Research about Measurement Performance of Optic-Electric DC Current Transformer in 500kV HVDC Power System

Direct current transformer is the key device in measuring high current value of HVDC power system. Its accuracy and reliability is an important basis guaranteeing the control and protection system of HVDC grid work normal. A mal-operation event of protection relay of plusmn500 kV HVDC system of China Southern Power Grid Co., Ltd. is described. Measurement performance of optic-electric DC current transformer based on shunt measurement theory is analyzed. With the consideration of skin effect and close effect, the electro magnetic simulation about shunt is carried out. A series of frequency-dependent impedance tests about shunt in converter station are done too. The results of electro-magnetic simulation and in converter station tests are match. The research results show that the impedance of shunt will increase as the signal frequency goes high. High frequency signal will influence the measurement performance directly. Some methods of anti- interference are put forward at the end of this paper.