In order to filter out the harmonics generated at the AC side of the HVDC transmission system and

at the same time

compensate for the reactive power consumed by the HVDC transmission system

a certain number of AC filters must be put into operation during the operation of the HVDC transmission system

and safe and stable operation of the AC filters are crucial to the power transmission of the HVDC transmission system. In this paper

the detection of unbalanced protection

calculation of current and protection principle of the AC filters are described in detail through the the case of tripping of the unbalanced protection due to the fault of capacitor element in the engineering application of AC filters

the problem of tripping of group filters due to the fault of a single capacitor element in the setting method of current unbalance protection setting method is analyzed

the specific solution for the problem is proposed so to avoid tripping due to a single element

which is more in line with the design principles of AC filters and effectively improves operation reliability of AC filters. It strongly supports the power transmission of the HVDC transmission system

and has important reference value for the operation and maintenance of the operating station and the unbalanced protection setting of new station.