About motor temperature and temperature rise
"Temperature rise" is an important parameter to measure and evaluate the degree of motor heating . It is measured under the thermal equilibrium state of the motor at rated load . The usual way for end customers to perceive the quality of a motor is to touch the motor and see the temperature of the casing . Although it is not accurate, it can give a general sense of the temperature rise of the motor .
When a motor fails, the most obvious initial characteristic is an abnormal temperature rise in the "hand feel" : the "temperature rise" suddenly increases or exceeds the normal operating temperature . If you can take timely measures at this time, you can at least avoid major property losses, or even avoid a disaster.
Temperature rise is the difference between the motor's operating temperature and the ambient temperature , which is caused by the heat generated when the motor is running. When the core of a running motor is in an alternating magnetic field, it will produce iron losses, and when the winding is energized, it will produce copper losses, as well as other stray losses, etc., which will increase the temperature of the motor.
The motor will also dissipate heat while generating heat. When the heat generation and heat dissipation are equal, it will reach a balanced state , and the temperature will no longer rise but will stabilize at a level, which is what we often call thermal stability .
When heat generation increases or heat dissipation decreases , the balance will be broken , causing the temperature to continue to rise and the temperature difference to expand. We must take additional heat dissipation measures to make the motor reach a new balance again at another higher temperature . However, the temperature difference at this time, that is, the temperature rise, has increased than before (public account: Pump Butler), so the temperature rise is an important indicator in the design and operation of the motor, marking the degree of heat generation of the motor . During operation, such as If the temperature rise of the motor suddenly increases, it indicates that the motor is faulty, or the air duct is blocked or the load is too heavy.
For a normally operating motor, theoretically the temperature rise should have nothing to do with the ambient temperature under rated load, but in fact it is still related to factors such as ambient temperature and altitude.
● 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 decrease slightly.
● For self-cooling motors, for every 10°C increase in ambient temperature, the temperature rise will increase by 1.5~3°C. This is because winding copper losses increase as the temperature rises. Therefore, temperature changes have a greater impact on large motors and enclosed motors. Both motor designers and users should be aware of this problem.
● For every 10% increase in air humidity, the temperature rise can drop by 0.07~0.4℃ due to improved thermal conductivity conditions. As air humidity increases, another problem arises, which is the problem of moisture protection when the motor is not running. For warm and hot environments, we must take measures to prevent the motor windings from getting damp, and design and maintain them according to the environmental conditions in humid tropical zones.
● When the motor is running in a high-altitude environment, the altitude is 1000m as the standard. For every 100m of liter, the temperature rise increases by 1% of its limit value. This issue is something that designers must consider. The temperature rise value of our type test does not fully represent the actual operating status. That is to say, for motors in plateau environments, the index margin should be appropriately increased through the accumulation of actual data.
For motor manufacturers, they pay more attention to the temperature rise of the motor , but for end customers who use the motor, they pay more intuitive attention to the motor temperature . A good motor product should take into account both temperature rise and temperature to ensure that the performance indicators and life span of the motor meet the requirements. Require.
The difference between the temperature at a certain point and the reference (or base) temperature is called temperature rise. It can also be called the difference between the temperature at a certain point and the reference temperature. The difference in temperature between a certain part of the motor and the surrounding medium is called the temperature rise of that part of the motor; the temperature rise is a relative value.
Within the allowable range and the grade it is divided into, it is the heat resistance grade of the motor. If this limit is exceeded , the life of the insulation material will be drastically shortened, and it may even burn out. This temperature limit is called the allowable temperature of the insulating material .
When the motor reaches a thermally stable state after long-term operation under rated load , the maximum allowable limit of 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 perspective, the actual temperature of the motor has a direct relationship with the bearings, grease, etc., so these related factors should be comprehensively considered .
When the motor is running under load, in order to maximize its function, the larger the load, that is, the output power, the better (if the mechanical strength is not considered). However, the greater the output power, the greater the power loss , and the higher the motor temperature will be. We know that the weakest thing in the motor that can withstand temperature is the insulating material, such as 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 the insulating materials are very stable, and their working life is generally about 20 years.
The insulation level indicates the maximum allowable operating temperature level of the insulation structure at which the motor can maintain its performance during the intended service period.
The ultimate operating temperature of the insulation 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, in actual situations, neither the ambient temperature nor the temperature rise will reach the design value for a long time, so the general life span is 15 to 20 years. If the operating temperature is close to or 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 operating temperature is the main and key factor in the life of the motor. That is to say, while paying attention to the motor temperature rise indicator, the actual operating conditions of the motor should be fully considered, and sufficient design margin should be reserved according to the severity of the working conditions .
The comprehensive application entity of motor electromagnetic wires, insulation materials, and insulation structures is closely related to 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 regarded as a key comprehensive evaluation object.
Insulation performance is a very critical performance indicator of the motor , which comprehensively reflects the safe operating performance and design and manufacturing level of the motor.
In the motor design process, the first consideration is what kind of insulation system to use , whether the insulation system matches the factory's process equipment level, and whether it is leading or lagging behind in the industry. It is particularly important to emphasize that it is most important to act according to one's ability. Otherwise, if the level of process equipment is not up to standard and we blindly pursue leadership, no matter how advanced the insulation system is, we will not be able to produce a motor with reliable insulation performance.
We must take into account these issues
● Conformity of electromagnetic wire selection. The selection of motor electromagnetic wire should match the motor insulation level ; for variable frequency speed regulation motors, the impact of corona on the motor should also be considered. Practical experience has proven that thick paint film motor wires can moderately tolerate the effects of motor temperature and temperature rise, but the heat resistance level of the electromagnetic wire is more important. This is a common problem that many designers tend to misunderstand.
● The selection of composite materials must be strictly controlled. During an inspection at a motor factory, it was found that due to material shortages, production workers would substitute materials that were lower than the requirements of the drawings. This substitution led to great quality risks in the motors .
● Influence on the bearing system. The motor temperature rise is a relative value, but the motor temperature is an absolute value . When the motor temperature is higher, the temperature directly transmitted to the bearing through the shaft will be higher. If it is a general-purpose bearing, the bearing will easily fail. In addition, The loss and failure of grease can easily cause bearing system problems in the motor, directly leading to motor failure or even fatal inter-turn or overload .
● The operating conditions of the motor. This is an issue that must be considered in the early stage of motor design. Calculate the operating temperature of the motor according to the high temperature environment . For motors in plateau environments, the actual motor temperature rise is higher than the test temperature rise value.
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