# MW@kV conversion

First, I'm sure this question is way too easy for this forum but I didn't find a better one. I'm having an argument on the following and we'd like to settle it officially.

On a website about Diesel-Electric cruise ships, we found the following:

The entire ship—not just its propulsion system—can function with only two of the four main generators on line. Each unit generates 11.5 MW at 6.6-kV alternating current. Two electric motors provide the ship's propulsion. The motors are synchronous and run to match the frequency of the supply current. Each motor consumes 14 MW with a voltage of 2.3 kV, so the system requires transformers, as the figure shows.

How is it possible for 2 * 11.5MW (23MW) to generate enough power to feed 2 * 14MW (28MW) motors? As far as my memory of physics goes, the P=UI law, in that case, only allow me to say that

23MW @ 6.6kV ==> 1.74kA and
23MW @ 2.3kV ==> 5kA


Is it possible to say from this that

23MW @ 6.6kV = 66MW @ 2.3kV


and if so, why?

• You are right to question the write up. I would presume that if only 2 generators were on line, each motor would be limited to the available power from one generator. – Jon Custer Sep 17 at 14:18
• As noted, the clue is in the power. Transformers do not create any power (in fact they use some in losses); the total power available from the generators cannot be increased without adding more generators. In this case, the motors would not be able to run at full power. – Peter Smith Sep 17 at 15:08