GIC mitigation: a neutral blocking/bypass device to prevent the flow of GIC in power systems

The design of a neutral blocking/bypass device which can be installed in power transformer neutral-ground connections to block the flow of geomagnetically induced currents (GICs) is described. The device consists of standard distribution capacitors which provide the GIC blocking function. The capacitors are rapidly bypassed by a combination of sparkgap and circuit breaker to solidly ground the neutral during power system disturbances. The sparkgap provides the fast operating response speed, while the circuit breaker provides a secure metallic bypass of the capacitor. Simulation indicates that the bypass device operation will occur rapidly (on the order of 1 ms or less) and will both prevent ferroresonant overvoltages and preserve proper relay and protective device operation