Protective-Device Coordination Studies

Coordination studies are performed to ensure that transformers, capacitor banks, electric motors, and cables are protected against damage from short-circuit currents. These studies are used to select appropriately rated protective devices and their settings. The objective is to minimize the impact of short-circuits in the electrical system by isolating faults as quickly as possible, while maintaining power to the rest of the system.

Coordination studies take into consideration the pre-load and ambient-temperature adjustments on fuse minimum-melting curves, transformer magnetizing-inrush current, full-load current, hot-load and cold-load pick-up, coordination time intervals for series-connected devices, and the type of reclosers and their reclosing sequences.

Locked-rotor motor starting curves, thermal and mechanical damage curves for cables and transformers, and generator performance curves are plotted along with protective-device time-current characteristic curves. S&C uses the latest software tools—CYMTCC for Windows®, ASPEN DistriView, and SKM CAPTOR—to generate the time-current characteristic curves for all protective devices on each feeder.

Coordination studies for industrial and commercial facilities are performed in accordance with accepted industry practices and procedures, consistent with ANSI/ IEEE Standard 242-2001, “IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems”. Coordination studies for electric utilities are based on their specific fusing and reclosing practices.