Impact of Geomagnetically Induced Currents on Protection Current Transformers

by  B. Kasztenny, D. Taylor, and N. Fischer,Schweitzer Engineering Laboratories, USA

This article analyzes the performance of current transformers (CTs) under the presence of geomagnetically induced currents (GICs). We conclude that GIC impact is negligible in steady states during load conditions or faults but is significant in the first few milliseconds of a fault. However, CT saturation caused by a preexisting GIC disappears very quickly. As a result, the impact to protective relays is minimal.

GICs are unipolar currents caused by earth's magnetic storms that flow in transmission lines and circulate through system grounding points, typically through wye-connected transformer windings and autotransformers. To the system, a GIC appears as a quasi-dc current superimposed onto the nominal system frequency currents. GICs remain a concern for the electric power industry, specifically with regard to the integrity of large, expensive, and difficult-to-replace assets.  More

BeijingSifang June 2016