Ground Fault Protection for Bus-Connected Generators in an Interconnected 13.8 kV System

The paper is based upon modifications implemented in the protection and grounding systems of a large paper mill and describes selective ground fault protection for a 13.8 kV system, with multiple bus-connected generators, synchronous bus ties and utility interconnections. The ground fault current in the system is reduced from existing 3400 A to 500 A and a hybrid-grounding system is implemented for each of the generators. As the ground fault currents are reduced to limit the fault damage, the sensitivity and selectivity of the ground fault protection becomes important. Directional ground fault relays with coordinating pickup settings are applied to achieve this objective. The new platform for directional elements (numerical relays) drives its performance from sequence-impedance measurements