240 and 480 from same alternator at the same time

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Oregonbythesea

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Hello all, I am new to this site and more of a refrigeration engineer than an electrical guy. However, we are putting together a generator system that will mostly require 460 3 phase power out. There is also some possible times when we will need 240 3 phase power out. We will never need both at the same time. What I want to do is to provide two outlets, one for 3 phase 460 and one for 3 phase 240. The alternator is 12 lead. Can I use those leads and connect them to two different breakers that can't be switched on at the same time to accomplish it? Is there an easier way? Any thoughts, or ideas, would be greatly appreciated.
 
Oregonbythesea said:
Hello all, I am new to this site and more of a refrigeration engineer than an electrical guy. However, we are putting together a generator system that will mostly require 460 3 phase power out. There is also some possible times when we will need 240 3 phase power out. We will never need both at the same time. What I want to do is to provide two outlets, one for 3 phase 460 and one for 3 phase 240. The alternator is 12 lead. Can I use those leads and connect them to two different breakers that can't be switched on at the same time to accomplish it? Is there an easier way? Any thoughts, or ideas, would be greatly appreciated.
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We have built rotary switches for that purpose.
I don't think you can just hook leads to two breakers and get what you want.
 
qcroanoke said:
We have built rotary switches for that purpose.
I don't think you can just hook leads to two breakers and get what you want.
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He's right, it's more complicated than just two breakers, but you will need that too because there will be different amounts of current. The rotary switches could work but how much power are we looking at here? It might be too high for those, but could be done with contactors. That's when you have to start considering just renting a 240V generator.
 
Thanks for what you have both suggested. The problem is, this is a demo unit that will be used for testing. Some of the equipment will be 240 and others will be 480. The amperage will be a max of 50 amps for the 240 and about 25 for the 480. We don't have the space for a transformer. Are rotary switches for this type of load reasonable? One other thing that may clear up this idea. This unit will be a generator for mobile use and will need to have both plugs wired from the 12 leads.
 
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Oregonbythesea said:
Thanks for what you have both suggested. The problem is, this is a demo unit that will be used for testing. Some of the equipment will be 240 and others will be 480. The amperage will be a max of 50 amps for the 240 and about 25 for the 480. We don't have the space for a transformer. Are rotary switches for this type of load reasonable? One other thing that may clear up this idea. This unit will be a generator for mobile use and will need to have both plugs wired from the 12 leads.
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The problem in the way of any simple solution is that even with the 12 leads from the generator all being available, the difference between 240V output and 480V output involves changes in the connections between different sets of those 12 leads as well as external connections to your test loads.
An analogy might help: Suppose you had two 12V batteries and needed to supply (not at the same time) both 12V and 24V loads. For 24V you have to connect the two batteries in parallel, while for 12V you get more capacity if you connect them in parallel. There is no way you can wire up two plugs to the batteries at the same time so that when you connect to one plug you get the batteries in series and when you connect to the other plug you get the batteries in parallel.
That analogy does give us one potential solution, if and only if the generator delivers those voltages with a wye configuration.
Just as you could wire up one receptacle to the series pair of batteries to get 24V and the other to only one of the batteries to get 12V, so you could wire up one receptacle to the center and outside terminals of series pairs of generator windings and the other receptacle to the center point of the wye and to the inner set of wye points from the series string. As with the battery example, you would get only half the current capacity at 240V as you get at 480V instead of twice the capacity. If the generator is oversized enough that would not be a problem.

What are the chances that your 12 lead generator is set up for wye configuration? Not terribly good, but you should find that out first, since it will also affect how difficult it will be to use switches to get the best result.

And BTW, there are rotary switches called drum switches that can handle pretty high current and also complex switching arrangements. (They are often used for motor reversing applications.)
If you have to use contactors to make the power wiring changes, you will almost certainly need more than just two three-pole contactors, and the cost can add up fast. :(
 
I think I have found the solution. Remember, this doesn't have to meet any special code requirements, it is for personal use. 4 double pole, double throw knife switches. 12 leads in and two sets of 12 leads out. Wire after the knife switches to supply 460 to a 25 amp breaker and 240 to a 50 amp breaker. Each breaker is then wired to the appropriate socket. Can anybody see something wrong with this?
 
Oregonbythesea said:
I think I have found the solution. Remember, this doesn't have to meet any special code requirements, it is for personal use. 4 double pole, double throw knife switches. 12 leads in and two sets of 12 leads out. Wire after the knife switches to supply 460 to a 25 amp breaker and 240 to a 50 amp breaker. Each breaker is then wired to the appropriate socket. Can anybody see something wrong with this?
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Four double pole switches do not add up to 12 leads. That does not make me optimistic about the rest of your plan.
Exposed 480 volts on knife switches is just not safe.
 
