Switchgear & Protection | With the help of neat sketch, explain principle of operation and working of induction type over current relay.

Principle of Operation and Working of Induction Type Overcurrent Relay: 

Figure represents the details of induction type overcurrent relay. It consists of two electromagnets, the upper magnet is of „E‟ shape & on the central limb of which are placed two windings. The upper winding acts as primary winding and lower winding acts as secondary winding.

The upper magnet produces flux ϕ1 when current flows through primary winding. The alternating flux ϕ1 of primary winding links to secondary winding ultimately induces emf in the secondary winding. The emf induced in the lower winding produces current to flow through the winding placed on the lower „U‟ magnet. This secondary current produces flux ϕ2. The two fluxes ϕ1 and ϕ2 are sufficiently displaced from each other and cause eddy currents in the disc, which will set up a torque on the disc causing rotation of the disc. The tapings are connected to plug setting bridge for giving desired current setting.