Study on Energy Stress of DC Circuit Breakers after Pole-to-pole Fault of VSC-HVDC Grid

DC circuit breaker (DCB) is the core equipment of high voltage DC (HVDC) grid based on voltage source converter (VSC). However DCB absorbs huge energy by metal oxide arrester (MOA) in it when breaking short circuit current. The overlarge energy will easily result in damage of MOA and badly limited the application of DCB. To solve this problem, this paper studies the mechanism of MOA of DCB absorbing energy after the most severe fault, the pole-to-pole fault, of VSC-HVDC grid. The theoretical calculation method of MOA energy stress of DCB is presented. A new protection strategy is provided to suppress MOA energy stress without adding any extra equipment. The actual 4-side VSC-HVDC grid is modelled and simulated based on PSCAD/EMTDC to verify the theoretical analysis results. The calculation results show that compared with the original strategy, the MOA energy stress of DCB can be reduced from 254.5MJ to 145.6MJ by using the new strategy.