Research On HV Motor Protection Under Variable Frequency Operation State

With a growing shortage of energy in the world today, energy efficiency gradually becomes the subject of the power system. High-voltage inverter for its superior energy-saving and adjustment feathers attracts people's attention, and has been widely used. With the vigorous development of the power system, the requirements for the safety of high-voltage electric motor become higher and higher. The safety for the motor is mainly granted by relay protection. However, the traditional, high-voltage frequency motor protection can not be applied to the variable-frequency operation state. By researching a suitable frequency high voltage motor protection, this problem can be solved.In this paper, according to the principle of the power system relay protection, the micro computer relay protection principle and the power system fault analysis technology and algorithm are investigated. With the power frequency runtime relay protection research as the starting point, the high voltage motor fault condition in the variable-frequency operation state and how to config its relay protection are researched. On the basis of theoretical study and using the MATLAB/SIMULINK simulation technology, the power frequency and variable-frequency of motor fault simulation model was set up. Based on the research of the output waveform, the scheme for the relay protection under the variable-frequency running condition is considered. A set of broadband sampling CT for current measurement of variable-frequency operation condition was installed in the end of the frequency converter. When running under the variable-frequency state, low voltage electric motor protection, over-voltage protection, overload protection and too long time starting can be cancelled. Longitudinal differential protection, current instantaneous fault protection, motor ground protection, negative sequence current protection, and locked-rotor protection can be set according to meeting the protection requirements of high voltage motor.Based on the above conclusions, the field application test was done, and the test results show that the conclusion on the relay protection of variable frequency motor is effective.