Prahlad J. Purohit wrote:
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The minimum firing angle is 45 since the load is inductive.

How inductive, you are loading the Tx with a resistive short circuit, surely that gets transformed as a slightly more resistive shortcircuit on the primary, if the leakage inducatnce of the Tx is reasonably low. What have you measured ?
Steve

I spoke with my transformer designer regarding this on phone He tried to explain me but it went over my head. We will be discussing this issue when we meet face to face on this saturday. What I could get is "It has some thing to do with the no load primary current ie. Magnetising current". And again what I have been told is I should never fire welding transformers at less than 45 degrees angle. I will be able to give some satisfactory reason for this only after meeting our transformer expert.

Regards,
Prahlad Purohit