At what temperature does the motor overheat and get damaged?

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This post was last edited by wangshaobo on 2025-6-19 at 12:55. At what temperature does a motor get damaged? The temperature limits for various parts of a motor are as follows: 1. The temperature rise of the core in contact with the windings (using the thermometer method) should not exceed the temperature rise limit of the insulation of those windings (using the resistance method). Specifically, for class A, this limit is 60°C, for class E it is 75°C, for class B it is 80°C, for class F it is 100°C, and for class H it is 125°C. 2. The temperature of rolling bearings should not exceed 95°C, while the temperature of sliding bearings should not exceed 80°C. High temperatures can cause changes in the oil quality and damage the oil film. 3. In practice, the casing temperature is generally considered acceptable as long as it’s not hot to the touch. 4. The stray losses on the surface of the squirrel-cage rotor are high, resulting in high temperatures; this is generally kept within limits that do not pose a risk to the adjacent insulation. It can be estimated by applying irreversible color-changing paint in advance. The temperature and temperature rise of a motor are used to measure the degree of heat generation in the motor; it is the \"temperature rise\" rather than the \"temperature\" that is considered. When the temperature rise increases suddenly or exceeds the maximum operating temperature, it indicates that the motor has failed. The following discusses some basic concepts. 1. Insulation class of insulating materials: Insulating materials are classified into 7 grades, Y, A, E, B, F, H, and C, based on their heat resistance. Their maximum operating temperatures are 90°C, 105°C, 120°C, 130°C, 155°C, 180°C, and above 180°C respectively. Performance reference temperature (°C): A80, E95, B100, F120, H145. Insulation materials can be classified into the following 7 grades based on their thermal stability: 1. Grade Y, 90 degrees, cotton; 2. Grade A, 105 degrees; 3. Grade E, 120 degrees; 4. Grade B, 130 degrees, mica; 5. Grade F, 155 degrees, epoxy resin; 6. Grade H, 180 degrees, silicone rubber; 7. Grade C, above 180 degrees. In commonly used Grade B motors, the insulation material inside is usually of Grade F, while the copper wires may be of Grade H or even higher to improve their quality. Generally, to extend the service life, higher insulation requirements are specified, with assessments conducted at a lower level. For example, oil pump motors with common Class F insulation are evaluated according to Class B standards; that is, their temperature rise must not exceed 120 degrees (with 10 degrees reserved as a margin to prevent individual motors from having a temperature rise that exceeds the specified limit due to process instability). The so-called maximum operating temperature of insulating materials refers to the temperature at the hottest point in the winding insulation during operation, over the expected service life of the motor. Based on experience, grade A materials can have a service life of 10 years at 105°C, while grade B materials can achieve a 10-year lifespan at 130°C. However, in practice, both the ambient temperature and temperature rise do not remain at their design values for extended periods; therefore, the typical service life is between 15 and 20 years. If the operating temperature exceeds the material’s maximum operating temperature for an extended period, insulation aging accelerates, significantly reducing its lifespan. Therefore, during operation, temperature is one of the main factors affecting the lifespan of the motor. The insulation class of a motor refers to the heat resistance rating of the insulating materials used, and is classified into grades A, E, B, F, and H. The allowable temperature rise refers to the limit of the increase in the motor’s temperature compared to the ambient temperature. In electrical equipment such as generators, insulating materials are the weakest link. Insulating materials are particularly susceptible to the effects of high temperatures, which accelerate their aging and cause damage. Different insulating materials have varying heat resistance, and electrical equipment made from these materials has different capacities to withstand high temperatures. Therefore, general electrical equipment has a specified maximum operating temperature.