Research On The Intelligent Protection Technique Of Overload Relay

As an important part in the traction system, the electric motor, which transfers the mechanical energy to the electrical energy, plays a crucial part in civilian economy. The abnormal operation of the motor affects the continuity of the production progress, resulting in severe loss. Hence, the significance of assuring the normal operation of motors pops up.With booming in new technology and increasing in complexity of the power system in industry, low-voltage electrical apparatus is able to develop in a electronic, intelligent, organized, modularized, high-quality and minimized way. Overload-protection relays belong to the generic protective electrical apparatus. When false occurs in electric motor, the overload-protection relays act rapidly and reliably to protect the electric motor. Hence, the intelligent technique of overload- protection has become the trend of development of electric motor protect, having far-reach impact on the industrial production in the future.This paper has a study on the intelligent technique of overload-protection relay. The protection principle of electric motor has been studied in theory. The related mathematical model and protection functions have been built concerning the overload, phase-loss, over-voltage and under-voltage of three-phase synchronous motor. The overload protection functions are achieved by calculating the heat accumulation inside the motor, considering the heat production and heat removal. Based on the protection principle of three-phase asynchronous motor, the hardware and software system of the intelligent overload-protection relays are designed with microprocessor PIC18F458 as the core .The real-time false inspection and effective protection of electric motor have been realized.