When a UHVDC project is hierarchically connected to AC grid

the performance of AC-filter breaker significantly influences the operation reliability. To study the breaking characteristics of the AC filter breaker of ±800 k V UHVDC hierarchical connection to AC grid

a circuit analysis model is established. It is concluded that when a DC line ground fault occurs and all AC filters need to be removed under the bipolar operation mode

the break recovery voltage peak value between the AC-filter breaker reaches the maximum. When all AC filters are removed during a ground fault in the AC net

the breaking current peak value is the highest. As the filter reactive power capacity increases

the breaking current of the circuit breaker increases. When cutting off a large group of filters of the same capacity

the breaking current under the small operation mode is greater than the one under the large operation mode. Under the same operation mode

the peak break recovery voltage is similar when filter groups with different capacity are cutting off. It is verified that the break recovery voltage is mainly related to the system operation mode and the AC bus voltage

but is negligibly related to the filter capacity.