| With the development of economy and technology, the motor has become the most widely used power equipment in modern industry and agriculture system. The motor is easier than ever to burn down, mainly due to the rapid development of insulation technology for motor, the design not only need to increase the output, but also required to reduce the volume, heat capacity of the motor more and more small, the overload ability is more and more weak;Because of the exaltation of automation degree, requirements for motor often frequent starting,braking and inversion, so the device to the motor protection have higher requirements.In this thesis, asynchronous motor for the study, discusses the heating and cooling mechanism of asynchronous motor, and the motor thermal overload protection of existing models are analyzed, according to the current changes of this phenomenon with the variation of load and the voltage of the power grid is analyzed and studied, proposed the Kuta established motor heat accumulation dynamic mathematical model by using the two order Runge-classic. Compared with the existing motor overload protection model, this model can more accurately reflect the operation status of the change in the current of the motor. The device based on overload protection and also has the motor stall, open phase, three-phase current unbalance, thermal overload, long start time, voltage fault protection.This thesis is based on PIC16F877microcontroller as the core of hardware and software design of the system, the hardware system consists of a data acquisition circuit, keyboard display circuit and the execution circuit. Using the software system is a modular program design, modular programming is independent of each other, and universality etc. Procedures for the preparation of the use of the C language programming, C language for the organization of the module program, debugging and maintenance. In order to realize the motor running state monitoring and fault judgement and display function. |
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