Induction Disc Relay-Construction,Working

Induction Cup Relay Construction 

Induction Cup Relay is also a type of  induction disc relays.The basic principle on which induction cup relay works is same as that of induction motor. In construction also it is identical to induction motor.
Note: If you know the working of induction motor,then this article will be very easy to understand read working of induction motor here
Structure of induction cup relay is Shown in figure.

Induction Disc Relay-Construction,Working
Induction cup relay consist of following parts, 
(a) Stationary iron core (stator)
(b) Hollow cylindrical cup (rotor)
(c) Electromagnet and
(d) Coil.

1.Stationary iron core acts as stator which consists of two, four, or more poles. Now-a-days it is constructed for 4 or more poles.

2.Hollow cylindrical cup acts as rotor similar to a disc in other two relays. It is free to rotate in air gap between electromagnet and stationary iron core.

3.Electromagnet creates magnetic field.

4.Induction cup relay consist of two pairs of coil, when these coils are energized, flux is produced in the coils. These fluxes will have same frequency but will have phase delay (0 to
  ). These coils will then energize iron core thus producing a rotating flux in the air gap.

Induction Disc Relay Working

Due to these fluxes, eddy currents are made to circulate in rotor. Thus it will give rise to a force which acts on rotor. So, the hollow cup, rotates. in the direction of magnetic field between magnets and stationary iron core.

There is a control spring and back stop attached to spindle of cup to avoid rotation of rotor continuously.

Advantages of Induction Cup Relays

1. In induction cup relays the inertia of cup is much lesser than that of disc in induction disc relays.

2. Induction cup structures have very high torque to weight ratio and are therefore very sensitive .

3. They are very fast in operation due to light rotor (the operating time is less than 0.10 seconds) and are therefore suitable for high speed operation.

4. The leakage in magnetic circuit is minimum in induction cup relays due to more efficient magnetic systems. This also reduces the resistance to the induced current path in rotor.

5. Because of efficient magnetic system and light weighted rotor Volt-Ampere (VA) burden is greatly reduced in induction cup relays. The torque per VA is about three times that of induction disc relays.

6. Induction cup relays can be made to have linear characteristics by proper design. They can be made to operate accurately over a wide range with high ratio of reset to pick—up value.

7. They produce a steady non—vibrating torques.

8. The parasitic torque due to current or voltage alone is small in induction cup relay.

9. They are inherently less sensitive to D.C transients.

10. Induction cup relays are best suited for protection where the normal and abnormal conditions differ marginally.