Relationship Between Motor Temperature Rise and Ambient Temperature

Temperature rise is a very important performance index of motor. It refers to the value that motor winding temperature is higher than the ambient temperature under rated operation state.

Insulation materials are divided into 7 grades according to heat resistance: Y, A, E, B, F, H and C, and their limit operating temperatures are 90 ℃, 105 ℃, 120 ℃, 130 ℃, 155 ℃, 180 ℃ and above 180 ℃ respectively. During the motor operation , the ambient temperature is one of the main factors affecting motor’s service life .

Temperature rise is the temperature difference between motor and environment, which is caused by motor heating. The motor iron core in operation will produce iron loss in the alternating magnetic field, copper loss and other stray losses after the winding is energized. These will raise the motor temperature.

On the other hand, motor will also dissipate heat. When the heating and heat dissipation are equal, the equilibrium state is reached, and the temperature will not rise but stabilize at a level. When heat generation increases or heat dissipation decreases, the balance will be destroyed, so the temperature will continue to rise, and the temperature difference will be expanded, the heat dissipation should be increased to reach a new balance at another higher temperature. However,  the temperature rise, has increased than before, so it is an important index in the design and operation of the motor, marking the heating degree of the motor.

For the motor normal operation, it is actually affected by factors such as ambient temperature.

(1) When the temperature drops, motor temperature rise will decrease slightly. This is because the winding resistance decreases and the copper consumption decreases. When the temperature drops by 1 ℃, the resistance drops by about 0.4%.

(2) For self cooling motor, the temperature rise increases by 1.5 ~ 3 ℃ for every 10 ℃ increase in ambient temperature. This is because the winding copper loss increases with the increase of temperature. Therefore, the temperature change has a great impact on large motors and enclosed motors.

(3) For every 10% increase in air humidity, due to the improvement of heat conduction, the temperature rise can be reduced by 0.07 ~ 0.38 ℃, with an average of about 0.2 ℃.

(4) The altitude is 1000m, and the temperature rise increases by 1% of the temperature rise limit value per 100m.

(1) The iron core temperature rise in contact with the winding shall not exceed the  limit of the winding insulation in contact (resistance method), i.e. 60 ℃ for class A, 75 ℃ for class E, 80 ℃ for class B, 105 ℃ for class F and 125 ℃ for class H.

(2) The rolling bearing temperature shall not exceed 95 ℃, and that of sliding bearing shall not exceed 80 ℃. Too high temperature will change the oil quality and destroy the oil film.

(3) In practice, the casing temperature is often not hot.

(4) The surface stray loss of squirrel cage rotor is large and the temperature is high, which is generally limited to not endangering the adjacent insulation. It can be estimated by painting irreversible discoloration paint in advance.