Do CTs like DC? Performance of current transformers with geomagnetically induced currents

This paper analyzes the performance of current transformers (CTs) under the presence of geomagnetically induced currents (GICs). Our intent is to qualify the impact of GICs on CT performance in the context of protection security and dependability. The paper proposes a simple method to analyze the GIC problem and applies it to explain and quantify the impact of GICs on CTs. The paper uses carefully selected simulation tools, as well as laboratory tests on a physical CT to derive and support our key findings. We summarize our conclusions as follows: GIC impact is negligible in steady states during load conditions or faults but is significant in the first few milliseconds of a fault. As such, the GIC impact is very similar to the impact of the CT remanent flux on the performance of CTs during fault conditions. This impact is significant but short-lived. The component of CT saturation caused by high remanent flux or a preexisting GIC disappears very quickly.