Thanks for all the comments, dear.
Can you suggest me how to calculate the primary turns(I just need to increase the current rating in primary coil)
Secondary here is not the issue as it is already rated as per my requirement
Ferrite cores used in TV EHTs image of EHT core attached
Diameter of cyl.limb=14mm
Air Gap between limbs is =14mm
rect. limb area = 14mmX10mm
In short I wish to know how to calculate the number of turns for a particular ferrite core size/shape being two C facing each other like (2* ), accordingly I can calculate my Primary/secondary if required as I know the voltages
Pri V=220v 16khz Sec. V=25KV
Looks like a UR core to me.
At that frequency I'd imagine your limiter is your core flux density. Certainly if you want to increase the primary voltage your saturation flux density will be an issue.
Typically on the primary you are looking at applied volt-seconds. This is what increases flux in the core, and as the core reaches saturation the core loss increases non-linearly.
As a first order approximation, if you double the voltage you double the number of turns to maintain the same max flux in the primary.
If your windings are getting hot, then you can certainly increase the gauge of the wire.
using 2 cores in parallel is another way to reduce the flux density and therefore your core loss at the cost of transformer size and increased use of wire, though otherwise there isn't much of a downside.
If you need a precise magnetizing/leakage inductance then it is a different set of calculations from the ones involved in the above comments.
This isn't the best resource but it has some of the equations you need and is easier than my trying to type them in this window!!!http://www.onsemi.com/pub_link/Collateral/TND350-D.PDF
On page 16 is the basic equation for voltage, turns, and flux. That's the only page from the PDF I'd really bother with.
This also has a decent explanation of the basic core equation for flux vs turns etc.http://www.onsemi.com/pub_link/Collateral/TND350-D.PDF