IEEE C37.112-2018 Annex B Coordination Worksheet (Excel)

IEEE C37.112-2018 establishes recommended practices for ground fault protection of generator stator windings, emphasizing selectivity, sensitivity, and speed—particularly for high-impedance grounded or ungrounded generator systems. Annex B provides a structured, step-by-step procedure for coordinating ground fault protection devices across multiple zones (e.g., generator neutral, bus differential, feeder overcurrent), and the associated Excel worksheet implements this procedure computationally. The worksheet integrates manufacturer-supplied TCC data (typically entered as inverse-time or definite-time curves), system parameters (fault current contributions, CT ratios, relay pickup and time-dial settings), and IEEE-mandated coordination criteria—including the 0.1-second minimum time margin for inverse-time devices and the 0.2-second margin for definite-time devices under worst-case conditions. Users input upstream and downstream device data, and the worksheet calculates actual operating times at selected fault current levels, verifies coordination margins, flags violations, and optionally generates coordination plots. It also incorporates allowances for CT saturation, relay overshoot, and timing tolerances per IEEE C37.112-2018 Section 5.3 and Annex B Table B.1, ensuring engineering rigor and compliance with industry best practices for generator protection system design and validation.