Protective relays, overcurrent and differential protection, distance protection, bus and transformer protection, generator and motor protection, breaker failure, auto-reclosing, and synchronizing — the device-by-device logic every coordination study in Module 9 is built on top of.
This module works through the protection suite of a modern power system one device family at a time — what each one measures, what physical failure it's built to catch, and why its particular logic (time-overcurrent curves, current differential, impedance measurement) is the right tool for that specific job rather than an arbitrary design choice. Selectivity, speed, sensitivity, and security show up as the constant tension underneath every setting decision covered here, from an overcurrent relay's inverse-time curve to a generator's loss-of-field element.
By the end of this module you should be able to explain why differential protection doesn't need to coordinate in time with anything else, why transformer inrush current fools a naive differential relay and how second-harmonic restraint fixes it, and why a generator carries a wider protection suite than any other single piece of equipment in this program. Module 9 picks up immediately after this one and turns these individual devices into one selectively coordinated system.