Effects of Geomagnetically Induced Currents on current transformer and differential protection

Geomagnetically Induced Current (GIC) has long been recognized to influence current transformer (CT). Treated as quasi-DC, the effects of GIC haven´t been discriminated from DC bias caused by High Voltage Direct Current transmission (HVDC). However, the nature of GIC as current with time-varying magnitude and random waveform makes it generate complex flux bias conditions. The differences between GIC and traditional DC bias are firstly proposed in this paper. Simulation models using low-frequency sinusoidal currents to emulate GIC are established in PSCAD/EMTDC. Furthermore, CT transient transferring characteristics in the presence of GIC are researched by theoretical analysis with simulation tests. Besides, the performances of transformer differential protection are included in respective scenarios. According to our investigations, GIC has effects on differential protection by virtue of leading CT to transient saturation or partial transient saturation. This research work will promote the development of the novel scheme of protection that immune to GIC.