Comparison Between 1-D and 3-D Geoelectric Field Methods to Calculate Geomagnetically Induced Currents: A Case Study

Severe Geomagnetic Disturbances (GMD) pose a threat to the reliability of the United States bulk electrical power system. The NERC reliability standard TPL-007 requires transmission planners to assess potential problems in their service territories due to Geomagnetically Induced Currents (GIC) including transformer thermal assessment. If the assessment indicates a vulnerability, the standard requires the development of a corrective action plan to resolve potential issues. GIC calculation accuracy is critical to the assessment. In this paper, the impact of various geoelectric field calculation methods on the accuracy of calculated GICis evaluated by comparing with observations for a geomagnetic storm that occurred on 07-08 September, 2017. The GIC calculation is carried out for a fairly large-scale power system model and the comparison with observation indicates that better results are achieved using magnetotelluric transfer functions that incorporate the effects of 3-D earth conductivity. The results also indicate an improvement in the comparisons when the transfer-function derived E-fields are interpolated between the original survey site locations.