is it advisable to size the capacitor bank as 30% of the transformer KVA rating? I assume KVAR=30% Transformer KVA

It is because of the stored calories and carbohydartes which is not soluble during digestion, as called resins in our stomach

From your power angle formula you can size your capacitor depends upon how much power factor you are going to correct..

The total connected load both inductive and resistive in a plant is around 130 HP What size of capacitor bank is to be installed to have a power factor around 0.90 ?

The total connected load both inductive and resistive in a plant is around 130 HP What size of Capacitor bank is to be installed to have a power factor around 0.90

Find a company offering "Dynamic" correction equipment. Dynamic equipment monitors your demand and follows it, so to speak, will save you more than a static capacitor bank.
The equipment distributors will do calculations for you, although I would prefer a good electrical engineer who is working for you without the vested interest of selling equipment.

First measure the present pf,then from charts you can get Var required to correct to 0.9. If the load varies during duty/working hours connect a power analyser or datalogger to record I,V Hz, pf,harmonice,MD,THD etc and give it to a professional PFCC installer to give you a report and quotation for installation of a suitably rated PFC bank including harmonic filters,if required.