A process for evaluating the degree of susceptibility of a fleet of power transformers to effects of GIC

There has been some misconception in the electric power industry that GIC has caused, and would cause, significant damaging overheating to a large majority of power transformers. A recent study by the first two authors of this paper [1] confirmed that, because of the nature of the GIC currents: (1) Only a finite number of power transformers with certain design features could experience damaging overheating (2) A larger number of transformers would be susceptible to core saturation and some overheating and (3) The rest of the transformers would not be susceptible to either core saturation or damaging overheating. This paper describes a process, where a fleet of power transformers can be properly assessed to determine the type & magnitude of its susceptibility to effects of GIC. As a result, utilities can focus their GIC mitigating efforts on those transformers that are evaluated to be susceptible to damaging effects of GIC. The proposed process has been applied to a fleet of about 1600 power transformers on the > 500 KV part of the US Power Grid. The results of this application are presented in this paper as a Case Study. It was found that 1 in 8 of this group of transformers is evaluated to be susceptible to possible damaging windings overheating; 1 transformer in 4 is found to be susceptible to core saturation but low level of overheating, and 3 transformers in 5 have low level of susceptibility to either effects of GIC.