Study On Electromagnetic System And Motion Characteristic Of Two-stage Short Circuit Disconnection

With the development of science and technology,the research and development of smart grid and the construction of smart grid science and technology are also increasingly sophisticated,which conflicts with the current and time setting problems,so it is necessary to improve the selectivity and rapidity of distribution system protection.In order to ensure the reliability and continuity of residential power consumption,circuit breakers other than the bottom circuit breaker usually need to have short circuit and short delay protection characteristics to achieve selective protection,otherwise instant power failure will cause great losses.Therefore,for the selective protection of low-voltage distribution system,the key is that the protection features of circuit breakers at all levels should be coordinated with each other,so as to expand the protection scope and realize protection from the beginning to the end,that is,from the power supply side down to the terminal.Interlocking(ZSI)technology is a kind of intelligent protection method commonly used in modern society.: one is achievable selectivity;the other is achieve speed.Obviously,it makes up for the deficiency of current and time setting.Now the problem is how to make the distribution system without intelligent small circuit breaker has a certain intelligent function,which requires it to have a two-phase short circuit trip electromagnetic system.Based on the principle of ac electromagnet short circuit ring,a new MCB structure is innovated in this thesis.The small MCB is improved from the two directions of full selective protection and intellectualization,so as to realize two-phase short circuit protection.The principle is based on ac electromagnet short circuit ring demagnetization.Ac electromagnet are in a normal working state,when near an alternating current is close to zero,current is small,can cause electromagnetic suction is smaller,then there will be a core vibration phenomenon,in order to avoid this kind of situation can install a core pole face ventilation with alternating current(ac)will have the role of magnetic magnetic ring,its role in concrete under the condition of invariable when the excitation magnetic potential,the magnetic flux in magneticcircuit is reduced,or when the same magnetic flux demand more exciting magnetic potential.Then the feasibility of the principle is verified by experiments,which opens up a new way for the small circuit breaker to realize the two-stage short circuit trip of the electromagnetic system.In this thesis,the miniature circuit breaker dz47-60 as the reference,research the structure and motion characteristics,master the miniature circuit breaker movement mechanism;Familiar with ZSI working principle;A new type of electromagnetic system which can realize two-phase short-circuit trip is proposed.The electromagnet was selected as U type,and the main influencing factors of tripping current were analyzed by maxwell equation theory.Matlab simulink as the application software to verify the theoretical derivation of the factors;Design electromagnetic mechanism;Ansoft software was used to model and simulate the 3D magnetic field.After obtaining the simulation results,the structure was further improved to make it close to the theoretical value.Finally,the new structure can be applied in miniature circuit breaker.In the design,the appropriate air gap and spring reaction should be considered,and the electromagnetic suction of key points should be selected.The research of electromagnetic system and action characteristic of two-phase short circuit tripping can be realized,which provides short circuit and short time delay protection.It is not only the basis of ZSI technology that can be used in distribution terminal,but also makes the application of full selective protection in distribution system have new possibility.