Research On Thermal Characteristics Of Motor And Development Of Thermal Protector With Single-Chip

During operating, the insulation properties of motors will decrease due to over temperature of stator winding, thus thermal protectors are needed in order to protect motor. With the development of microcomputer and electronics as well as information processing technique, motor protectors with single-chip have came forth, and been favored increasingly by users.In order to develop motor protectors with single-chip, it is important to research a reasonable overload protection model. In this paper, a 2.2 kW motor is used for researching thermal property. 6 thermistors are encased in stator winding, thus the temperature of stator winding can be measured. The automatic measure device with microcomputer is designed. The heating and cooling process are measured by means of the above device. The experimental results are compared with the existing criterion and model so as to obtain the optimal overload protection model, viz. exponential heating and cooling equations, which can be used for protecting motors.Based on the selected overload protection model, a thermal protector with single-chip is designed in this paper. The protector uses PIC16F873 single-chip as the center, adds measuring circuit and interface circuit etc. And the protector has the features of small volume and high reliability as well as multi-functions such as setting parameters and displaying status and diagnosing faults so on. According to the operation condition, it is shown that the protector presented in this paper can duly follow the motor's load fluctuation and capitally match with motor's tolerance overload characteristic, thus it is valuable to be actually used.