Study On The Series Multi-gap Spark Gap Applying In The Multi-break DC Circuit Breaker

With the rapid development of multi-terminal Voltage Source Converter Based High Voltage Direct Current(VSC-HVDC) technology, the development of HVDC circuit breaker(CB) caused wide attention. This topic is based on development needs of long life spark gap in the multi-break vacuum HVDC CB. The paper studies on the HVDC CB and characteristics of its corresponding multiple spark gap from theoretical analysis, simulation and experimentsThe paper puts forward a new type of 320 kV multi-break vacuum HVDC CB, and mainly focus on the commutation circuit which will provide the countercurrent for CB. Using PSCAD software to build the simulation model of HVDC CB, and simulation is done under the condition of short circuit fault, circuit breaker export side lines into lightning overvoltage and operating over voltage. Considering the feasibility of HVDC CB repeatedly pass through the zero current, when the converter capacity is more than 10 μF, by changing the loop inductance value, HVDC CB can repeatedly pass through the zero current theoretically.The design parameters of multi-gap spark gap is like below: the working voltage is 320 kV, withstand voltage is more than 1000 k V, design current amplitude is more than 20 kA, single transfer charge coulomb quantity is more than 20 C.This paper uses a multi-gap spark switch connected with frequency-dependent network, which can tolerate high DC voltage, and can be breakdown reliably under low trigger voltage. Through the establishment of multiple spark gap simulation circuit and building 1, 2, 4, 10 level of spark gap experiment circuit, the parameters of frequency-dependent network is determined: the selection of equalizing resistance is 4 MΩ, voltage divider capacitance is 100 pF, number of gap series is 10, withstand voltage of single- gap is about 100 kV. And presents the complete HVDC CB circuit applying multi-gap spark gap.Finally, in view of the above key technology points, the spark gap ablation experiments of different metal electrode materials is carried out. The limit test of the ablation is done; Using three-dimensional microscope observation to observe the erosion trace, and the arc trajectory of electrode is observed as well, moreover, the electric field simulation is carried out on a flat plate type electrode. Tungsten copper electrode has passed through the 100 times discharge experiment of 50 kA, pulse width of 2.2ms, single transfer coulomb 45 C. Finally the prototype structure design of multi-gap spark gap is completed, which uses the flat tungsten copper materials for electrode, and withstand voltage of single- gap is larger than 100 kV.