Effects of DC Bias on Power Transformers Tutorial for CIGRE SC A2

There has been growing concern in the electric power industry regarding the impact of Geomagnetically Induced Currents (GIC), or DC-quasi currents, which have caused, and may continue to cause, overheating of large numbers of power transformers in certain regions of the world, potentially leading to large-scale, long-duration system blackouts. Similarly, other sources of DC bias, depending on the associated parasitic DC levels, may also affect transformers. These include applications involving power electronic components, HVDC systems, and DC transmission or traction systems.
The scope of this Working Group was to address the effects of DC bias (including GIC) on power transformers and reactors and to explore methods for assessing the transformers' ability to withstand these impacts. As a…