Rewiring a Geneator???

[charlie b]

I did a "shipcheck" (walk-through, inspect, take notes, take pictures, etc.) last Friday on a small, 40+ year old vessel that the Navy once owned, and that is now used for transporting commercial goods up small rivers. It is in drydock, undergoing some major repairs. My job was to get the information necessary to create an accurate one-line diagram.

There were two new diesel generators being installed. The nameplates described them as 120/240 volt single phase. But the vessel has several motors larger than 15 horsepower, so I know three phase is needed. When I mentioned this to the shipyard's "port engineer," he said they already knew that, and had already fixed the problem. He said that there were twelve wires coming from the generator, that the wires had been configured to give a three-phase output, and that they just didn't bother to change the nameplates.

It sounds like wishful thinking to me. Is this really possible? Can you reconfigure a generator in this fashion?

 

[Pierre C Belarge]

I saw David Blaine on TV last night. He is a magican. I believe in his TV downtime, he magically rewires single phase generators into three phase ones. Thats what it would take.

I believe he levitated the generators into position too :wink:

 

[don_resqcapt19]

I worked on one a long time ago that was 1 or 3 phase. I think the 3 phase could be wired either delta or wye, but the single phase used something that they called a "Z" connection. It ran the single phase current through two windings for one leg and a single winding for the other leg. One point of the "Z" was the neutral.
Don

 

[qcroanoke]

Yes, it is possible to re-wire a genset from single phase to three phase.
But it must be a 12 lead genset.
Usually you will find a wiring diagram on the inside of the generator
where the connections are made showing what leads to connect for the voltage and Phases you want.
I'm pretty sure if you go from single phase to three phase there is a significant difference in the amperage output. But don't quote me on that. :wink:

 

[tshea]

I saw David Blaine on TV last night. He is a magican. I believe in his TV downtime, he magically rewires single phase generators into three phase ones. Thats what it would take.

I believe he levitated the generators into position too :wink:

I saw that too. He was near a drydocked ship :roll:

We have rented generators that had a switch on the inside that allowed you to switch between 120/240 1 ph 3 wire , 240 v 3 phase 3 wire and something else (can't remember).

I do remember you could not get 3 ph 4 wire from that generator.

 

[don_resqcapt19]

Look at the last two on this sheet.
Don

 

[charlie b]

Thanks for the replies. The Port Engineer did say that it was a 12-lead machine. So I'll quit worrying about it, and draw up the one-line with a couple 3-phase 480V generators.

 

[oliver100]

The main distribution panel should give you a clear indication for the on board electrical distribution system. Some name plates on the large motors should give you the voltage. It will be interesting to know the frequency. If the ship is converted under an American Flag, and originally built under a foreign flag the frequency could be 50 HZ. Again the name plates of the motors should indicate that 3600 vs 3000 RPM 1800 vs 1500 RPM synchronous speed etc.

Some of the old systems (radars, gyroscopes etc) require 400 HZ (motor-generator).

 

[tkb]

Would the KVA rating be the same on single phase and delta or wye three phase?

 

[charlie b]

In general, a machine's KVA rating is based on its ability to reject heat to the surrounding area. One might guess that that would not change just because you connected the 12 wires in some other way. However, the ability of a machine to reject heat might depend on the rate at which it is internally generating heat. So it is possible that the KVA rating would change, if you rewired this generator for 3-phase.

 

[charlie b]

Some name plates on the large motors should give you the voltage.

Here's the generator's nameplate:

 

[don_resqcapt19]

Charlie,
It would be at least 1/3 less when used as a single phase machine then when used as a 3 phase machine. One winding is not providing any useful power in the single phase configuration.
Don

 

[oliver100]

Here's the generator's nameplate:

If the generator has 3 phase windings (as shown in Don's link) most likely the "port engineer" has done his part. Of course checking the voltage on idle is prudent.

It would be at least 1/3 less when used as a single phase machine then when used as a 3 phase machine. One winding is not providing any useful power in the single phase configuration.

Don
for the last three configurations (double delta, parallel low zigzag etc) your link indicates 50% less KW/KVA in a single phase configuration.

 

[don_resqcapt19]

The manufacture's drawings show it as a 3 phase alternator, but they do not show the connections for a 3 phase output.
Don