What is Relay :
A relay is an electro-mechanical switch which is used to open or close a circuit . It’s operated by a relatively small electric current, which is capable of sensing abnormal conditions in electrical circuits. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal.
How many types of Relay in protection system:-
1. Electromagnetic Relays :
These types relays are those relays which are operated by electromagnetic action. Its are constructed with electrical, mechanical and magnetic components, and have operating coil and mechanical contacts. It will be used in Magnitude measurement, Comparison, Ratio measurement , etc. It will take much longer time to replace all electromagnetic relays by micro processor based static relays. This will be operated in A.C supply or D.C supply.
2. Solid State Relays :
A solid-state relay (SSR) uses solid state components to perform the switching operation without moving any parts. The main advantages of this relay are its long life span and faster switching operation compared to the other relays. This types relay have fast switching speeds compared with electro-mechanical relays, and have no physical contacts to wear out.
Used of Solid state relay:-
- Thyristor, TRIAC or other solid-state switching device.
- Power semiconductor devices such as Thyristors and Transistors, to switch currents up to around a hundred amperes (100Amp).
- For faster switching operation.
3. Hybrid Relay :
4. Thermal Relay :
5. Reed Relay :
6. Safety relay :
Used of Relay in Protection System:-
- Relays are used in the traffic signal controllers, temperature controllers.
- Used in variety of applications like Eectric power systems, Home appliances, Automobiles, Digital computers, Industrial equipments, etc.
- The main operation of this device is to make or break contact with the help of a signal without any human involvement in order to switch it ON or OFF.
Inventor of Relays:-
Carl Friedrich Gauss and Wilhelm Weber developed an electromagnetic relay in 1833.