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What is the maximum temperature of various parts of the motor?

Date:2023-12-05   Author:XINDA MOTOR
What is the temperature limit of different parts of the motor to ensure the normal operation of the motor? For example, what is the best temperature of the motor casing and what is the temperature limit at the motor bearings? These are all things that need to be understood. Let’s take a look below!
Temperature limits for various parts of the motor
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Generally speaking, if the motor insulation level is Class A and the ambient temperature is 40°C, then the motor shell temperature should be less than 60°C.

1. The temperature rise of the core in contact with the winding (thermometer method) should not exceed the temperature rise limit of the winding insulation in contact (resistance method), that is, Class A is 60℃, Class E is 75℃, Class B is 80℃, F Grade 100℃, Grade H 125℃.

2. The temperature of rolling bearings should not exceed 95°C, and the temperature of sliding bearings should not exceed 80°C. Because the temperature is too high, the oil quality will change and the oil film will be destroyed.

3. In practice, the temperature of the casing is often based on whether it is not hot to the touch.

4. The stray loss on the surface of the squirrel cage rotor is very large and the temperature is high. Generally, it is limited to the extent that it does not endanger the adjacent insulation. It can be estimated by applying irreversible color-changing paint in advance.

Motor temperature and temperature rise

To measure the degree of motor heating, "temperature rise" is used instead of "temperature". When the "temperature rise" suddenly increases or exceeds the maximum operating temperature, it means that the motor has failed. Some basic concepts are discussed below.

Insulation grade of insulation material
Insulation materials are divided into seven grades: Y, A, E, B, F, H, and C according to their heat resistance. Their ultimate operating temperatures are 90, 105, 120, 130, 155, 180°C, and above 180°C respectively. Performance reference temperature (℃) A80 E95 B100 F120 H145

Insulation materials can be divided into the following 7 levels according to thermal stability:
1. Y grade, 90 degrees, cotton
2. Class A, 105 degrees
3. Class E, 120 degrees
4. Grade B, 130 degrees, mica
5. Class F, 155 degrees, epoxy resin
6. H grade, 180 degrees, silicone rubber
7. Grade C, above 180 degrees

The internal insulation material of commonly used Class B motors is often Class F, while the copper wires may use Class H or even higher to improve their quality.

Generally, in order to improve the service life, high-level insulation requirements are often stipulated, and the lower level is assessed. For example, common F-class insulated oil pump motors are assessed as B-class, that is, their temperature rise cannot exceed 120 degrees (leaving 10 degrees as a margin to avoid excessive temperature rise of individual motors caused by process instability).

The so-called ultimate operating temperature of the insulating material refers to the temperature of the hottest spot in the winding insulation when the motor is running within the expected design life. According to experience, the service life of Class A materials at 105°C and Class B materials at 130°C can reach 10 years. However, in actual situations, neither the ambient temperature nor the temperature rise will reach the design value for a long time, so the general service life is 15 to 20 years. Year. If the operating temperature exceeds the ultimate operating temperature of the material for a long time, the aging of the insulation will be accelerated and the service life will be greatly shortened. Therefore, when the motor is running, the temperature is one of the main factors in the life of the motor.

The insulation grade of a motor refers to the heat resistance grade of the insulation material used, which is divided into grades A, E, B, F, and H. The allowable temperature rise refers to the limit of the temperature increase of the motor compared with the ambient temperature. In electrical equipment such as generators, insulation materials are the weakest link. Insulating materials are particularly susceptible to the effects of high temperatures, which can cause accelerated aging and damage. Different insulation materials have different heat resistance properties, and electrical equipment using different insulation materials has different abilities to withstand high temperatures. Therefore, general electrical equipment stipulates the maximum temperature for its operation.