Effects of GIC on power transformers and power systems

There is some misconception in the electric power industry today that geo - magnetically induced currents (GIC) have caused, and would cause, significant damage to the majority of large and medium power transformers installed on power grids in North America and around the world. The purpose of this paper is to present, both qualitatively and quantitatively, the true effect of GIC on power transformers, based on thorough knowledge of power transformer design and performance. The paper also provides concise explanation of the cases of transformer failure/overheating reported in the published literature to have been caused by GIC currents. The paper demonstrates that, because of the nature of the GIC currents, the great majority of power transformers would not experience much overheating or damage due to even high levels of GIC. Only some specific transformers could suffer some winding damage due to high winding circulating currents if exposed to high levels of GIC. The paper also presents the real issue with GIC; namely, the narrow pulse of the magnetizing current which results from part - cycle, semi - saturation of transformer cores when subjected to high levels of GIC currents. This one current pulse/cycle could cause relays and capacitive components in power systems, such as SVC (s), to trip, which may contribute to grid instability. Also, the current pulse is associated with 2^nd and higher order harmonics. As a result, resonance may occur, differential relays may operate, and stability of the grid may be compromised.