# 277-480 3 Phase Generator to single phase

• posted

Help please we are being given a a 50kW generator that puts out 3 phase

277-480 volt 3 phase, just have to pick it up. How do we use this with our sinle phase building? This is a serious question, if it cost too much then we will pass on the generator, so please help.

Sandy

• posted

| Help please we are being given a a 50kW generator that puts out 3 phase | 277-480 volt 3 phase, just have to pick it up. How do we use this with our | sinle phase building? This is a serious question, if it cost too much then | we will pass on the generator, so please help.

Whether or not this is practical depends on the design of the alternator. Many generators are of the "12 lead" variety, meaning they have 6 windings in the alternator. Others are of the "6 lead" variety and have 3 windings in the alternator. Many have adjustable voltage controls.

The "12 lead" type would have 2 windings in each of the 3 phases that can be wired in series or in parallel. In series, you can get from 220 to 277 volts. In parallel, you can get from 110 to 139 volts.

If this generator can be reconfigured by rewiring the terminals in the main control box, it would be possible to arrange the connection to the

3 windings into what is known as a "double delta" configuration. This is done by taking 1 each of the 3 phases and wiring them into a delta arrangement (with the proper phasing to avoid a "short"). The other winding of each of the three phases would also be wired the same way. Now these two deltas are wired so that the 2 windings of ONE of the 3 phases is wired end to end, just like in series. You end up with a configuration that graphically looks like (use Courier fixed font if this does not display well):
• * / \ / \ / \ / \
*-----*-----*

Arranged this way, one phase (the one in series) will supply about half the capacity. The other two phases will team up to supply the other half of the capacity. Those other two phases will be running at a low power factor of 0.5, so they will have an equally high current, but only supplying a low amount of real power. The total capacity of a 50 kW generator will then only 33.33 kW (2/3 of the three phase capacity).

The voltage regulator would normally be set higher (138.5 volts per winding) for the 277/480 setup. It will have to be lowered to 120 volts for the 120/240 double-delta setup. That may lower the total capacity depending on the kVA and/or current rating.

An experience generator technician or engineer would know if this one can be reconfigured or not, and probably know how to do it if it can.

If you can tell us the exact make and model (should be in the nameplate) someone may be able to be more specific. Also tell us how much power you need out of the generator short-term and long-term.

Other options exist, but are more expensive. They include transformers and dividing your building wiring three ways. Since you are being given the generator, it sounds like any big expenses are probably not an option for you.

• posted

Where in the world are you? I have never seen a service in North America that has single phase 480.

• posted

|> Sandy | | Where in the world are you? I have never seen a service in North America | that has single phase 480.

He didn't say the service to the building was 480 volts. I would presume he has 2 dilemmas ... the phases ... and the voltage. So that is why I responded with my post about reconfiguring it (if that can be done with the model he's getting) to double delta at 120/240 volt. I am assuming his single phase utilization voltage is 120/240.

You can get single phase 480 volt service in many places. Not sure why anyone would want it unless their service drop was particularly long and they were willing to spring for a transformer.

• posted

Thank you for your reply, and we infact have 120 single phase this gift may cost more then we save.

• posted

| Thank you for your reply, and we infact have 120 single phase this gift may | cost more then we save.

That is very likely. If it can be reconfigured for double-delta at 120/240 volts, and if you don't need more than 2/3 of its capacity, you could still use it. Otherwise, you should be looking for a single phase unit. What power capacity and power factor do you need?

• posted

I don't know yet. My other half (who is out of town) will have to take care of that end. I am just trying to get as much info I can before he gets back and I tell him about the offer. When I find out I'll let you know.

Sandy

• posted

or you could just buy a 480-208 3 phase transformer.

• posted

| or you could just buy a 480-208 3 phase transformer.

He'd still only be able to use 2 of the 3 phases in building wiring designed for single phase service. He'd be better off to see if the generator can be reconfigured for direct 208/120 service. But if that can be done, it is vmore likely that it can even do double delta (then he gets real 240 volts for line-to-line circuits instead of the wimpy 208 volts).

This is one of the reasons I am planning to divide the circuits in my new house into 3 equally balanced parts. That way, if I ever need to run it on a three phase generator, I can do it more effectively (using 3 480 volt to 120/240 volt transformers). Three 100 amp panels should provide all the power a home needs.

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