What kinds of relays are commonly used?

Time relay: used in the relay protection and automatic control circuit of the secondary circuit of power system, as a time delay device to make the controlled element get the required time delay.

Intermediate relay: used in various protection and automatic control circuits to increase the number and capacity of contacts in protection and control circuits.

Over-current relay: a relay protection device for generators, transformers and transmission and distribution systems. When the equipment is overloaded or short-circuited, it can reliably act, signal or cut off the faulty part according to the predetermined time limit.

Current relay: used for overload and short circuit protection of generators, transformers and transmission lines.

Voltage relay: used in relay protection devices of generators, transformers and transmission lines, as the starting element of overvoltage protection or low voltage lockout.

Leakage relay; Used for neutral grounding loop of leakage relay with AC voltage of 660V, frequency of 50Hz and current of 1500A or below.

Relay (English name: relay) is an electrical control device. When the change of input (excitation) meets the specified requirements, the controlled quantity changes in the electrical output circuit in a predetermined step. It has the interactive relationship between the control system (also called input loop) and the controlled system (also called output loop). Usually used in automatic control circuits, it is actually an "automatic switch" that uses small current to control large current. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.

As a control element, to sum up, the relay has the following functions:

1) Expand the control range: If the control signal of multi-contact relay reaches a certain value, multiple circuits can be connected, disconnected and connected at the same time according to different forms of contact groups.

2) Amplification: such as sensitive relay and intermediate relay. With a very small amount of control, a high-power circuit can be controlled.

3) Integrated signal: For example, when a plurality of control signals are input into a multi-winding relay in a specified form, a predetermined control effect is achieved by comparing and integrating.

4) Automation, remote control and monitoring: For example, the relay on the automation device and other electrical appliances can form a program control circuit, thus realizing automatic operation.

References:

Baidu encyclopedia entry relay