Oregonbythesea said:
I think I have found the solution. Remember, this doesn't have to meet any special code requirements, it is for personal use. 4 double pole, double throw knife switches. 12 leads in and two sets of 12 leads out. Wire after the knife switches to supply 460 to a 25 amp breaker and 240 to a 50 amp breaker. Each breaker is then wired to the appropriate socket. Can anybody see something wrong with this?
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Besides Star's comment? A couple of points:
You said this is for feeding a demo unit, maybe 480V, maybe 240V. That does not match up with personal use - you sound like you are selling something. Maybe you have plenty of bystanders around while you are demonstrating

You say there is no space for a transformer, but you have space for 4 each 25A (?) - 50 A(?) three pole, double throw, 480V switches? That doesn't make sense.

Just because it is for personal use doesn't mean it does not have to follow code. And, even if you choose to not follow the laws of man, but it still has to follow the laws of physics. And it would be good if you didn't burn yourself and other bystanders to the ground if you threw a switch wrong. 25KW of 3ph 480 is non-trivial

Be that as it may - Have you already bought the alternator? How much of this are you putting together? In particular, did the generator come with a voltage regulator? Did the VR come with the switches, taps, or jumpers to regulate either at 480 or 240?

Don't forget you need cover the grounding and bonding issues. The receptacles will need to be 4wire. You will definitely need an EGC. Be a real bummer, capable of ruining your day, if the gen is parked next to the demo unit and a fault develops, and now the demo unit frame and gen frame have 480V between them.

I'm generally okay with DIY engineering and DIY fabrication.
Oregonbythesea said:
(I'm)more of a refrigeration engineer than an electrical guy.
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Be a really good idea to enlist someone familiar with the safety aspects of 480V generation.

ice
 
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If you have not already bought the alternator yet, there are some other choices - safer, easier to build, easier to operate. And likely no more money

ice
 
I once had a customer that had a 12 lead generator that they did want to be able to configure for about any voltage / number of phases to rent out. I made up some jumper bars that had to be manually configured to change to match the system that was to be supplied. We could supply 120/240 single phase - and get full kVA capacity with a zig-zag connection IIRC or could configure for 208/120, 240/120 three phase, 480/277, and probably some other configurations. But it was complicated enough that they had to have me reconnect it every time voltage needed changed. When you changed especially when going from a wye to a delta or vice versa you did need to tweak the adjustment on the voltage regulator (which I believe adjusted the excitation field of the generator) to get desired voltage.
 
kwired said:
I once had a customer that had a 12 lead generator that they did want to be able to configure for about any voltage / number of phases to rent out. I made up some jumper bars that had to be manually configured to change to match the system that was to be supplied. We could supply 120/240 single phase - and get full kVA capacity with a zig-zag connection IIRC or could configure for 208/120, 240/120 three phase, 480/277, and probably some other configurations. But it was complicated enough that they had to have me reconnect it every time voltage needed changed. When you changed especially when going from a wye to a delta or vice versa you did need to tweak the adjustment on the voltage regulator (which I believe adjusted the excitation field of the generator) to get desired voltage.
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we had a generator (Generac) that had 3 or 4 different boards that we could change out to get the voltage we wanted. Wasn't quick to do. Took at least 15 minutes to change them out.
 
141010-2350 EDT

I do not recomend the method, but I believe that logically 3 DPDT break-before-make switches will change the output voltage This is equivalent a 6PDT switch. Also possibly needed is another synchronied 3PDT switch to the sockets, or totally a 9PDT contactor or drum switch. Each switch pole has to be completely isolated from the other poles.

Study the logic for a while relative to the 3 DPDT switches and see if I am correct.

.
 
Oregonbythesea said:
The generator will be off. KISS
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Yes, my snarky answer deserved a snarky response. You are right, keep it simple. Yes, the switch would only be manipulated when the generator is off. I get that. Shock and death not likely. Much more likely to burn up the generator windings.

On a serious note. I would use molded case contactors here. Haven't used knife switches in decades. Would be trivial to parallel the coils to simultaneously activate the required groups. The whole thing could be activated with one SPDT switch for safety. Molded case contactors are cheap, ubiquitous and much safer.
 
Contactors need a control voltage to operate, which is not present when the generator isn't running, unless you used same voltage as starting battery to power these contactors, but you would still want them to not be powered when generator isn't running to prevent battery drainage.
 
We recently had a vendor bring a demo unit for a process we use. We rented a diesel generator from a yard. I hooked it up, the demo unit need 480V at 30 amps. The generator had
pretty much everything available...120/220, 208 and 480 3P. Why not just do that? I don't know what it cost to rent the thing but for doing equipment demonstrations
it might be easier to just rent what you need at the site.
 
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