ABSTRACT :The low-voltage breaker is a kind of switch electrical appliance .It can get-on and cut the distribution circuit and protect all kinds of faults. It can be widely used in the low-voltage distribution system. The releaser executes the function of breaker. The traditional releasers always are electromagnetic and it is not easy to control their trait. The task uses the microelectronics technology and single-chip technology and utilizes microprocessor to develop the mini-intelligence releaser. It can not only fulfill the function of releasing, i.e. fulfill the protecting function which is pre-designed, but also select the parameters of motion, i.e. it can realize protecting in the multi-situations. By using the system, the target of remote controlling is realized .All of them strengthen the releaser's functions and make it accord with requirements of distribution system. The basic principles of the design are accounted detail,the selective bases and the operational principle of the hardware are introduced chiefly and the design reasons and program means of the software are recommend in this thesis.
KEYWORDS: breaker, releaser, true-rms.