Transformer sizing?

Hi, I am just beginning my journey into CNC and would like some info
or links regarding transformers sizing for stepper motors (constant
current supply).

I am confused regarding the real operating VA requirement for
transformers, Average current draw and peak, etc.

I have seen the figure of 67% mentioned. Is this for one winding or
for both.

Kindly point me in the right direction.

Many thanks

JV