Research On Real-time Monitoring Technique For Protection Performance Of Overload Relay

Overload relay is a kind of protection low-voltage apparatus, which is widely used inelectric power system. It is generally used together with the contactor to realize the faultprotection of motor and other electrical equipment. According to incomplete statistics,more than20,0000motors are burned down every year. One of the main reasons is that theprotection performance and the reliability of the overload relay decrease. Nowadays theresearch on the protection performance of overload relay is focused on improvement ofprotection method, processing technology and material properties, etc.. The performance ofthe various components will degrade constantly with the use of the overload relay, but theresearch on the change of performance state is limited. It is necessary to monitor thechange of protection performance of overload relay to realize the state assessment and itwill become an important research topic.In this paper, the theoretical analysis on energy conversion principle of the thermalbimetal system of overload relay is carried out, and the parameters of the protectionperformance are determined. The hardware and the software of the real-time monitoringsystem are designed with PIC microcontroller as the core. The hardware system includesthe temperature and strain acquisition circuit, the clock circuit, the display circuit, thepower protection circuit, and so on. And the software system is designed with C languageto realize the functions such as data acquisition, display and storage. The communicationbetween PC and MCU is realized with RS232module. In addition, the anti-jamming designof the hardware system and the software system is finished. The monitoring tests are rununder the condition of different products, different initial temperatures, different points anddifferent multiples of the setting current. The test results and the theoretical results arecompared and analyzed. The change rules of the temperature, the strain and between themare found out. It will establish a good foundation to improve the performance and reliabilityof the overload relay.