What Is Rigid Insulation?

Insulation level refers to the heat resistance level of the insulating material used in the winding of the motor (or transformer). There are five types of insulation materials commonly used in motors and transformers: A, E, B, F, and H. The insulation material of each insulation class has corresponding limit allowable working temperature (the hottest temperature of the motor or transformer winding). When the motor or transformer is running, the temperature of the hottest point of the winding must not exceed the requirements in Table 6-1, otherwise it will cause accelerated aging of the insulation material and shorten the life of the motor or transformer; if the temperature exceeds the allowable value, the insulation will be damaged, causing the motor or the Transformer burned. ^[1]

The insulation level of a motor refers to the heat-resistant level of the insulation material used, which is divided into A, E, B, F, and H levels. Allowable temperature rise refers to the limit that the temperature of the motor rises compared to the ambient temperature.

Insulation temperature class A class E class B class F class H class.

Maximum allowable temperature () 105 120 130 155 180 Winding temperature limit (K) 60 75 80 100 125.

Performance reference temperature () 80 95 100 120 145 In electrical equipment such as generators, insulation materials are the weakest link. Insulating materials are particularly susceptible to high temperatures and accelerate aging and damage. Different insulation materials have different heat resistance, and electrical equipment with different insulation materials has different high-temperature resistance. Therefore, the general electrical equipment specifies the maximum operating temperature.

According to the ability of different insulation materials to withstand high temperatures, seven allowable maximum temperatures are specified for them, arranged according to the temperature: Y, A, E, B, F, H, and C. Their permissible operating temperatures are: 90, 105, 120, 130, 155, 180, and 180 ° C. Therefore, Class B insulation indicates that the insulation heat resistance temperature used by this generator is 130 ° C. The user should ensure that the generator insulation material does not exceed this temperature when the generator is working to ensure the normal operation of the generator. Insulation material with insulation class B is mainly made of mica, asbestos, glass fiber by organic glue or impregnation.

The insulation level of a motor refers to the heat resistance level of the insulation material used, which is divided into A level, E level, B level, F level, H level, C level, N level, and R level. allow

With the occurrence of motor failure, motor overheating generally occurs, and overheating is very detrimental to the insulation of the motor. The most sensitive part of the motor to the heating reaction is the insulation of the stator winding. Each insulation material can only withstand a certain temperature. Exceeding the temperature allowed by itself will accelerate the aging of the insulation and shorten the service life of the motor. Kind of accident. Therefore, the inspection, detection and protection of motor overheating faults are very important for reducing the accident rate, reducing accident losses and improving the economic efficiency of the enterprise.

