Research And Implementation Of Intelligent Protection Strategy For Small Power Distribution System

With the development and progress of intelligent technology of distribution network,the intelligentization of low-voltage distribution appliances has become the key to the construction of intelligent distribution network.Faults such as short circuit and overload in the terminal power distribution system are inevitable.Therefore,only low-voltage circuit breakers can be required to cut off the circuit faster and more accurately when a fault occurs,so as to shorten the fault time and reduce the scope of power outages.At present,the requirement for intelligent distribution network is to achieve full selective protection,and the three-stage current protection of traditional circuit breakers can no longer meet this requirement.For the short-circuit protection problem,the existing Zone Selective Interlocking（ZSI）protection technology can be used to solve the problem,but when the lower-level circuit breaker has an overload fault,the selective protection problem still cannot be solved.Based on the National Natural Science Foundation of China: Key Issues of New Thermo-Electromagnetic Hybrid Releases and Networked Selective Protection of Circuit Breakers（Project No.51777129）,this paper proposes a new method to realize fully selective protection of power distribution systems.Protection strategy combined with Zone Selective Interlocking Protection technology and Dupline bus communication.First of all,in view of the over-tripping of the upper circuit breaker and the refusal of the lower circuit breaker that may occur in the traditional three-stage current protection technology,a three-stage protection of circuit breakers under overload and short circuit conditions based on the principle of Zone Selective Interlocking Protection is proposed.The principle of matching characteristics.Then a protection strategy of intelligent power distribution system is proposed,in which communication function is added to achieve signal transmission between upper and lower circuit breakers.In addition,MATLAB/Simulink is used to build the short-circuit and overload model of the low-voltage power distribution network,and the current changes during overload and short-circuit faults are simulated,as well as the traditional three-stage current protection and the anti-malfunction and anti-actuation protection based on the ZSI principle.Secondly,according to the protection requirements,the hardware design of the intelligent circuit breaker controller network is completed.This design takes STM32F103 series single chip microcomputer as the core of the intelligent circuit breaker controller,including the power input module,voltage and current measurement module,trip drive module,human-computer interaction module and Dupline bus communication circuit.Finally,based on the hardware circuit design and the proposed control strategy,the software program is designed,including the main program,the sampling program,the intelligent three-stage protection program,the voltage and temperature protection program,and the button program.Through the cooperation of software programs and hardware circuits,the fully selective protection of the intelligent power distribution system is completed.