In case of DC fault of the DC transmission system with a high proportion of new energy

the large reactive power disturbance and weak effective support of the new energy lead to the rise of voltage level of the system and also mutual influence and restriction of the new energy consumption level and DC transmission power in the near area. For solving above problems

a kind of new energy transient over-voltage suppression method based on controllable transformer is proposed. The DC power supply is used to control the saturation degree of the transformer core

making it have the reactive power compensation function similar to the magnetic control reactor so as to suppress the over-voltage of the new energy generator terminal. Firstly

the feasibility and controllability of transformer as inductive reactive power source are demonstrated

and the mathematical model of transformer controllable reactance based on excitation current regulation is set up. The excitation control system of the transformer is designed so that the transformer can automatically control the saturation degree of the core in accordance with the voltage level of the system

change its reactive power and thus suppress the over-voltage. Finally

the effectiveness of the method is verified by the example of near DC area of Qinghai Xinjiang power grid.