Research On Electromagnetic Tripping System And Control Method Of Two-stage Short Circuit Protection

With the introduction of the concept of "smart grid",achieving reliability,safety,economy and efficiency of the grid has become a global goal.For the majority of users,the most important goal of achieving a smart grid is to ensure the reliability and continuity of electrical circuits and household appliances.As the most widely used small circuit breaker in terminal power distribution devices,it is favored by more people.As the core device of the miniature circuit breaker,the electromagnetic tripping device is one of the key factors restricting the intelligence of the miniature circuit breaker.Therefore,promoting the intelligent development of tripping device can greatly promote the intelligent development of small circuit breakers.The short-circuit protection of the traditional electromagnetic tripping device can only achieve instantaneous protection,without delay characteristics,which is not conducive to the selective protection of power supply and distribution.Aiming at this problem,this paper studies the intelligent structure of electromagnetic tripping device and its control method.The main works of this paper including the following aspects.First,a new structure of a dual-coil controllable electromagnetic tripping system is proposed.According to the principle of short-circuit demagnetization ring,the dual-coil electromagnetic system is used to replace the traditional single-coil electromagnetic system,so that the dual-coil electromagnetic tripping device has current two-stage short-circuit protection.The structure and working principle of the new electromagnetic system are explained,and its protection characteristics are compared with the traditional electromagnetic tripping system.The results prove the superiority of the new system.Secondly,the influencing factors of the minimum tripping current of the dual-coil controllable electromagnetic system are explored.The size of the air gap,the size of the core cross-sectional area and the number of turns of the secondary coil are the main factors that affect the current tripping of the dual coil electromagnetic system.Finally,the structure and related parameters of the dual-coil controllable electromagnetic tripping system were designed and calculated.A three-dimensional model was established using the finite element method.By controlling the open and short circuits of the secondary coil,the electromagnetic force and magnetic induction intensity were compared and analyzed.The simulation results verify the feasibility of the new structure.The structure has been modified on this basis.The modified structure is also feasible but compared with the former,the first proposed structure is more advantageous.The proposed dual-coil controllable electromagnetic tripping device is beneficial to achieve two-stage short-circuit protection,improve the reliability of the line,and promote the intelligent development of small circuit breakers.