Electrical relays are the switching circuits that sense some quantity and take an action. On the basis of working relays are divided into 9 groups:
- Electromagnetic attraction type relays contain a coil, an armature, and contacts. The coil produces armature motion and contacts are opened/closed. Electromagnetic attraction relays are of three types:
- Solenoid type
- Attracted armature type
- Balanced beam type
- Induction type relays: The working of these relays are based on the induction motors. They are only used with ac systems and can’t be employed with dc. They are also divided into three types:
- Shaded pole type
- Watthour meter type
- Cup type
- Solid state relays: These relays are made of solid-state electronic components such as isolators, transistors, and comparators. They are effective against dust.
- Numerical based/Microprocessor based relays: These are most advanced relays with multiple functions.
- Hybrid type: The input portion of such relays is electronic while switching action is mechanical. Since they lump two systems the name hybrid is given.
- Thermal overload relays: In such relay, the current passes through the bimetal of the relay and in case of overcurrent heating the strip bends.
- Insulation monitoring relay: It operates when the value of insulation resistance falls below some value.
- Liquid monitoring relays: These are used for controlling and regulating the level of the liquid.
- Gas actuating relays: These relays are actuated from the gas.
Let’s watch this video to understand it in more detail: