Research On Energy Transfer Processes Of High Voltage Direct Current Vacuum Interruption

Short circuit fault breaking is a technical problem in the protection and control of High Voltage Direct Current(HVDC)transmission system.It has caused troubles in the technical fields of long-distance transmission and asynchronous networking of smart grid.In several existing technical routes of HVDC short-circuit breaking about pure solid stateand hybrid DC circuit breaker.The mechanical DC vacuum circuit breaker based on the commutation principle has the advantages of environmental friendliness,high reliability and low cost.It has become one of the best options close to the wide application of engineering.Due to the existence of natural current zero and electric energy valley bottom in conventional alternating current(AC)system,the core process of breaking is the interaction between dielectric strength recovery and system voltage recovery between current zero-cross in arc gap.However,DC breaking not only needs to consider the current transfer process,but also consider the stable consumption of energy.Circuit breaking is dominated by the energy transfer between the system and the arc,as well as the commutation circuit,and the residual energy dissipation of DC system.DC breaking scenarios also pay more attention to the energy transfer process.The purpose and background of this research is to deeply study the relevant theories of HVDC vacuum interruption and solve the technical difficulties of energy transfer in engineering application.This paper is starting from the analysis of DC vacuum interruption and its energy transfer process based on the commutation principle.It is also summarizes the spatial and temporal characteristics of the energy transfer process.The spatial characteristic includes the arc safe stroke and multi-breaking series synchronization parameters.The temporal characteristic includes arc burning time,residual energy dissipation time,commutation time and frequency.Based on the system energy transfer process,the continuous transition model of DC breaking vacuum arc is improved as a theoretical analysis tool.Combined with the characteristic parameters of DC interruption,the simulation environment is established,and the software platform is built by the joint electromagnetic transient simulation tool.According to the simulation results of energy transfer process experiment,energy control parameters taking as arc energy density,arc compound magnetic field control,zero-cross characteristic power control and residual energy consumption,the basic energy control method of breaking arc is given.The parameters description of HVDC interruption is a bridge between theoretical research and technical application.According to the theoretical definition of energy transfer process and analysis of characteristic parameters,the basic design breaking parameters of mechanical DC vacuum circuit breaker is put forward.The safe stroke and commutation time range are given.The minimum safe stroke of DC interruption is about 1 mm for 5 k A current.The commutation time is 3-5 k Hz according to the characteristic power of intermediate frequency commutation.According to the characteristics of short-time arcing and intermediate frequency commutation of DC interruption,the development and dissipation process of arc energy are analyzed.The composite magnetic field contact with coaxial transverse magnetic field(TMF)and axial magnetic field(AMF)is proposed.According to the relationship between arc image and arc energy density,the effect of magnetic field control vacuum arc is verified in the process of arc starting,arc burning and arc extinguishing.Through the above time and space characteristic parameters,the basic design of DC special vacuum switch is given.The significant difference between HVDC interruption and AC interruption is the consideration of the residual energy consumption and the corresponding experiment.Based on the residual energy evaluation and overvoltage calculation,the residual energy absorption process is analyzed and simulated.The parameter determination principle of zinc oxide(Zn O)arrester is given.Since the test circuit of conventional AC breaking cannot assess the energy absorption effect of DC interruption.This study proposes a DC synthesis test circuit and its test method with three power sources.The test platform is built to test.Transient recovery voltage(TRV)amplitude lasts for more than 10 ms.The equivalence experiment problem of the residual energy absorption capacity of the DC circuit breaker is solved.In order to test the characteristic parameters proposed in this study,the prototype design of double break HVDC vacuum interrupting module are completed.The basic parameter tests are carried out.It is analyzed that the synchronization error of the synchronous control system can be controlled within 0.2 ms.The reference basis for the synchronization error of double break in the module and the synchronization error between modules is given.The prototype test also proves the rationality of DC breaking parameter characterization based on energy transfer processes,which provides technical support for the product development of mechanical HVDC circuit breaker.