In daily work, customers often come into contact with various problems such as the temperature rise and temperature of electric motors.
In fact, the "temperature rise", not the "temperature", is used to measure the heating degree of electric motors. In order to explain this knowledge point, we below by taking examples to learn the motor temperature rise, temperature problems.
For example, if the temperature rise limit of A grade A insulated motor is 50℃, then:
1. When the air temperature is 15℃ and the winding temperature is 80℃, can the motor continue to operate?
Some people will answer: of course. The reason is: although the temperature rises more than 50℃ up to 65℃, the winding temperature did not exceed group A insulation maximum allowable working temperature of 90℃. And some people said no, because the temperature rise exceeded.
2. When the temperature is 45℃ (such as open air or high temperature workshop in summer) and the winding temperature of the motor is 95℃. Can the motor continue to run?
There are also two opinions: one says no, and the other says yes. The latter reason is that the nameplate does not say that the temperature rise limit is 50℃? It does not exceed this value.
In fact, similar to the above problems are due to the temperature rise, temperature, insulation of heat resistance and heat balance caused by no clear concept.
In order to solve the above questions, first of all, we should know the heat resistance grade of the insulating material. Insulation material is divided into 7 grades according to the heat resistance of Y, A, E, B, F, H, C, and its ultimate working temperature is 90, 105, 120, 130, 155, 180, and 180℃ above.
The limit working temperature of the so-called insulation material refers to the hottest temperature in the winding insulation during the operation of the motor in the design life expectancy. According to experience, the life of grade A material at 105 ° C and Grade B material at 130 ° C can reach 10 years, but the environmental temperature and temperature rise will not reach the design value for a long time under the actual situation, so the general life is 15 ~ 20 years.
If the operating temperature exceeds the material limit for a long time, the aging of insulation will be intensified and the service life will be shortened seriously. Therefore, the temperature is one of the main factors of the life of an electric motor in operation.
About the temperature rise
The temperature rise is the temperature difference between the motor and the environment, which is caused by the motor heating. In the operation of the motor core in an alternating magnetic field will produce iron loss. Copper loss occurs when the winding is energized. There are other stray losses and so on. All of this will raise the temperature of the motor. On the other hand, the motor will also dissipate heat. When the heat is equal to the heat dissipation, it will reach an equilibrium state, and the temperature will no longer rise, but stabilize at the same level. When heat increase or reduce heat dissipation will destroy the balance, so that the temperature continues to rise, expand the temperature difference, increase heat dissipation.
A new equilibrium is reached at a higher temperature. But the temperature difference, or temperature rise, has increased. Therefore, the temperature rise is an important index in the design and operation of the motor, marking the heating degree of the motor. During operation, if the temperature rise of the motor increases suddenly, it means that the motor has faults, the air duct is blocked or the load is too heavy.
