Relay is an electronic control device. It has a control system (also known as an input loop) and a controlled system (also known as an output loop). It is usually used in automatic control circuits. It actually uses a smaller current to control a larger It is a kind of "circuit breaker" of current, so it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit.

Relay refers to a device that can produce a jump in one or more electrical output circuits when the input quantity (or excitation quantity) meets certain specified conditions. The interrelationship between the input and output of the relay in the whole changing process becomes the relay characteristic or control characteristic of the relay.
What are the types of relays?
(1) Overcurrent relay (referred to as overcurrent relay). When the current exceeds the set value, the relay will act or close the contact.
(2) Differential relay. It refers to the relay that determines the action according to the difference between the input and output of the protection device when designing or using the relay.
(3) Direction relay. A relay that operates according to the relative phase angle of current to other currents or reference voltages.