power factror is very less(0.3)

put capacitor bank

what factor sould i consider for calculating the value of capacitor bank

Limits within which the power factor - in fact the KVAr is varying (after all you compensate the KVAr) then you should put a APFC in line

Just the way you do not go for a high lagging pf, you shouldn't land up in a high leading pf either.

Looks to be the only choice is APFC (or may be convert them into DC Motors or some other type where the load does not spoil the powerfactor so much.

Connect capacitor bank to your main incomer bus. Use two Capacitor banks if you have two bus sections.

Induction motors running through DOL Starters - driving what?

The pf of 0.3 means (if measured correctly) these are on almost no load.

If it is so then why are they running at all?

Why don't you put proper sized motor ?

Putting capacitor etc is all OK but why the motors are so excessively over-rated?

Put in a Somar Integra motor regulator for each motor.

One of its functions is to provide soft-start. It also has very many other control and protection functions.

As concerns power factor, it greatly corrects power factor for motors. Since your power factor is so low, this mean sthat your motors are operating at very low load or that the motors are too big for what you're doing with them. Despite that, Somar Integra motor regulators will continually raise the power factor for each motor up to 90%+.

Here is Somar's website. Just ask Somar who distributes and provides services for Integra regulator in your area.

http://www.somar.co.uk/energy-saving-technology/Integra-motor-control.php

Good luck! DZ

Don't start the motor...

It sounds as though the motors are oversized for the job.

Review the provision of motors and their matching to the connected mechanical loads.

Switch off unused motors.