How do Shaded Pole Induction Relays work?

The shaded pole induction relay works on the same concept of electromagnetic induction as an induction motor works. Here is a thorough explanation of how it operates:

Operating Principle

Electromagnetic Induction

The relay is made up of two electromagnets and a pivoting metal disk. These electromagnets produce alternating magnetic fields that are out of phase with one another, resulting in eddy currents in the disc. The interaction of these currents with the magnetic fields generates torque, which causes the disc to rotate.

Shading Rings

The employment of copper shading rings around portion of the electromagnet pole faces is a crucial component of the shaded pole induction relay design. These rings generate two alternating magnetic fluxes that are separated in both time and space. The flux in the shaded area lags behind the unshaded area by a phase difference (usually 40° to 50°) caused by induced currents in the shading rings.

Torque Generation

The torque generated is the result of the interplay of the 2 fluxes & the eddy currents induced in the disc. This torque forces the disc to rotate, which moves a contact connected to it towards a fixed contact, shutting a trip circuit when a failure occurs in the system.

Restoring Mechanism

When the fault current falls below a particular level, a spring mechanism resists the movement of the disc, allowing it to return to its previous position and open the trip circuit. This ensures that the relay may reset itself once normal operating conditions are restored.

Construction Components

The shaded pole induction relay features:

A revolving aluminum disc.

Two electromagnets generate alternating magnetic fields, with copper shading rings modifying the distribution.

A spring mechanism that resets after operation.

Electromagnetic Design

The design enables efficient operation by making sure that one flux interacts with eddy currents created by another, maximizing torque output while reducing energy losses.

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