First, insulation level
The insulating material is divided into Y, A, E, B, F, H, C7 level according to heat resistance, with a limit operating temperature of 90, 105, 120, 130, 155, 180 ° C, and 180 ° C.
The ultimate operating temperature of the so-called insulating material means the temperature of the most hot in the operating time of the motor in the operating life of the motor.
According to experience, the A-grade material is 105 ° C, the B-grade material is over 10 years, but the ambient temperature and temperature rise will not be designed for a long time in actual conditions.
Therefore, the general life is 15 to 20 years. If the operating temperature exceeds the ultimate operating temperature of the material, the insulated aging intensifies and the life is greatly shortened. Therefore, the motor is in operation, and the temperature is one of the main factors of life.
Temperature rises is the temperature difference between the motor and the environment, caused by the heating of the motor. The motor core in the run will produce iron damage in the alternating magnetic field. After the windings are powered on, there will be copper loss, and other strand-tuned losses.
These will increase the temperature of the motor. On the other hand, the motor will also heat it.
When the heat generation is equal to the heat dissipation, the balance is reached, and the temperature is no longer rising and stabilized on one level. When the heat is increased or the heat dissipation is reduced, the balance will continue to rise, increase the temperature difference, increase heat dissipation, reach a new balance at another higher temperature.
But at this time, the temperature difference is increased before, so the temperature rise is an important indicator of motor design and operation, marking the degree of heat generation of the motor, in operation, such as motor temperature rise, It will illustrate that the motor has faults, or the air stop block or load is too heavy.
Second, the relationship between temperature rise and temperature
For normal operating motors, theoretically independent of the temperature rise and ambient temperature under the rated load, but is actually affected by factors such as ambient temperature.
1. When the temperature drops, the temperature of the normal motor will be slightly reduced. This is because the winding resistor R drops, and the copper is reduced. The temperature is 1 ° C, R is 0.4%.
2. For the self-cooling motor, the ambient temperature increases by 10 ° C, the temperature rise is increased by 1.5 to 3 ° C. This is because the winding copper is increased as the temperature rises. Therefore, temperature changes have a large effect on large motors and closure motors.
3, air humidity is 10% higher, due to improvement of thermal conductivity, temperature rise can fall 0.07 ~ 0.38 ° C, with an average of 0.19 ° C.
4, altitude is based on 1 000 m, 1% of temperature rise limit value per liter of 100 m, temperature rise increases.
It is usually said that the limit of the A-level operating temperature is 105 ° C, and the highest allowable operating temperature of the A level is 90 ° C.
What is the difference between the limit operating temperature and the highest allowed working temperature? In fact, this is related to the measurement method, different measurement methods, which reflects different values, and the meaning is different.
Temperature limits of each part of the motor:
1. Core temperature rise (thermometer method) contact with the winding should not exceed the temperature rise limit (resistance method) of the winding insulation, i.e. is 60 ° C, and the E is 75 ° C, the B is 80 ° C, F The stage was 100 ° C, and the H was 125 ° C.
2, the rolling bearing temperature should not exceed 95 ° C, the temperature of the sliding bearing should not exceed 80 ° C. The oil is changed and destroying the oil membrane due to too high temperature.
3, the case temperature practice is often made by non-hot. Electrician: www.dgjs123.com
4, the stray loss of the murine cage rotor is very large, the temperature is high, generally not endangered by the neighboring insulation. It is estimated that non-discrete variability can be pre-brush.
Third, the exclusion of the motor fever failure
When the motor temperature exceeds the highest operating temperature or temperature rise exceeds the specified or temperature rise, it does not exceed the specified, but when the temperature rise is suddenly increased at low load, the motor has failed.
1. The temperature rise under the rated load does not exceed the temperature rise, only because the ambient temperature exceeds 40 ° C, but the motor temperature exceeds the maximum allowable operating temperature.
This phenomenon means that the motor itself is normal. The solution is to use artificial methods to decline the ambient temperature. If it is not available, the load must be reduced.
2. The temperature rise beyond the nameplate under the rated load.
Regardless of the situation, it is a motor failure. It must be downtown, especially to the temperature rise and sudden attention.
Its external reasons are: the grid voltage is too low or the line pressure drop is too large (more than 10%), the load is too heavy (more than 10%), the motor and machinery are not proper; the internal reasons are: single-phase operation, inter-turn, short circuit, inter-turn , Stator grounding, fan damage or uninteral, air-stop blocking, bearing damage, fixed rotor, motor and cable adoptia (especially copper aluminum or aluminum aluminum), motor is corroded or tidy. In addition, from theoretically, the motor can be reversed, but some motor fans have directionality. If it is, the temperature rise will exceed a lot.
In summary, it is necessary to troubleshoot a variety of specific situations. Read more
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