improperly selected, and the actual load exceeds the safe current carrying capacity of conductor.
2. Too many or too many electrical devices are connected to the line, which exceeds the load capacity of the distribution line.
(3) Measures to prevent overload 1. Reasonable selection of conductor section.
2. Don't pull the wire too much and connect the load.
3. Regularly check the line load and equipment increase or decrease.
4. Install the corresponding safety or automatic switch.
Third, the contact resistance is too large.
(1) Definition: When conductors are connected, the resistance formed on the contact surface is called contact resistance. If the joint is handled well, the contact resistance is small; Poor connection or other reasons will lead to excessive local contact resistance, which will lead to temperature rise, metal discoloration and even melting, and combustible substances in insulating materials will burn.
(2) The main reasons for excessive contact resistance are:
Poor installation quality leads to poor connection between wires and between wires and electrical equipment.
The joint of the conductor is stained with impurities, such as oxide layer, soil, oil pollution, etc.
The connection point is loose due to long-term vibration or cold and hot changes.
4. When copper and aluminum are mixed, due to improper joint treatment, the contact resistance will increase rapidly under the action of electro-corrosion.
(3) Measures to prevent excessive contact resistance:
It is essential to minimize unnecessary joints ... >>
Question 6: What is the main cause of electrical fire? Electrical fires mainly come from three aspects.
1 short circuit. During short circuit, the current quickly rises to 10- 15 times of the rated current, which makes the wire circuit seriously overloaded and heated, leading to fire.
2. overload. Electrical overload, the electrical itself and the circuit are heated and burned due to overload, causing a fire.
3, static electricity, arc. When flammable materials or gases accumulate, the arc generated by static electricity or poor contact will ignite flammable materials or gases, leading to fire.
Question 7: The main causes of electrical equipment fire are overload, short circuit, insulation aging, cooling device failure, poor contact, grounding discharge, low voltage and so on.
Question 8: Causes of electrical fires Electrical fires mainly include the following four aspects: 1. Leakage fire The so-called leakage fire refers to the decrease of insulation capacity of wires or supporting materials in a certain part of the line due to some reasons (natural reasons or man-made reasons, such as wind and rain, humidity, high temperature, bump, scratch, friction, corrosion, etc.). ), resulting in line-to-line (through damaged insulation, support, etc. ) and between the wire and the earth. When leakage occurs, the leakage current flows into the earth, and local high temperature will be generated when it meets the parts with large resistance, which will cause the nearby combustible materials to catch fire, thus causing a fire. In addition, the leakage spark generated by the leakage point will also cause fire. Second, short-circuit fire After the insulator of the bare wire or insulated wire in the electrical circuit is damaged, the live wire and the adjacent wire, or the live wire and the ground wire (including the grounding subordinate to the earth) contact at a certain point, causing a sudden and substantial increase in current, which is called short circuit, commonly known as touching the wire, mixing the wires or connecting the electricity. Because the resistance suddenly decreases and the current suddenly increases during short circuit, its instantaneous calorific value is also very large, which greatly exceeds the calorific value when the line works normally. Strong sparks and arcs are easily generated at the short circuit point, which can not only make the insulation layer burn rapidly, but also melt the metal, causing the burning of flammable and combustible substances nearby and causing fires. Third, overload fire The so-called overload means that when the current in the conductor exceeds the safe current carrying capacity, the temperature of the conductor continues to rise. This phenomenon is called conductor overload. When the conductor is overloaded, the aging and deterioration of the conductor insulation layer are accelerated. When seriously overloaded, the temperature of the conductor will continue to rise, even leading to insulation burning of the conductor, and can ignite combustible materials near the conductor, thus causing a fire. Fourth, the contact resistance is too large. As we all know, wires are connected with wires, and there are connectors where wires are connected with switches, fuses, instruments and electrical equipment. The resistance formed on the contact surface of the joint is called contact resistance. It is normal that current will generate heat when it passes through the connector. If the joint is handled well and the contact resistance is not large, then the heat at the joint is very small and the normal temperature can be maintained. If there are impurities in the joint, the connection is unreliable or other reasons make the joint contact poor, resulting in excessive local resistance at the contact part. When the current passes through the connector, a lot of heat will be generated here, resulting in high temperature. This phenomenon is that the contact resistance is too large. In a high current circuit, if the contact resistance is too high somewhere, a lot of heat will be generated in the part with too high contact resistance, which will make the metal discolor or even melt, causing the insulation layer of the conductor to burn, leading to the burning of nearby combustible materials or the burning of dust and fibers accumulated on the conductor, thus causing a fire.
prevent
In our daily life, we mainly do the following things: 1, patrol the power lines in order to find problems in time. 2. When designing and installing electrical circuits, the insulation strength of wires and cables should not be lower than the rated voltage of the network, and insulators should be selected according to the different voltages of the power supply. 3. During line installation, it is necessary to prevent scratches, abrasions and contact with the insulation of wires, and pay attention to the quality of wire connection joints and insulation packages. 4. In places with special humidity, high temperature or corrosive substances, it is forbidden to expose insulated wires, and bushing connection should be adopted. In dusty places, lines and insulators should be cleaned frequently to avoid oil pollution. 5. It is forbidden to connect wires randomly. When installing lines, the wires with corresponding sections should be selected reasonably according to the load of electrical equipment. Moreover, the spacing between wires, between wires and building components, and between insulators for fixing wires should meet the requirements of regulations. 6, regularly check the line fuse, choose the appropriate fuse, shall not be arbitrarily rough fuse, more are not allowed to use aluminum wire and copper wire instead of fuse. 7. Check whether all connection points on the line are firm and reliable, and it is required that inflammable and explosive articles shall not be stored nearby.
Precursors and measures
Before an electrical fire, we should pay special attention to a precursor, that is, the wires will first burn the insulation sheath due to overheating, giving off an unpleasant smell of burnt rubber and burnt plastic. Therefore, when you smell this smell, you should first think that it may be caused by electrical reasons. If no other reason can be found, turn off the power immediately until the reason is found out and properly handled. In case of fire, whether it is caused by electricity or not, we must first find a way to cut off the power supply quickly. & gt