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What is the effect of high ambient temperature on explosion-proof motors?

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Explosion-proof motors generally require an ambient temperature of -20 to 40 °C, a temperature group of T4, and a maximum surface temperature of not more than 135 °C. Will it affect the motor if the ambient temperature exceeds 40°C? The high temperature of explosion-proof motors mainly affects the insulation of motor materials. If the temperature of the insulating material of the motor is too high, it will cause a short circuit and burn the explosion-proof motor. So let’s talk about the insulation materials of explosion-proof motors first.

The insulation class of the motor refers to the heat resistance class of the insulating material used. According to the ability of insulating materials to withstand high temperature, 7 maximum allowable temperatures are specified, which are divided into Y, A, E, B, F, H, C, with a total of 7 grades, and the maximum working temperature is 90°C, 105°C, 120°C , 130°C, 155°C, 180°C and above 180°C.

The iron core in the motor operation will produce iron loss in the alternating magnetic field, copper loss will be produced after the winding is energized, and other stray losses. These increase the temperature of the motor. In this way, there is a temperature difference between the motor and the ambient temperature. When the ambient temperature decreases, the temperature difference increases, the heat dissipation speed increases accordingly, and the motor temperature rise decreases accordingly. Similarly, when the ambient temperature increases, the temperature difference becomes smaller, the heat dissipation speed becomes slower, and the temperature rise of the motor will increase accordingly.

When the heat generated is equal to the heat dissipated, an equilibrium state is reached, and the temperature no longer rises but stabilizes at a level. When the heat generation increases or the heat dissipation decreases, this balance is disrupted, so that the temperature continues to rise and the temperature difference expands. At this time, the heat dissipation should be increased to reach a new equilibrium at another higher temperature. However, the temperature difference at this time, that is, the temperature rise, has increased compared with the previous one. Therefore, the temperature rise is a key indicator in the design and operation of the motor, which indicates the degree of heat generation of the explosion.

In addition, the altitude of the area where the explosion-proof motor is located will also affect the temperature rise of the explosion-proof motor. Due to the thin air in the plateau, the cooling air volume will be reduced. In addition, the thin air makes the magnetic permeability between the rotor and stator worse, which affects the power of the motor. Therefore, the high altitude climate must be explained to the manufacturer. Generally, 1 km is used as the standard, and the temperature rise limit is increased by 1% for every 100 meters. At this time, a special plateau explosion-proof motor is required.

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