Mission Brief

The Coordination Study

FortisBC asks you to issue the protection coordination study for a 4.16 kV distribution bus. A 25/4.16 kV transformer feeds a bus with a main incomer relay (R1); a feeder relay (R2) protects a cable run to a fused motor lateral. The settings on file don't fully coordinate — a feeder fault risks tripping the main, the fuse and relay overlap, and the motor nuisance-trips on start. Build a scheme that is selective AND protects every piece of equipment.

• Read a Time-Current Coordination (TCC) chart with damage curves
• Coordinate R2 below R1 with the minimum CTI (IEEE C37.112)
• Keep both relays below the transformer and cable damage curves
• Back up the lateral fuse and ride through motor starting
• Use the live model — change a parameter, see the whole study update