Types of Relays
Types of protection relays are mainly based on their characteristic, logic, on actuating parameter and operation mechanism.
Based on operation mechanism protection relay can be categorized as electromagnetic relay, static relay, and mechanical relay. Actually, the relay is nothing but a combination of one or more open or closed contacts. These all or some specific contacts the relay change their state when actuating parameters are applied to the relay. That means open contacts become closed and closed contacts become open. In the electromagnetic relay, these closing and opening of relay contacts are done by the electromagnetic action of a solenoid.
In the mechanical relay, these closing and opening of relay contacts are done by mechanical displacement of the different gear level system.
In the static relay, it is mainly done by semiconductor switches like thyristor. In digital relay on and off state can be referred as 1 and 0 state.