Bus Bars

It sounds like you have a design (or at least a rough guide) for a (similar/existing) arc furnace but want to alter the design by moving the transformer (for some reason).

Without knowing the details of your application (or even if the design and analysis has been done correctly in the first place) it is difficult to offer any practical advice other than to recheck your design calculations taking into account the increased distance.

Reducing distance and/or increasing bus bar size just for the sake of it is not a very practical way to ensure compliance (this isn't an industrial switchboard where you are only concerned about cable current and volt drop).

Perform the analysis (electrical design and site application) first before making expensive guesses that may actually make things worse (such as causing premature transformer failure).