problem is that switch or transformer get heated when we apply voltage above 90(at that time current is 0.95A).
At the same ratio (carried to your intended 230V) it suggests your primary will carry 2.4 A at 230 V. The primary winding should be 17 AWG, to carry this amperage safely.
The power will be 559 W, roughly. Some of it is resistive, creating heat. Some of it is reactive. Expect 10 to 15 percent losses. The heat could be equivalent to a 60W incandescent bulb.
You can expect the primary to carry peaks of 4 or 5 A. Did you construct the transformer with sufficient metal mass, to be certain it will not saturate at this current?
Do you plan to draw 559 W from the secondary (at 5 or 6V)? That will be 93 amperes. I'm not sure it will be feasible. The resistance in the secondary loop cannot be greater than .064 ohms.
Or does your secondary need less power? Then it might help if you design your primary so it does not draw so many amperes, either at 90V or 230V.
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Links to charts of wire gauges showing safe amp-carrying capacity:
http://amasci.com/tesla/wire1.html
http://www.technifest.com/wire_gauge.htm
http://www.powerstream.com/Wire_Size.htm
Here's a link to another wire gauge table. Its ampacity values are much different than the other tables.
http://www3.telus.net/chemelec/Projects/Wire/Wire-1.png
Possible reason for the disparity: One source may base ampacity on a higher temperature which makes the wire get too hot to hold, while the other source may use a lower temperature where copper's electrical characteristics start to change even though it is only warm.
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http://www.helukabel.de/pdf/english/technik/X_081_Current_ratings_for_UL-CSA_cables.pdf