A method to assess GIC impact on zero sequence overcurrent protection of transmission lines

Geomagnetically Induced Currents (GIC) induced by a geomagnetic disturbance on the Earth surface, may saturate transformer cores. A saturated transformer draws more reactive power from the grid and injects harmonics into the grid. Subsequently, this can compromise the operation and reliability of the protection systems. It is important to identify the vulnerability of the protection schemes during GIC and to take appropriate remedial measures. This paper presents a method to assess the impact of GIC on the protection. With this method, the assessment of a complicated GIC scenario is converted to a simple fault calculation. In this paper, the application of the proposed method on the zero-sequence overcurrent protection of the transmission line in Hydro One transmission system is discussed. It is shown that the zero-sequence current under GIC conditions can be calculated by applying the line-to-ground and double-line-to-ground fault at the two ends of the line. As a part of an asset management strategy, the proposed approach can result in a significant saving in the equipment investment by identifying the problematic protection schemes having the GIC issues.