The calculation method of negative sequence and zero sequence current caused by turn-to-turn short circuit of a HV controllable reactor is analyzed.As an example， this method is used for calculation of Jindongnan-Jingmen 1 000 kV ultra-high-voltage grid in east-southern Shanxi Province and obtained useful results. According to this， a new algorithm with higher sensitivity and easy setting is proposed based on absolute value comparison for the negative and zero sequence composed direction protection criterion. Owing to the special structure of classified controllable shunt reactor and its main differential protection used to protect single-phase ground fault on HV and LV side， this paper suggests that the conventional differential protection with current transformers on HV and LV sides for common transformer is no-longer suit for the protection of controllable shunt reactor， and neither for zero-sequence current differential principle.