What is the measurement method of the internal temperature of the shaft motor shell?
1. Thermometer method: this method uses a thermometer to directly measure the temperature, which is the most simple. However, the thermometer can only touch the surface of each part of the motor; the measured temperature is only the surface temperature. The maximum temperature inside the motor cannot be measured with a thermometer.
Resistance method: this method can only be used to measure the average temperature of the winding. The principle is as follows.
Before the motor runs, we first measure the cold resistance R1 of the winding, that is, the resistance when the winding temperature is equal to the cooling medium temperature T1. When the humidity of the winding increases to T2, the resistance of the winding increases to R2. If the temperature is measured in centigrade, there is the following relationship for the copper winding: R1 / r2 = (235 + T1) / (235 + T2). From the above formula, if R1, R2 and T1 are known, T2 can be solved. T1-T2 is the temperature rise of the winding to the cooling medium. For the sub aluminum wire winding, the constant 235 in the above formula is changed to 225.
Superposition method (double bridge live temperature measurement method): without interrupting the alternating load current, a weak DC current is superimposed on the load current to measure the change of DC resistance of the winding with the temperature so as to determine the temperature rise of the AC winding. The temperature rise limit of each part of the motor is related to the grade of the used rubber material, the temperature of the cooling medium and the method of measuring the temperature. The life of insulating material depends on its absolute temperature when it travels far away, not on its temperature rise. From winter to summer, from north to south, the ambient temperature changes a lot. When the ambient temperature is low, the temperature rise limit of the motor can be increased, but when the ambient temperature is high, the temperature rise limit of the motor must be reduced. For the sake of clarity, when the temperature rise limit of each part of the motor is specified, the standard temperature of the cooling medium must be specified at the same time. The standard temperature of cooling medium is 4q ℃. According to this regulation, the temperature rise of each part of the motor, using different insulating materials and using different temperature measurement methods, has different temperature rise limits.
Embedded thermometers: for motors with large rotating shafts, embedded thermometers are often installed at the points where higher temperature may be estimated during assembly. Temperature detecting elements include thermocouple and resistance thermometer, etc. The heating end of the thermometer can be buried in the depth of the groove, for example, between the conductor and the horizontal bottom, between the upper and lower conductors. The outgoing end of the thermometer is led to the outside and connected to the measuring instrument to read the temperature. The more thermometers are used, the more likely the temperature is to be close to the hottest spot.