Study On The Protector Of Motor Based On Thermal Model

The motor protections have been studied for a long time. Recently, as the advance of electronics and microcomputer, microprocessor-based motor protections have developed a lot. But the motor protectors based on inverse time-current characteristic curve can't protect motor effectively during the cold condition overload and hot condition overload and many of them have similar functions with the electromechanical or electronic protector. Many powerful functions of the computer, such as numerical calculation, data storage and logical decision, are not be used properly. Moreover, most of present microprocessor-based motor protectors only run individually, which can't realize the Ethernet measurement and control.On the basis of analyzing the thermal circuit model of motor, an available method for building thermal model of motor is presented in this thesis. The thermal model of a 10kW prototype machine and its discrete recursion algorithm for calculating temperature rise online is also deduced. By means of the discrete algorithm, the temperature rise of the stator windings can be calculated in real time, which is the reference variable for motor protection, and the reliable protection of motor can be realized during the cold condition overload or hot condition overload.With the MATLAB, a software package, the simulation of temperature rise for the lOkW prototype machine has been down during the motor starting and running under the varying load condition. The overload characters of the motor have been drawn under the different load ratio. The simulation result demonstrated that the cold condition overload or hot condition overload can be distinguished by the discrete recursion algorithm for calculating temperature rise online.The hardware of the protector based on thermal model has been designed with the C8051F020 single-chip computer produced by CYGNAL Co. in the thesis. The dot matrix LCD is used as display device to display Chinese menu in order to set motor parameter or display the motor parameter and the temperature rise. In addition, the conceiving for browsingand controlling the status of motor protector with Internet Explorer by means of TCP/IP protocol are realized using the single chip computer and he network controller. The software design and the anti-interference methods are also introduced.