“Temperature rise” is an important parameter to measure and evaluate the degree of heating of the motor, which is measured under the thermal balance state of the motor at rated load. End customers perceive the quality of the motor. The usual practice is to touch the motor to see how the temperature of the casing is. Although it is not accurate, it generally has a pulse on the temperature rise of the motor.
When the motor fails, the most significant initial feature is the abnormal temperature rise of the “feel”: the “temperature rise” suddenly increases or exceeds the normal operating temperature. At this time, if measures can be taken in time, at least major property losses can be avoided, and even a disaster can be avoided.
The temperature rise is the difference between the working temperature of the motor and the ambient temperature, which is caused by the heat generated when the motor is running. The iron core of the motor in operation will generate iron loss in the alternating magnetic field, copper loss will occur after the winding is energized, and other stray losses, etc., will increase the temperature of the motor.
When the motor heats up, it also dissipates heat. When the heat generation and heat dissipation are equal, the equilibrium state is reached, and the temperature no longer rises and stabilizes at a level, which is what we often call thermal stability.
When the heat generation increases or the heat dissipation decreases, the balance will be broken, the temperature will continue to rise, and the temperature difference will be expanded. We must take 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, so the temperature rise is an important indicator in the design and operation of the motor, which indicates the degree of heat generation of the motor. During 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.
The relationship between temperature rise and temperature and other factors
For a motor in normal operation, theoretically, its temperature rise under rated load should have nothing to do with the ambient temperature, but in fact it is still related to factors such as ambient temperature and altitude.
When the temperature drops, the copper consumption will decrease due to the decrease in the winding resistance, so the temperature rise of the normal motor will decrease slightly.
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 winding copper losses increase as the air temperature rises. Therefore, temperature changes have a greater impact on large motors and closed motors, and both motor designers and users should be aware of this problem.
For every 10% increase in air humidity, the temperature rise can be reduced by 0.07~0.4°C due to improved thermal conductivity. When the air humidity increases, another problem arises, that is, the problem of moisture resistance when the motor is not running. For a warm environment, we must take measures to prevent the motor winding from getting wet, and design and maintain it according to the humid tropical environment.
When the motor runs in a high-altitude environment, the altitude is 1000m, and the temperature rise increases by 1% of its limit value for every 100m per liter. This problem is a problem that designers must consider. The temperature rise value of the type test cannot fully represent the actual operating state. That is to say, for the motor in the plateau environment, the index margin should be appropriately increased through the accumulation of actual data.
temperature rise and temperature
For motor manufacturers, they pay more attention to the temperature rise of the motor, but for the end customers of the motor, they pay more attention to the temperature of the motor; a good motor product should take into account the temperature rise and temperature at the same time to ensure that the performance indicators and life of the motor meet the Require.
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 point temperature and a reference temperature. The difference between the temperature of a certain part of the motor and the surrounding medium is called the temperature rise of this part of the motor; the temperature rise is a relative value.
Within the allowable range and its grade, that is, the heat resistance grade of the motor. If this limit is exceeded, the life of the insulating material will be shortened sharply, and it will even burn out. This temperature limit is called the allowable temperature of the insulating material.
Motor temperature rise limit
When the motor runs under the rated load for a long time and reaches a thermally stable state, the maximum allowable limit of the temperature rise of each part 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 related factors should be considered comprehensively.
When the motor is running under load, it is necessary to play its role as much as possible, that is, the larger the output power, the better (if the mechanical strength is not considered). But the greater the output power, the greater the power loss, and the higher the motor temperature. We know that the weakest thing in the motor 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 properties of insulating materials are very stable, and their working life is generally about 20 years.
Insulation class indicates the highest allowable operating temperature class of the insulating structure, at which temperature the motor can maintain its performance for a predetermined period of use.
The limit working temperature of the insulating material refers to the temperature of the hottest spot in the winding insulation during operation of the motor during the design life expectancy. According to experience, in actual circumstances, 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 is close to or exceeds the extreme operating temperature of the material for a long time, the aging of the insulation will be accelerated and the lifespan will be greatly shortened.
Therefore, when the motor is in operation, the operating temperature is the main and key factor in its life. That is to say, while paying attention to the temperature rise index of the motor, the actual operating conditions of the motor should be fully considered, and sufficient design margin should be reserved according to the severity of the operating conditions.
The comprehensive application entity of motor magnet wire, insulating material and insulating structure 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 index of the motor, which comprehensively reflects the safe operation performance and design and manufacturing level of the motor.
In the design of the motor scheme, the primary consideration is what kind of insulation system to use, whether the insulation system matches the level of the factory’s process equipment, and whether it is ahead or behind in the industry. It should be emphasized that it is most important to do what you can. Otherwise, if the level of technology and equipment cannot be reached, you will pursue the leading position. No matter how advanced the insulation system is, you will not be able to manufacture a motor with reliable insulation performance.
We must take into account these issues
Compliance with magnet wire selection. The selection of the motor magnet wire should match the insulation grade of the motor; for the variable frequency speed regulating motor, the influence of corona on the motor should also be considered. Practical experience has confirmed that the thick paint film motor wire can moderately accommodate some effects of motor temperature and temperature rise, but the heat resistance level of the magnet wire is more important. This is a common problem that many designers are prone to delusion.
The choice of composite material must be strictly controlled. During the inspection of a motor factory, it was found that due to the shortage of materials, the production workers would substitute materials lower than the requirements of the drawings.
effects 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 high, 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. With the loss and failure of grease, the motor is prone to bearing system problems, which directly lead to motor failure, or even fatal inter-turn or overload.
The operating conditions of the motor. It is a problem that must be considered in the early stage of motor design. The operating temperature of the motor is calculated according to the high temperature environment. For the motor in the plateau environment, the actual motor temperature rise is higher than the test temperature rise.
Post time:
Jul-11-2022