Wiring 37.5 KW generator
Wiring 37.5 KW generator
(OP)
Greetings,
I posted some questions re. this generator a month ago and got some very useful information. Thanks for all of your help.
I have had some time now to inspect the generator. In order to facilitate things I have posted pics, comments and questions on a web page.
At the end of the web page I have several comments. Would you comment on these? Please see the following page first:
http://jhdpetro.com/detroitdiesel.html
Questions:
1) So would I be correct in assuming that this generator is actually wired for three phase wye and that if the owner was getting single phase out of it that he was only using one of these three phases?
2) If I want to optimize it for a single phase, should I wire it as below?
3) If the answer to #2 is yes, this will get me 2/3 of the power of the generator or double of what the previous owner was getting, right?
4) If I want to use it for home use, would I be correct in assuming I must use the transformer in order to get a center tap to provide a neutral for 120V loads?
This is the prior thread re this generator - general questions re. applying a 3-phase generator to a single phase application:
http://www .eng-tips. com/viewth read.cfm?q id=252227& amp;page=1
Regards,
DJ
I posted some questions re. this generator a month ago and got some very useful information. Thanks for all of your help.
I have had some time now to inspect the generator. In order to facilitate things I have posted pics, comments and questions on a web page.
At the end of the web page I have several comments. Would you comment on these? Please see the following page first:
http://jhdpetro.com/detroitdiesel.html
Questions:
1) So would I be correct in assuming that this generator is actually wired for three phase wye and that if the owner was getting single phase out of it that he was only using one of these three phases?
2) If I want to optimize it for a single phase, should I wire it as below?
3) If the answer to #2 is yes, this will get me 2/3 of the power of the generator or double of what the previous owner was getting, right?
4) If I want to use it for home use, would I be correct in assuming I must use the transformer in order to get a center tap to provide a neutral for 120V loads?
This is the prior thread re this generator - general questions re. applying a 3-phase generator to a single phase application:
http://www
Regards,
DJ






RE: Wiring 37.5 KW generator
2) Use the lower diagram in the pictures for single phase. That would be the diagram labeled MONOPHASE SINGLE PHASE.
3) Yes and no, maybe.
You will get 2/3 of the three phase KVA on a proper single phase connection.
The power factor may have been 0.8, if so the power factor will be i.0 on single phase. Your available kW on single phase will be 0.83 of the three phase rating if your set is rated at 0.8 PF. If your rated power factor is 1.0 or 100% then the three phase output will be 2/3 of the three phase output.
Sell the transformer, you don't need it. The 4,5,10,11 connection labeled M on the MONO PHASE diagram is your neutral connection. You should get 120 Volts and 240 Volts with a zero phase angle. (I don't have much patience with reversed connections on single phase being called a "180 degree phase shift")
It should work for you.
Good luck.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Wiring 37.5 KW generator
1) I do recall that the label stamped on the generator stated the PF was 0.8 - so that would be a good thing(?) as this allows me more power?
2) Is this config in the diagram you refer to the 'zigzag' configuration?
3) Referring to the labels on the diagram, just to confirm things - I would find 240V measured from 'L3' to 'L2' with 'M' being a middle center tap reading 120V to either L2 or L3 and all of these being in the same phase?
Wow, too bad the poor guy who had this setup before me didn't have you guys as a reference! He paid a bunch of money for that transformer - more than I paid for the entire package - generator, xfrmr, control system, fuel tank.
4) Well one more question - Do 3-phase generators have 6 sets of windings for versatility? So they can either be paralleled or stacked for different voltages? (Or I guess you could have two different, but electrically isolated virtual generators at the lower voltage.)
RE: Wiring 37.5 KW generator
Some generators are designed for reconnection and 12 leads brought out to allow reconnection for various voltages from 120 to 480. The regulator and exciter are also designed for reconnection in this case and the generator tags usually indicate the available connections and any steps necessary for reconfiguring the exciter and regulator.
Other generators are not wound for reconnection, they have no leads except for the ones necessary for the single voltage/phase arrangement on the tag. Old Onan's are noted for this, 95% of the time, if it's not listed on the generator tag, it's not available from an Onan. Onan made plenty of reconnectable sets, which are labled with all the voltages and amperages, but don't expect to find one when you look in the connection box unless it's designated on the tag.
Old Kohlers tend to have the 12 leads, but not have the exciter and regulator designed for reconnection without swapping out parts. In this case, an aftermarket system is frequently the best option. You get modern components and design instead of something with 30-40 year old components which are frequently NLA from the manufacturer or very expensive if available.
RE: Wiring 37.5 KW generator
See the first photo. What do you make of the small, 3 phase current monitoring transformer that the generator leads run through? There is a connection strip with small white wires that used to run back to the original control system. Those leads are no longer used.
However, there is one pair of wires (the thicker and yellowed ones) that runs back into the generator unit. I wonder if this provides any direct feedback to the generator in terms of regulation of any sort. Could this be a problem with rewiring to zig zag configuration?
I'll include some photos of the rest of the system at some point.
Thanks again.
DJ
RE: Wiring 37.5 KW generator
A typical generator may be rated for 50KVA, 40 kW, PF 0.8 (80%)
The KVA is the product of the current that the generator windings may safely carry without overheating and the rated voltage. I had a customer who needed a 40 kW set at 208 Volts.
The supplier stuffed him with a 40 kW set at 240 Volts.
The set was 208/240 or only 87% of what we needed.
Back on topic, the 40 kW, 50 KVA will typically have enough engine power to produce 40 kW.
If this set was reconnected for single phase, the KVA rating would drop to 33 KVA. The engine has enough power for 40 kW so the set may be rated at 100% PF and still have power to spare. Make that power to burn if you overload it.
Now the Automatic Voltage Regulator will likely be set for 208 Volts. When you start it, it will produce 104/208 Volts. Tweak the AVR up to 240 Volts and you're good to go.
(The windings originally developed 120 Volts but phase to phase, where the majority of AVRs are connected, there would be 208 Volts and that's what the AVR would have been set for.
2) Yes, that is the Zig-Zag connection.
3)Yes 240 Volts from L3 to L2 (after you tweak the AVR.
4)Yes, they may be series, paralleled, connected in star, delta, four wire delta, double delta, Zig-Zag or Bar-Diamond or Collins. (Double delta is now the preferred connection for single phase and the Collins connection is used to connect a 10 lead set for single phase.
Thank you for your comments ccjersey. AS per ccjersey's comments. You may have to replace the AVR. Check back here first.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Wiring 37.5 KW generator
DJ