A relay is usually an electromechanical device that is actuated by an electrical current. The current flowing in one circuit causes the opening or closing of another circuit. Relays are like remote control switches and are used in many applications because of their relative simplicity, long life, and proven high reliability.
The electromechanical protective relay converts the voltages and currents to magnetic and electric forces and torques that press against spring tensions in the relay.
The tension of the spring and taps on the electromagnetic coils in the relay are the main processes by which a user sets in a relay.
Types of relay