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Bookman · 26th Mar 2020, 10:07 am

What you have is relatively simple to explain and indeed Herald 1360 has more or less provided an accurate response, I refer.
Most three phase transformers are connected Delta/Star in which the primary Voltage is the phase Voltage and in this case will be 415 Volts. That is, each transformer winding will provide its nominal output if 415Volts is applied to the primary.
If we apply a 1ph 240V supply to the primary the output Volts will be 240/415 x 24V = 13.88V approx at no load.
We must then assess the VA requirements that you are seeking namely 150V x 25A which is 3.75kVA which is substantially in excess of the output of the transformer you have stripped down. In this I am referring to its current nominal output of 24V/40A DC output = 960VA.

The latter would suggest you put the item aside for a rainy day and seek another solution.

26th Mar 2020, 10:07 am	#7
Bookman Hexode Join Date: Aug 2017 Location: Taunton, Somerset, UK. Posts: 318	Re: Three phase transformer What you have is relatively simple to explain and indeed Herald 1360 has more or less provided an accurate response, I refer. Most three phase transformers are connected Delta/Star in which the primary Voltage is the phase Voltage and in this case will be 415 Volts. That is, each transformer winding will provide its nominal output if 415Volts is applied to the primary. If we apply a 1ph 240V supply to the primary the output Volts will be 240/415 x 24V = 13.88V approx at no load. We must then assess the VA requirements that you are seeking namely 150V x 25A which is 3.75kVA which is substantially in excess of the output of the transformer you have stripped down. In this I am referring to its current nominal output of 24V/40A DC output = 960VA. The latter would suggest you put the item aside for a rainy day and seek another solution.