Considerations for generator ground fault protection in mid size cogeneration plants

Generator ground fault protection aspects are analyzed for mid-size cogeneration plants. In these plants, the generators may be connected to a common generator bus. The overall bus connected system should be considered when applying generator high resistance grounding schemes. Calculations are reviewed for sizing generator neutral ground resistance, and evaluating third harmonics originated in the scheme. The relevant applications of third harmonic, 100% stator ground fault protection schemes are examined. Practical considerations are presented for establishing selectivity of ground fault protection schemes in the case of a common generator bus