Yoop,
What is the FLA of the Motor at 575V?
Use the KVA input rating of the Motor to configure the Transformer size and input FLA at 480V.
Your Voltage Increase will be 95 Volts (575 - 480 = 95), so a standard "Buck-Boost" type Transformer is not an option; the highest Secondary Voltage I know of is 48V.
An Autotransformer (pre-wound), or typical Isolated Transformer (575V to 480V Closed or Open Delta) arrangement may be needed.
Anyhow, obtain the FLA at 575 Volts to obtain the Motor's Full Load KVA, which may be converted to Transformer Capacity and Motor FLA at 480 Volts.
Example:
If the 650 HP Motor's Nameplate FLA is 640A at 575V, the KVA will be 637.44 KVA (637,440 VA)
At 480V, the FLA becomes 767.08 Amps.
The Transformer will require a Secondary with 750 KVA Capacity.
For a Buck-Boost with 95 Volt Secondary, that would result in 150 KVA capacity - as either:
1: For an Open Delta arrangement: 2x 75 KVA,
2: For a Wye arrangement: 3x 50 KVA
You might obtain (2) Single Phase 480V x 120V Transformers in 100 KVA Capacity, which you could configure in an Open Delta Network. This arrangement will result in 600V output.
Each Secondary will need to be rated at least 76.8 KVA (120V x 640 Amps = 76,800VA).
Good luck!
-- Scott (EE)
