The article provides an overview of protective relaying principles and their applications for high-voltage power system components. It covers the protection methods for generators, transformers, buses, and transmission lines using various relay types to detect and isolate. Relay protection is the discipline of designing schemes that detect faults, coordinate relays, and isolate equipment without outages. It functions as a watchdog by constantly surveying multiple system components including voltage, current, frequency, and phase angle. CT's transform line current down to a signal level that is.