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Transformer sizing crieteria

Transformer sizing crieteria

Transformer sizing crieteria

Can someone guide in calculating transformer size for 1 mega watt DC motor with following specs.

Power: 1 Mega watts
Rated voltage: 700
Base RPM: 30
Field current: 240 Amps

Rated current: 1700 Amps

My application is plate rolling mill where current goes up to 3600 ampere, that is where we have set our High speed circuit breaker. Earlier this application was running with MG set, it is a reversible rolling mill.


RE: Transformer sizing crieteria

Stick with the MG set.
You can't run a DC motor directly from a transformer.
You will need an electronic drive to feed the motor if you ditch the MG set.
The drive will need to be oversized to handle overloads of 200%+.
The drive manufacturer may want a special transformer or may supply the transformer as part of the drive.
The drive manufacturer may want a 6 phase or 12 phase output to reduce ripple and harmonics.
The drive manufacturer may want a transformer with a specific impedance.
For a new installation, consult the drive manufacturer for transformer specs.
Consider also an AC VFD drive. Again, consult with drive manufacturers.
For an existing installation, repair the MG set.

"Why not the best?"
Jimmy Carter

RE: Transformer sizing crieteria

sorry waross I could not provide the full information, actually it is an up gradation project where we are replacing MG set with a 4 quadrant dc drive with 5000 amperes armature current. The drive supplier is also responsible to provide rectifier transformer with 2 secondary winding of one star/delta each. But the rated power for above transformer is 3 MVA which seems high for 1 mega watt dc motor, so i wanted to know how the sizing should be calculated, considering safety margins etc.

RE: Transformer sizing crieteria

3MVA doesn't seem particularly oversized considering what you have posted.

RE: Transformer sizing crieteria

5000 Amps x 700 Volts = 3,500,000 Watts = 3.5 MW.
(5000 Amps + 240 Amps Field) x 700 Volts = 3.67 MW
3.67 MW x 1.25 = 4.6 mW
4.6 MW / unknown distortion PF = 5 MW
I agree with Lionel.

"Why not the best?"
Jimmy Carter

RE: Transformer sizing crieteria

Thank you very much and sorry for the late reply

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