[hitesh_30878]

Why the disk of induction type relay is Elliptical and in spiral shape?
Why the disk surface and surrounding area is perforated or dotted or rough?

[bhayne]

I never really thought of that. The circular disk is very common and I can see that it is probably to give equal torque on the actuator during a fault. I see this in the old distance relays that have oposing voltage and current forces (The closer a fault is to the relay the higher the current and lower the voltage; vice versa wheh the fault is far away).

Oval disks may be to generate different action on the relay (like an inverse curve or a very inverse time/current curve).

This may be the same with grooves and slots in the disks.

Unless your in a third world country, you won't see many of these being installed.

[Jasween]

The disc is in spiral shape to nullify the effect of restraining spring(used to pull the disc back to its original position when actuating force is removed) which comes in picture when the disc starts rotating.