When voltage drops, current increases to maintain power output according to P=VxIxPF. This can cause overheating, overloading, and reduced efficiency in motors.

In power system, protective relay is the key link to ensure that it can accurately and reliably detect and remove faults

Relays are categorized by operation methods and response characteristics. Operation types include electromechanical, gas pressure, latching, percentage differential, solid-state, and digital relays. Response characteristics involve impedance measurement, time delay, and differential action.

High voltage circuits and transformers use two main protection relays, Main1 and Main2, with identical functions and settings but separate power sources to ensure system reliability. Protection relays from different manufacturers like MiCOM and ABB provide instantaneous and time-delayed protection for various faults.