What are the classification and role of relay

(1) Current relay: Acts to reflect the increase of current, as a starting component and measuring component for current protection.
(2) Voltage relay: It acts to reflect the change (over or under) of the voltage.
(3) Time relay: used as a time component to establish the necessary action delay.
(4) Intermediate relay: its function is to increase the number of contacts in order to control different circuits; increase the contact capacity to open or close the circuit of larger current; provide the necessary delay to meet the protection and automatic device Requirements.
(5) Signal relay: In the protection and automatic device as an action indicator. In the action, on the one hand, there is a drop indication or a light indication, on the other hand, the mechanical self-holding electric shock is closed, and the lighting and sound circuits are turned on. Then the duty staff will go back manually.