Research And Development Of Computer Control System For Over-Current Testing Of Frame Circuit Breaker

Frame circuit breaker is a protection component widely used in low-voltage power distribution backbone. It is crucial for the safe and reliable of low voltage power distribution network. The circuit breaker products should be tested and verified in factory examination to ensure the product reliability. The reliability of circuit breaker involves specifications in many aspects, the protection characteristic reliability under high practical current is one of key technical indices. In recent years, some high current automatic test systems based on computer have been developed for the test of circuit breaker reliability, which improve the automatic level of breaker reliability test equipment remarkably. Most of these equipments largely adopt analog way to generate current, which usually has problems of non-standard and low efficiency. Aimed at these shortcomings, a computer test system based on industrial control computer and PLC is developed for the high current test of frame circuit breaker. With dedicated fixture and current generation and switching device,it can accomplish all of predetermined testing items including long-delay protection test, ground protection test and data communication protocol test automatically. Such a system is suitable for the frame circuit breakers whose rated current ranges from 400A to 4000A.The realizations of the hardware and software for high current test system have been detailed in this paper. Furthermore,in order to improve the efficiency, and make the output current of the adjustable high current source reaches the target value through once automatic modulation. Curve fitting has been used to obtain the trend of the secondary side open-circuit voltage of regulator and the current value of transformer. Thus realize the prediction of regulator's secondary side voltage by analyzing the results and improving the fitting model.Facing the rapid development of information technology, the frame circuit breaker mostly use intelligent digital controller. Another automatic test system based on the high current test platform is developed for the communication reliability test of intelligent controller. Such system can be used to test the remote signaling, remote adjustment, remote measurement and remote control functions of universal circuit breakers based on the Modbus protocol through RS-485 interface. During the testing process, a testing current supplied by an adjustable high current source is fed into the primary circuits of tested breaker to simulate the actual operation situation of circuit breaker. This makes the testing results more credible and reliable.Compared with present test methods and equipments, the system has some merits such as high automation, standardization, efficiency and generality. Such a system has been put into trial run in the universal circuit breaker assembly line of Hangzhou Zhijiang Switchgear Stock Co. Ltd and operates well in practice.