Why Does Explosion-proof Motor Heat Up?

Aug 23, 2024

When an explosion-proof motor is running under load, the power inside the motor is constantly being lost, turning it into heat energy, which will cause the temperature of the explosion-proof motor to rise, exceeding the ambient temperature. The value at which the motor temperature is higher than the ambient temperature is called temperature rise. The greater the power loss, the higher the temperature.
When the explosion-proof motor is running under load, starting from maximizing its function, the larger the load it carries, the better (if mechanical strength is not considered). But the higher the output power, the greater the power loss, and the higher the temperature. We know that the weak temperature resistance inside the motor is insulation materials, such as enameled wires. There is a limit to the temperature resistance of insulation materials. Within this limit, the physical, chemical, mechanical, electrical and other properties of insulation materials are very stable, and their working life is generally about 20 years. Beyond this limit, the lifespan of the insulation material will sharply shorten, and it may even burn out. This temperature limit is called the allowable temperature of the insulation material. The allowable temperature of insulation material is the allowable temperature of the motor; The lifespan of insulation materials is generally the lifespan of motors
When under load, if the rated power of the explosion-proof motor is too high, the motor often operates under light load, and the capacity of the motor itself cannot be fully utilized, becoming a "big horse pulling a small car". At the same time, the low operating efficiency and poor performance of the motor will increase operating costs. On the other hand, if the rated power requirement of the motor is small, it is like a "small horse pulling a big car". If the motor current exceeds the rated current, the internal wear and tear of the motor will increase, and the efficiency will be low. When it is a small matter, it will affect the service life of the motor. Even if the overload is not too much, the service life of the motor will be reduced significantly; Overloading can damage the insulation performance of motor insulation materials and even burn them out. Of course, if the rated power of the motor is small, it may not be able to drag the load at all, which can cause the motor to be in the starting state for a long time and become overheated and damaged. So the rated power of the motor should be strictly selected according to the operating conditions of the electric vehicle.
The impact of changing steel plate base to cast iron base on the temperature rise of explosion-proof motors
The original design of a certain model of 315 series motor was a steel plate base. In order to shorten the manufacturing cycle, improve production efficiency, facilitate management, reduce costs, and improve economic benefits, an explosion-proof motor factory once changed the original steel plate base to a cast iron base while keeping the installation size of the motor unchanged, the electromagnetic design, ventilation components, fans, and hoods of the motor unchanged. The original design of a certain model of 315 steel plate machine base had five lengths (unit: mm): 754, 816, 844, 884, 944, with 6 × 40 flat steel fins and an angle of 5 ° 30 'between the fins. After changing to a cast iron machine base, there are only two lengths: the S machine base is 754, and the M and L machine bases are 844. The height of the heat sink is still 4O, and the width of the heat sink is 8 at the top and 8 at the bottom. The angle between the heat sinks is 5 "37. The machine base is shortened by 0 to 100, and the heat dissipation area is correspondingly reduced. Through several specifications of trial production, it was found that the temperature rise of the explosion-proof motor did not increase, but slightly decreased, as shown in the table below. The main reason for the decrease in temperature rise of explosion-proof motors is that the heat sink of the steel plate base is welded, which is greatly affected by the welding process. Whether the heat sink is truly integrated with the base cylinder is a key factor affecting the thermal conductivity channel, which is one of the important factors determining the heat dissipation effect. The heat sink of the cast iron machine base is integrated with the machine base cylinder, with a wide bottom surface and an increased contact area with the machine base, resulting in good thermal conductivity. Although the total heat dissipation area is relatively reduced, the existing heat dissipation area is fully utilized, allowing the heat of the motor system to be smoothly conducted to the surface of the heat sink and dissipated.
Analysis of the causes of heating faults in explosion-proof motors
Explosion proof motor heating fault refers to the temperature of the explosion-proof motor exceeding the range specified on the nameplate during operation. The cause analysis of the explosion-proof motor heating fault is as follows:
1) The temperature rise exceeds the nameplate specifications under rated load. Regardless of the situation, it is a fault with the motor and must be stopped for inspection, especially when there is a sudden increase in temperature rise.
The external reasons include: low grid voltage or excessive line voltage drop (more than 10%), heavy load (more than 10%), and improper coordination between motors and machinery;
Internal reasons include: single-phase operation, turn to turn short circuit, phase to phase short circuit, stator grounding, fan damage or loose fastening, air duct blockage, bearing damage, rotor stator rubbing, motor and cable joint heating (especially copper aluminum or aluminum aluminum connection), motor corrosion or moisture, etc.
2) Under rated load, the temperature rise did not exceed the temperature rise limit, but due to the ambient temperature exceeding 40 ℃, the motor temperature exceeded the relatively large allowable operating temperature. This phenomenon indicates that the explosion-proof motor itself is normal. The solution is to manually lower the ambient temperature. If this is not possible, the load must be reduced during operation.
When under load, the power of the explosion-proof motor is constantly damaged, and the temperature gradually rises. Therefore, we should troubleshoot according to various specific situations.