Power System Selectivity: The Basics of Protective Coordination

The intent of this article is to provide a brief primer about the essence of coordinating the basic protective components of the electrical power system, including circuit breakers, fuses and protective relays, and to enable the reader to review a plot of time-current curves and evaluate several key concerns:

• How well do the devices work with each other?

• Will a minimal amount of the power system be lost by a fault?

• How well are the power system components protected?

• Could the chosen ratings and settings cause nuisance trips?