Heating and Cooling of Electric Motors

1.When the heating motor of the motor is working, there are mainly iron losses, copper losses, and mechanical losses inside, which are manifested in the form of heating, causing the motor to heat up. When the load and speed of the motor are constant, the internal heat generation is constant per unit time. When an electric motor is working, the heat generated inside it has two functions: on the one hand, it is absorbed by the motor to increase its own temperature, and on the other hand, it dissipates heat to the surrounding environment. The following formula can be used to express this Thermal equilibrium relationship: calorific value=heat absorption+heat dissipation.
When the motor temperature rises, the temperature difference with the surrounding environment will be generated. We refer to the difference between the temperature of the motor itself and the standard ambient temperature (40 C) as the temperature rise, denoted by. When the temperature of the motor rises to a certain value, all the increased heat generated inside the motor is emitted to the surrounding environment, and the temperature of the motor itself no longer increases, indicating that the temperature has reached a stable value. The state when the temperature of the motor reaches a stable value is called the thermal stable state, and the corresponding temperature value is called the steady-state temperature. The corresponding temperature rise is called the steady-state temperature rise.

2. The cooling process of an electric motor refers to the temperature rise change process when the initial temperature rise is greater than the steady-state temperature rise. According to equation (7-1), the temperature rise curve of the motor cooling process can be obtained, as shown in Figure 7.2. Curve 1 corresponds to the situation where the steady-state temperature rise of the motor is zero, meaning that the temperature rise decreases from the moment the motor is disconnected from the power source until it reaches zero. Curve 2 corresponds to the situation where the steady-state temperature rise of the motor decreases to a certain state of temperature rise, that is, the temperature rise decreases from the moment the motor load is reduced until it reaches the corresponding steady-state temperature rise after the load is reduced.
 

Temperature rise curve during motor cooling process

At the beginning of cooling, the initial temperature rise is relatively large, that is, the temperature difference between the motor and the surrounding environment is large, and more heat is dissipated into the surrounding environment, resulting in a faster decrease in the temperature rise of the motor. As the temperature rise decreases, the temperature difference between the motor and the surrounding environment gradually decreases, and the heat emitted to the surrounding environment gradually decreases, slowing down the temperature rise and decrease speed of the motor. This continues until the temperature rise of the motor reaches a steady-state value, and the cooling process ends.

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