Research On Critical Technologies Of Electromechanical Hybird DC Circuit Breakers

In order to resolve contradictions that energy production facilities are far away from load concentrated areas and to satisfy the requirements of clean energy grid-connected power generation and update of urban distribution network,the technology of direct current transmission（distribution）has been the focus of electric power departments of varieties of countries.In terms of long-distance power transmission,interconnection of distributed energy and urban electricity supply,HVDC owns incomparable advantages compared to conventional alternating current transmission.As a significant component to guarantee stable and secured operation of DC system,it gets to be difficult for DC circuit-breaker to keep the pace with development trend of multi-terminal,high-voltage and large-capacity DC electric power network.So the development of DC electric power network with high-performance has been a guarantee for the continuous development of HVDC.On the basis of consulting a large number of relevant literatures,this paper demonstrates research background of hybrid electro-mechanical DC circuit breaker.It also analyzes breaking principle,strengths and weaknesses as well as research situation at home and abroad of current mechanical,all solid state and hybrid DC circuit breakers.Based on existing problems of current hybrid DC circuit breaker and requirements of DC electric power network for DC circuit breakers,a kind of hybrid electro-mechanical DC circuit breaker model with long working lifespan,high reliability,less conduction losses and bidirectional breaking ability is put forward.The novel hybrid electro-mechanical DC circuit breaker mentioned here adopts a combining method of natural commutation and forced commutation to realize transmission of DC power so as to break DC current.Core process of topology plan in this paper is to make use of transmission process of arc voltage activation energy.In order to simulate the natural converter process,it is necessary to model the DC arc mathematically.In this paper,Cassie model,Mayr model and KEMA model are briefly presented,their application scopes are analyzed and a model of arc dual-route model is introduced to obtain parameters in arc model.Topology structure of novel hybrid electro-mechanical DC circuit breaker is designed.In comparison with current hybrid DC circuit breaker,topology plan mentioned in this paper not only ensure breaking ability,but also reduce conduction losses of circuit breaker so that working lifespan of these circuit breakers are ensured.And it also comes up with topology structure and working principles of capacitive resistor and solid state switching commutation branch,summarizes key components that could improve integral performance of circuit breaking and proposes methods to calculate capacitance value in capacitive resistor commutation branch.And then action sequence together with variation of voltage and current in capacitive resistor commutation and solid state switching commutation based hybrid circuit breaking are analyzed.Under the environment of MATLAB/Simulink,the simulation of145k V/8000A DC current breaking of SF₆ circuit breaking based hybrid circuit breaking is carried out to verify effectiveness of energy transmission and shortened effectiveness of arcing time in both capacitive resistor commutation branch and solid state switching commutation branch,and to implement simulations on their whole processes of breaking DC current.At last,scaled-down laboratory principled sample machine for topology structure of commutation branch in proposed novel hybrid DC circuit breaking is established in laboratory.Through scaled-down experiments,two kinds of commutation branch topology structure are verified experimentally.Simulation and experimental results show that hybrid circuit breaking designed with topology mentioned in this paper gets the characteristics of lower conduction loss and higher reliability.It reduces the difficulties of breaking DC current and limits arcing time of DC electric arc to a fairly low level,which effectively contributes to ensured long-lasting working lifespan of the whole machine and provide it with bidirectional breaking ability.