As a ultra high voltage direct current transmission project

and the AC filter is the key part in Pu’er converter station

which is used for filtering and reactive power compensation during operating of UHVDC project.When Pu’er converter station is operating as isolated islanding

the strategy of switching off filter is so important during bipolar blocking cases.It will cause the voltage fluctuation both in the AC system and DC system

and will also cause overvoltage on the equipment to breakdown or damage of equipment. In the case of isolated islanding model

the paper calculates the voltage with DC bipolar block by the engineering test data and specification in Pu’er converter station in order to judge that the overvoltage level whether meets the requirements of the project or not. It also gives a new strategy which applies to the ultra high voltage DC project in the filter excision aspect

which is known as time division resection strategy.