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About motor temperature and temperature rise

Add Date: 2019/6/4    Views: 616

“Warm rise” is an important parameter to measure and evaluate the degree of heat generation of the motor. It is measured under thermal equilibrium when the rated load of the motor is used. The terminal customer perceives the motor as good or bad. The usual practice is to touch the motor and see how the temperature of the casing is. Although it is not accurate, it also generally controls the temperature rise of the motor.
When the motor fails, the most notable initial feature is the “feel” temperature rise abnormality: “temperature rise” suddenly increases or exceeds the normal operating temperature. At this time, if measures can be taken in time, at least large property losses can be avoided, and even a disaster can be avoided.

Motor temperature rise
Temperature rise is the difference between the operating temperature of the motor and the ambient temperature, which is caused by the heat generated when the motor is running. In the running motor core, the iron loss occurs in the alternating magnetic field, and the copper loss occurs when the winding is energized, and other stray losses, etc., which will increase the temperature of the motor.
The motor will also dissipate heat while it is hot. When the heat and heat are equal, the equilibrium state is reached. The temperature does not rise and stabilizes at a level, which is what we often call thermal stability.
When the heat is increased or the heat dissipation is reduced, the balance will be broken, the temperature will continue to rise, and the temperature difference will be widened. We must increase the heat dissipation measures to make the motor reach a new balance at another higher temperature. However, the temperature difference at this time, that is, the temperature rise has increased more than before, so that temperature rise is an important indicator in the design and operation of the motor, which indicates the degree of heat generation of the motor. In operation, if the temperature rise of the motor suddenly increases, Indicates that the motor is faulty, or the air duct is blocked or the load is too heavy.
Relationship between temperature rise and temperature

For a normally operating motor, the temperature rise should theoretically be independent of the ambient temperature, but it is actually related to environmental temperature, altitude and other factors.
● When the temperature drops, the copper loss will decrease due to the decrease in winding resistance, so the temperature rise of the normal motor will be slightly reduced.
● For self-cooling motors, the temperature rise will increase by 1.5~3°C for every 10°C increase in ambient temperature. This is because the copper loss of the winding increases as the temperature rises. Therefore, temperature changes have a great impact on large motors and closed motors, and should be clear to both motor designers and users.
● The air humidity is 10% higher, the heat conduction condition will be improved, and the temperature rise can be reduced by 0.07~0.4°C. Another problem arises from the increase in air humidity, which is the moisture-proof problem in the non-operating state of the motor. For the warm environment, we must take measures to avoid the motor windings from being damp, designed and maintained according to the wet tropical environment.
● When the motor is running in a high altitude environment, the altitude is 1000m. At 100m per liter, the temperature rise increases by 1% of its limit value. This problem is a problem that designers must consider. The temperature rise of our type test does not fully represent the actual operating state. That is to say, for the plateau environment motor, the index margin should be moderately increased by the accumulation of actual data.
Temperature rise and temperature
For motor manufacturers, pay more attention to the temperature rise of the motor, but for the motor end user, it is more intuitive to pay attention to the motor temperature; a good motor product should take into account both temperature rise and temperature to ensure that the motor's performance index and life are consistent. Claim.
The difference between the temperature at a point and the reference (or reference) temperature is called the temperature rise. It can also be called the difference between a certain temperature and the reference temperature. The difference between the temperature of a part of the motor and the surrounding medium is called the temperature rise of the part of the motor; the temperature rise is a relative value.
Heat resistance rating
Within the permissible range and the grades assigned to it, ie the heat resistance rating of the motor. If this limit is exceeded, the life of the insulating material is drastically shortened and even burned. This temperature limit is called the allowable temperature of the insulating material.
Motor temperature rise limit
When the motor is in thermal stability for a long period of time under rated load, the maximum allowable temperature rise of each component of the motor is called the temperature rise limit. The allowable temperature of the insulating material is the allowable temperature of the motor; the life of the insulating material is generally the life of the motor. However, from an objective point of view, the actual temperature of the motor has a direct relationship with bearings, grease, etc. Therefore, these factors should be considered comprehensively.
When the motor load is running, it is better to use the load as much as possible (if mechanical strength is not considered). However, the greater the output power, the greater the power loss and the higher the motor temperature. We know that the weakest temperature resistance in a motor is an insulating material, such as an enameled wire. There is a limit to the temperature resistance of insulating materials. Within this limit, the physical, chemical, mechanical, electrical and other aspects of insulating materials are very stable, and their working life is generally about 20 years.
Insulation class
The insulation rating represents the maximum allowable operating temperature rating of the insulation structure at which the motor can maintain its performance for a predetermined period of use.

The ultimate operating temperature of the insulating material refers to the temperature at which the motor is the hottest in the winding insulation during the expected life of the motor. According to experience, under normal conditions, the ambient temperature and temperature rise will not reach the design value for a long time, so the general life span is 15 to 20 years. If the operating temperature approaches or exceeds the ultimate operating temperature of the material for a long period of time, the aging of the insulation will increase and the life will be greatly shortened.
Therefore, the operating temperature is the main and key factor of the life of the motor. In other words, attention should be paid to the actual operating conditions of the motor while paying attention to the temperature rise index of the motor. According to the severity of the working conditions, sufficient design margin is reserved.
Insulation system
The comprehensive application entity of the electromagnetic wire, insulating material and insulation structure of the motor is closely related to the manufacturing process equipment and technical guidance documents, and is the most confidential technology of the factory. In the motor safety evaluation, the insulation system is considered as a key comprehensive evaluation object.

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