Research And Realization Of Electric Heating Intelligent Motor Protection Method

The stable operation of the motor is an important guarantee for the development of the domestic economy,so it is of great realistic significance to study high-reliability motor protection devices.However,current motor protection devices mostly use current transformers that are easy to saturate as current measuring devices.When the overload multiple is high,it is easy to cause the distortion of the secondary side current,so the electronic development of the protector is restricted.Since there is no saturation phenomenon in the current heating effect,and in order to optimize the current measurement method,enlarge the measurement confines,and improve the reliability,this thesis proposes an electric heating intelligent motor protection method based on the current heating effect.This subject comes from the National Natural Science Foundation of China: Research on the key issues of the new thermo-electromagnetic hybrid release and the selective protection of circuit breakers(project number: 51777129).First of all,this thesis discusses the electrothermal current measurement method.Researching the use of a measuring cavity to collect temperature signals,and according to the principle of heat balance,a mathematical model between the stable temperature rise of the thermal element and the current is established.The measurement cavity takes a long time to reach the stable temperature rise.In order to quickly measure the effective value of the current,a recursive algorithm for quickly solving the steady-state temperature rise is proposed and verified by simulation.Additionally,this thesis uses COMSOL simulation software to perform multi-physics simulation of the measurement system,and solves the unknown parameters in the recursive algorithm by processing the simulation results.The overload,open phase and ground fault of three-phase asynchronous motor are simulated by Simulink.The corresponding fault criteria and protection measures are given by analyzing the changes of stator current under different faults.Then,the thesis designs hardware circuits,such as the minimum system,analog acquisition and processing module,man-machine interaction module,protection module and communication module.The software part adopts modular programming method,and designs signal acquisition and processing subroutines,protection subroutines,man-computer interaction subroutines and communication subroutines.Through RS-485 bus based on Modbus RTU protocol,the communication between upper computer and lower computer is built,and the host computer monitoring interface based on MATLAB GUI is designed.Finally,a prototype of an electrothermal intelligent motor protector was made and an experimental platform was built.Three tests were carried out using the experimental equipment,including the verification of the electrothermal current measurement method,the motor overload experiment and the unbalance experiment.By processing the test results,it is verified that the electrothermal intelligent motor protection method can monitor and protect the motor in real time.