1.Relationship between motor temperature rise and insulation level Due to the difference between the place where the motor is used and the ambient temperature, "temperature rise" is often used to indicate the actual heat resistance of the motor insulation material. The so-called temperature rise refers to the temperature of electrical equipment (including motors) above the environment. The rated temperature rise of the motor refers to the maximum allowable temperature rise of the motor winding at the specified ambient temperature (+ 40 ° C), which depends on the winding insulation level. The insulation level of a motor is a level that indicates that the insulation material used in the motor winding can withstand the temperature limit. The relationship between the maximum allowable temperature (rated temperature rise) of the motor and the insulation level is shown in Table 1. Rated temperature rise of the motor t0 = maximum allowable temperature of the motor t-ambient temperature t0, where t0 = + 40 ° C, t refers to the maximum allowable temperature of the motor windings. For the running motor, because the actual temperature of the winding cannot be measured directly, the external temperature of the casing (that is, the temperature in the eyelet hole) can only be measured indirectly, which is about 10 ° C lower than the hottest point of the motor winding. Therefore, the actual measured temperature of the casing plus a temperature difference of about 10 ° C is the maximum allowable temperature t of the motor. 2. The maximum allowable temperature rise of each part of the motor is shown in Table 2. 3. Method for measuring the temperature of the motor (1) Feeling method: that is, a method of estimating the temperature of the motor by touching the specified part of the motor with the hand and measuring the heat of the feel. See Table 3. (2) Thermometer method: The temperature rise of the motor is directly measured with a thermometer. When the motor reaches the rated operating state, its temperature also gradually rises to a certain stable value and no longer rises. At this time, the thermometer (preferably an alcohol thermometer) can be used to measure the temperature of the motor. The method is: the ball of the alcohol thermometer is wrapped with tin foil and inserted into the hole of the motor ring, so that the ball of the thermometer is closely attached to the periphery of the hole, and then the hole is tightly sealed with cotton. At this time, the temperature measured by the thermometer is about 10 ° C lower than the hottest point of the motor winding, so adding the measured temperature to 10 ° C and subtracting the ambient temperature (+ 40 ° C) is the actual temperature rise of the motor. Table 1 Relationship between motor temperature rise and insulation grade The maximum allowable temperature of insulation grade YAEBFHC 90 105 120 130 155 180> 180 Rated temperature rise 50 65 80 90 115 140> 140 (+ 40 ) Temperature rise limit of different insulation grades in parts name AEBFH Thermometer method Resistance method Thermometer method Resistance method Thermometer method Resistance method Thermometer method Resistance method Thermometer method Resistor windings Rotor winding 55 60 65 75 70 80 85 100 105 125 Stator core 60 75 80 100 125 Slip ring 60 70 80 90 100 Plain bearing 40 40 40 40 40 Rolling bearing 55 55 55 55 55 The temperature rise limit of the situation Table 3 The relationship between the surface temperature of the motor case and the feel of the case surface temperature Feeling description 30 Slightly colder than body temperature, feels slightly colder 40 Slightly warmer, feels warmer 45 When you touch it gently, you feel Warm 50 Slightly hot for a long time, touch the palms with red, 55 The heat can only be touched by hand 5 6s 60 More hot, only touched by hand 3 4s 65 Very hot, only touched by hand 2 3s, After leaving, the palm still feels hot 70 Very hot with one finger can only touch about 3s 75 Extremely hot Touch with one finger, can withstand 1 ~ 2s 80 Extremely hot, suspect that the motor has burned out, touch with one finger will not work, vinyl resin Curled from 85 to 90. It is extremely hot. If you suspect that the motor has burned out, if you touch it with your fingers, it is like it is burned. (3) Resistance method: Use the principle that the conductor resistance increases with increasing temperature to measure. As long as the cold and hot resistances of a certain phase winding of the motor are measured separately, the average temperature rise of the motor can be calculated t0 = t2-t0 = [(R2-R1) (235 + t1) / R1] + t1-t0 where t1 Cold state temperature of a certain phase of the motor, t2Temperature state of a certain phase of the motor, t0Ambient temperature, + 40 R1Cold state resistance of a certain phase of the motor, R2A phase of the motor Winding thermal resistance (must be measured within half a minute after the motor is powered off), 4. Causes of motor overheating failure (1) The motor is overloaded. Such as: fixed, friction between rotors (commonly known as rifling), unqualified assembly, overloaded mechanical failures such as friction or card stuck. (2) The motor is running out of phase. (3) The imbalance of the three-phase voltage and three-phase current exceeds the allowable range. (4) The power supply voltage is too high or too low, exceeding the allowable range of the motor's rated voltage (ie, ± 10%). (5) The wiring of the motor winding is incorrect. For example: the stator terminal of a certain phase is connected in reverse. (6) The motor winding is faulty. Such as: short-circuit between winding turns or layers, winding grounding. (7) The insulation between the stator core silicon steel sheets is damaged, so that the stator core is short-circuited, causing the stator core eddy current to increase and causing the motor to overheat. (8) Frequent startup. (9) The air duct of the motor is blocked and the ventilation is poor. (10) The ambient temperature of the motor is too high (+ 40 ° C beyond the design requirements), the heat dissipation is poor, and the cooling effect is poor.

According to GB 755-2008, the temperature rise limit of windings under Class F insulation should be 105K, not 100K. Generally, the insulation level of motors is E-level and B-level insulation.