Instrumentation

# Explain the function of Induction Disc Relay

## What is Induction Disc Relay?

An electromagnetic relay known as an induction disc type relay operates on the electromagnetic induction principle and resembles a split-phase induction motor. The interactions of fluxes that are moved in time and space within the rotor will result in the operating force that is created.

## Induction Disc Relay Working Principle:

Similar to induction motors, induction disc relays operate on the electromagnetic induction principle. Torque is produced in these relays by the interaction of alternating flux with one of the

• Magnets and
• Eddy currents

induced in the rotor (disc) by the other alternating flux. Despite having the same frequency, there will be a phase difference between the two fluxes. These relays are therefore restricted to alternating current circuits.

This relay’s moving contact is fastened to a disc, which serves as its moving component.

## Construction of the Induction Disc Relay:

The induction disc relay is made up of two electromagnets and a rotating disc set on a shaft. In order to create two alternating magnetic fields that are out of phase and space, an aluminium disc is rotated between an electromagnet’s poles. The operating current that the relay is attached to, which serves as protection, energises the electromagnet’s coils.

## Working of the Induction Disc Relay:

The coils become energised and create a magnetic field when the system has a malfunction. Eddy currents will be induced by this magnetic field, and these eddy currents will generate their own magnetic field within the disc.

Torque is produced on the disc when the magnetic fields created by the coil’s magnetic field and the eddy currents’ magnetic field interact. Due to the rotation of the disc and movement of the moving contact toward the fixed contact, the trip circuit is closed.

The spring’s restraining force prevents the disc from moving until the fault current drops below the pickup value, which releasing the trip circuit by moving the moving contact away from the fixed contact.

## Types of Induction Disc Type Relay:

There are two types of induction disc relays:

• Watt-hour meter type induction relay and
• Shaded pole type induction relay.

## Watt-hour meter type Induction Relay:

Watt-hour Meter structure consists of two electromagnets and a disc that can freely spin between them. The lower electromagnet is formed like a U, and the upper electromagnet is shaped like an E. On the middle limb of the upper electromagnet, there are two windings (primary and secondary winding).

The ability of the relay to open or close the secondary winding circuit is its most crucial characteristic. When the secondary winding is opened, no torque is created, rendering the relay inoperable.

## Shaded pole type Induction Relay:

Copper (Cu) shading rings or coils are placed around the pole faces of each pole where there is an air gap. Two alternate fluxes are created as a result, and they are both displaced in time and space. The shaded poles’ air-gap flux is lower than that of the unshaded poles.

The flux in the portion of the iron ring that is surrounded by the ring lags in phase by 40° to 50° behind the flux in the region of the pole that is not shaded by the ring due to the magnetic field that forms from the current.

## Advantages of the Induction Disc Relay:

1. Induction disc relays are made of sturdy materials.

2. By simply opening the secondary coil, the induction disc relay’s performance can be easily controlled in abnormal circumstances.

3. The current setting and the time settings can be easily acquired by employing induction disc relays.

4. Relays of the induction disc type are accurate and dependable.

5. They can be utilised to protect against overcurrent.

## Disadvantages of the Induction Disc Relay:

1. Periodic testing and maintenance are necessary for the induction disc relay.

2. The corrosion of component parts and dust pollution have an impact on relay functioning.

3. The mechanical inertia of the component limits the induction disc relay’s operating speed.

4. Induction disc relays do not have a directional feature.

5. A high duty current transformer and potential transformer are necessary for induction disc relay.

## Application of the Induction Disc Relay:

1. Where dependability and durability are required, induction disc type relays are utilised.

2. These relay types are widely used in situations that call for slow-speed relays.

3. When a time-delay function and changeable operating time are required, induction disc type relays are used.

4. Where a high reset to pick-up ratio is required, this type of relay is used.

### Rabert T

As an electrical engineer with 5 years of experience, I focus on transformer and circuit breaker reliability in 110/33-11kV and 33/11kV substations. I am a professional electrical engineer with experience in transformer service and maintenance. I understand electrical principles and have expertise troubleshooting, repairing, and maintaining transformers, circuit breakers, and testing them. Tweet me @Rabert_infohe