Effects Of DC BIAS On Power Transformers

There has been some concern in the electric power industry that Geomagnetically Induced Currents (GIC), i.e. DC-quasi currents, have caused, and may cause in the future, significant overheating damage to large numbers of power transformers installed in some regions of the World and consequently cause large scale and long duration system blackouts, Figure 1. Based on the same principle, other sources of DC bias, depending on the corresponding parasitic DC level, may also similarly affect the transformers, for example, applications involving power electronic components, HVDC, (DC transmission or traction systems).