Relay Classifications

•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

•Electro Magnetic relay,

•Static relay and

•Mechanical relay.

•Actually 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 electromagnetic relay these closing and opening of relay contacts are done by electromagnetic action of a solenoid.

•In mechanical relay, these closing and opening of relay contacts are done by mechanical displacement of different gear level system.

•In 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.

•Based on of logic the protection relay can be categorized as

 1. Differential
2. Unbalance
3. Neutral Displacement
4. Directional
5. Restricted Earth Fault
6. Over Fluxing
7. Distance Schemes
8. Bus bar Protection

 9. Reverse Power Relays 

10.Loss of excitation

 11.Negative Phase Sequence Relays etc. 

•Based on actuating parameter, the protection relay can be categorized as

  1. Current Relays
2. Voltage Relays
3. Frequency Relays
4. Power Relays etc.

•Based on application, the protection relay can be categorized as

1.Primary Relay

2. Backup Relay

•Primary relay or primary protection relay is the first line of power system protection whereas

•Backup relay is operated only when primary relay fails to be operated during fault. Hence backup relay is slower in action than primary relay.