Research On Breaking Parameters Of HVDC Vacuum Circuit Breaker System

High voltage direct current(HVDC)circuit breaker(CB)is the important equipment for protecting DC transmission system.The basic breaking parameters of DC-VCB include opening stroke,arcing time/commutating time,current and voltage change rate,etc.The safe stroke is the basis for determining the commutating time of DC-VCB and directly determines its dynamic breaking performance.The study of breaking parameters is the basis for the application of DC-VCB.The topological structure of the DC system and the DC breaking test platform are introduced.The simulation model is established based on PSCAD,and the equivalence between the test platform and the DC system is simulated and compared,which verifies that LC oscillation circuit is feasible as the current source of DC breaking test.Finally,the continuous transition model(CTM)is adopted to verify the influence factors of the commutation characteristics of the DC breaking test platform.This paper analyzes the breaking parameters of DC-VCB related to commutation,and it is shown that the current change rate at the zero region(di/dt)and the voltage change rate after zero(du-/dt)of the main breaker influence the breaking characteristics of DC-VCB.In the study of dynamic breaking parameters,the average opening speed of moving electrode is measured by using the measurement control system of the test platform and the operation sequence of main circuit breaker and each switch is analyzed,in order to test the influence of opening stroke on breaking ability.The main circuit breaker and each switch are tested and the initial value of time sequence is given.2kA,3kA and 4kA DC breaking tests are carried out respectively.Some breaking parameters are obtained by testing waveforms,and compared with theoretical calculation value and simulation result.The relationship between arcing time and safe stroke of HVDC-VCB under 4kA DC breaking condition is studied,and the reference values of arcing and safe stroke are obtained.The shortest arcing time and the critical safe stroke under the experimental conditions are obtained,which are 0.9ms and 2.2mm respectively.The results of this paper can be further extended to a higher current level,which is the reference basis for determining the commutation time of HVDC-VCB.The results also prove that the safe stroke and commutation time are the most important breaking parameters as well as the current change rate at the zero region(di/dt)and the voltage change rate after zero(du-/dt)of the main breaker,they are the dynamic factors that determine whether the DC short circuit current can be successfully broken or not.