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The disconnector is the key electrical equipment in DC field. In China, the ±1100 kV DC project uses the indoor DC field, where the switching impulse withstand voltage of the disconnector influences the clearance a lot. To improve the switching impulse withstand level of the ±1100 kV disconnector, first of all, the switching impulse test was carried out on the disconnector with traditional double-balanced ring structure and the 50% switching impulse discharge voltage was obtained. By analysing the discharge path, it is found that the grading ring did not effectively shield the upper part of the disconnector. Therefore, the structure of the end fittings of the disconnector was changed to the structure of the mushroom head. The electric field simulation was performed on the optimised shield，it is shown that the maximum field strength is lower than the control field strength. Then the switching impulse test was carried out on the optimised disconnector, it was found that the 50% impact discharge voltage was above 2400 kV which met the engineering requirements.

The disconnector is the key electrical equipment in DC field. In China, the ±1100 kV DC project uses the indoor DC field, where the switching impulse withstand voltage of the disconnector influences the clearance a lot. To improve the switching impulse withstand level of the ±1100 kV disconnector, first of all, the switching impulse test was carried out on the disconnector with traditional double-balanced ring structure and the 50% switching impulse discharge voltage was obtained. By analysing the discharge path, it is found that the grading ring did not effectively shield the upper part of the disconnector. Therefore, the structure of the end fittings of the disconnector was changed to the structure of the mushroom head. The electric field simulation was performed on the optimised shield，it is shown that the maximum field strength is lower than the control field strength. Then the switching impulse test was carried out on the optimised disconnector, it was found that the 50% impact discharge voltage was above 2400 kV which met the engineering requirements. [ABSTRACT FROM AUTHOR]