Fire causes and preventive measures of the hottest

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Fire causes and preventive measures of motor

motor is an electrical equipment that converts electrical energy into mechanical energy. In the process of use, the motor also has fire risk. Therefore, it is an important content of fire prevention work to study the causes of motor fire and its preventive measures

1 causes of motor fire

the causes of motor fire are mainly caused by improper selection, use, or poor maintenance. Some motors are of poor quality and have hidden dangers inside, so they are prone to failure during operation and cause fire

1.1 if the overload load of the motor exceeds the rated power of the motor and the power supply voltage is too low, the motor will be overloaded. Overload will inevitably cause the motor winding to overheat, even burn the motor, or ignite the surrounding combustibles, causing a fire

1.2 insulation damage if the insulation of motor winding wire is damaged, it will cause inter turn or inter phase short circuit; If the insulation between the winding resistance and the housing is damaged, it will also cause a short circuit to the ground. Short circuit generates a lot of heat, and the wire is in danger of fusing or eventually burning, causing a fire

1.3 poor contact, if each contact or outgoing line contact of the connecting coil is not firmly connected; Poor contact of wire ends; The joint between the rotor winding and the commutator of the DC motor is desoldered, or the brush is poorly ground after replacement, and the contact with the slip ring is not good. 6. The displacement measurement resolution (magnetostrictive displacement sensor): 0.01mm, etc., will form a large contact resistance, which will send sparks or arcs, or damage the insulation of the wires around the contact, or cause the motor to run in single-phase, burn the motor, etc., which are all factors leading to the fire

1.4 improper selection of motor if the working environment, power, starting, speed regulation, mechanical characteristics, installation and other requirements are not taken into account, the motor will be prone to failure during operation and cause fire

1.5 after single-phase operation of the motor with load, if it is not found in time, take corresponding measures, it is bound to burn the motor winding, or even catch fire

1.6 mechanical friction the most prominent friction in the operation of the motor is the bearing friction, which will cause local overheating to dilute the lubricating grease and overflow the bearing chamber, and the temperature rise will be higher. When it rises to a certain value, it will ignite the surrounding combustibles. Sometimes the bearing ring is crushed and the rotating shaft is stuck, burning the motor and causing a fire. In addition, if the bearing is seriously worn, it will produce non concentricity and uneven air gap, so that the temperature rise of the friction parts of the rotor and stator can reach more than 1000 ℃, which will damage the insulation of the stator and rotor and short circuit, and even produce sparks in case of serious friction

1.7 excessive iron loss eddy current loss in iron loss is manifested in core heating. If the quality and specification of iron core silicon steel sheets do not meet the requirements, or the insulation strength between sheets is too low, eddy current loss will be too large and a lot of heat will be generated. If the motor drives the load, overload will inevitably occur

1.8 poor grounding device when the motor winding is short circuited to the housing, if there is no reliable protective grounding, the housing will be charged. If there are other messy flammable substances piled around the housing, the current will flow from the housing through these substances into the earth, and over time, it will gradually heat up, which may cause a fire

1.9 poor maintenance ① poor maintenance makes dust, fibers and other sundries block the ventilation slot of the motor, hindering heat dissipation, resulting in temperature rise and fire; ② The accumulated dirt makes the bearing heat and expand, and even the bearing is stuck. 2 If the experimental force and displacement do not change and rotate during the experiment, the result is like increasing the load, which greatly increases the coil current and causes the coil to heat up and catch fire

2 fire prevention measures for motors

motor fire accidents can be completely avoided as long as the structure and type of the motor are properly selected, the installation is reasonable, various feasible protective devices are installed, the operation is forced, the operation state is closely monitored, problems are found and solved in time, and the maintenance of the motor is strengthened

2.1 correct selection of motor is the primary problem related to the safe and economical use of motor

2.1.1 select the appropriate protection form according to the working environment. For example, closed motor should be selected in humid environment; Explosion proof motor shall be selected for explosive gas environment. Environmental factors should also consider dust prevention, corrosion prevention, temperature and other conditions

2.1.2 the power of the motor must adapt to the size of the production machinery load and its continuous and intermittent law. The power of the motor should be slightly greater than that of the production machinery. When selecting, the power of the required motor can be calculated in advance according to the actual situation. When selecting the motor power, the ambient temperature should also be considered, and the matching conductor should also be correctly selected

2.1.3 when selecting the motor, in addition to the requirements of environment and power, it is also necessary to consider the speed, starting, speed regulation, mechanical characteristics, installation requirements and other requirements

2.2 the starting method should be appropriate

2.2.1 when the power supply or transformer capacity permits, full voltage starting should be preferred for squirrel cage motors; When its power is greater than 20% of the transformer capacity or its power exceeds 14kw, step-down starting shall be adopted

2.2.2 when the wound rotor motor is started, connect the rheostat in the loop of its rotor winding. For the starting of starting rheostat, for motors with reduced power, general three-phase rheostat or oil immersed starting rheostat can be used; Larger power motors use water resistors

2.3 the installation of the motor shall meet the fire protection requirements

2.3.1 the motor shall be installed on a solid base, and the electric foundation shall be non combustible

2.3.2 a passage with a clear distance of no more than 1m shall be reserved between the foundation periphery of the motor base and the building or other equipment; When there is a passage between the motor and the wall, or the motor installed in rows, the clear distance on the other side can not be less than 0.3m. The distance between the motor and the exposed live parts of low-voltage distribution equipment shall not be less than 1m

2.3.3 combustibles are not allowed to be stacked near the motor, and there shall be no oil stains and oil cotton yarn on the ground; Sundries are not allowed to be stacked near the motor starting equipment; The passage from the motor and the linked machinery to the switch shall be protected and unblocked frequently

2.3.4 a section of power line close to the motor must be protected with metal hose or plastic sleeve. The connection between the hose and the power line pipe must be firmly rolled and fixed with a collet; The connection between the other end and the motor incoming box should also be a fixed fulcrum

2.3.5 the motor and power line pipe shall be effectively grounded. The grounding wire shall be fixed on the bolt of the motor. When the cross section of the grounding wire is used as the main line, it is generally 30% of the incoming line of the motor; However, the maximum section of aluminum core shall not exceed 35mm, and that of copper core shall not exceed 25mm. If rubber insulated conductor is used as branch line, the minimum cross-section of aluminum core is 4mm and that of copper core is 2.5mm. The grounding resistance shall not be greater than 4 Ω; However, if the capacity of the transformer or generator supplying these motors is less than 100kVA, it is allowed to be less than 10 Ω. It is strictly forbidden to insert iron rods into the ground as protective grounding

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