Interruption Ability In The Novel Mechanical Medium Voltage DC Circuit Breakers

With the access of distributed new energy power generation system and increase of load and electricity demand diversification,the advantages of DC distribution network,such as big power supply capacity,small circuit loss,high power quality and flexible and convenient access of renewable energy,are increasingly obvious.It is the general trend to develop DC transmission and distribution technology.As an indispensable control and protection element in DC distribution network,the lack of commercial DC circuit breakers which have low cost and large capacity is the primary problem in the development of DC transmission and distribution technology.Therefore,developing a low cost and practical medium voltage DC circuit breaker which can break DC fault current safely and quickly have great significance.A novel type of mechanical medium voltage DC circuit breaker based on ‘zerovoltage' principle has been proposed.The working principle and process are analyzed.In the novel mechanical medium voltage DC circuit breaker,the continuous diode can create ‘zero–voltage' time for the main switch to improve its dynamic dielectric recovery strength.The simulation model of the novel mechanical medium voltage DC circuit breaker and simulation circuit are set up in an electro-magnetic transient state simulation software which named ATP-EMTP.The parameter range of the reverse oscillation branch,regulation rule of ‘zero-voltage' time,breaking capacity of the novel mechanical medium voltage DC circuit breaker in small contacts gap are analyzed.The simulation results shows that ‘zero-voltage' time range from 0 to 359?s can be created through the continuous branch.The breakdown voltage of the novel mechanical medium voltage DC circuit breaker is 61.2% higher than that of the traditional one in simulation environment.The experimental platform of intrinsic dielectric recovery characteristics is built.The inherent dielectric recovery characteristics of vacuum gap are tested with different gap and di/dt.The intrinsic dielectric recovery characteristic data show that the optimal ‘zero-voltage' time is 20-30?s which means‘zero-voltage' created by simulation is enough.Under the guidance of simulation,the prototype of the noval mechanical medium voltage DC circuit breaker and simulation circuit are put up.The interrupting performance of the traditional and novel mechanical medium voltage DC circuit breakers whose ‘zero-voltage' time is 35?s are compared.The breakdown voltage of the novel mechanical medium voltage DC circuit breaker is 34.2% higher than that of the traditional one.The reasons of the deviation between the test results and the simulation results are analyzed.It shows that the feasibility and effectiveness of novel mechanical medium voltage DC circuit breakers are preliminarily verified which provides a reference for the development of a novel medium voltage DC circuit breakers.