The impact of solar storms on protective relays for saturable-core transformers

Solar storms often cause transient variations in the Earth's magnetic field. These storms are called geomagnetic disturbances (GMDs). GMDs can generate quasi-direct geomagnetically induced currents (GICs) through the neutral connections of transformers and transmission lines at the affected regions. GICs are quite detrimental to transformers because they can saturate transformer cores and generate harmonics in the windings. Power Transformers are typically protected by the commercial relays in which several protective functions are implemented. When GICs flow through a transformer, the protective relays for the transformer may be affected. Studies have shown the impact of solar storm includes reactive power loss, voltage fluctuation, and transformer heating. In this paper, numerical simulations are conducted to study the impact of solar storms on the protective relays for saturable-core transformer. Also, the commonly applied transformer protection functions in commercial relays are investigated in relation to GICs. The results indicate that the protective relays may not provide adequate protection for the transformers in the presence of solar storms.