Research On Design Of Releasers Of Intelligent Circuit-breakers

Abstract： Low-voltage circuit-breakers are important protection and controlapparatus in electricity grid, used to open and shut, bear the normal, overloaded, andshort circuit current. Of all parts of circuit-breakers, releasers are the core, whichprovide current-protection function and other kinds of functions. With developmentof microcomputer technology, power electronics technology and networkcommunication technology, releasers develop into intelligent models fromthermoelectric and electromagnetic models, which take microcomputers as core partsand can communicate through network. The emergence and application of intelligentreleasers is a milestone in circuit-breakers’ history.In this project, an intelligent releaser with a Renesas R8C/23MCU is designed.This releaser applies quasi-synchronous sampling algorithm to calculate RMS valueof current and CAN-bus to communicate with host computer or other nodes. Thereleaser can realize overload-protection (a long time delay), short circuit protection (ashort time delay) and instantaneous protection. And the releaser has a reliable settinginterface, which asures that it has excellent performance and is used widely.The intelligent releaser has7parts: the main control unit (with a R5F2123AJFPof Renesas R8C/23), the AC sampling and a two-channel signal amplifier unit, theparameters setting unit, the self-generated power unit, the trip-driver unit, thecalendar and the temperature-protection unit and CAN-bus communication unit.In the research, mathematical models of long-time delay protection, short-timedelay protection and instantaneous protection are established. Quasi-synchronoussampling algorithm is applied to calculate the RMS value of current, and through this,synchronization error impact is eliminated, and signal offset margin improved.High-performance Embedded Workshop of Renesas Enterprise is applied to code anddebug in.R5F2123AJFP has a CAN module in it, with that the releaser can communicatewith host computer and other circuit-breakers. CAN-bus has excellent EMI capability, a high speed of information transmission, predominant toplogy and frame structure.It’s simple to finish networking with CAN-bus which used more and more widely.In the design of hardware and software, electromagnetic compatibility isconsidered, and kinds of anti-jamming methods are applied. The results show that thereleaser has a good overall performance, and the intended purpose achieved.