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#205927 - 04/27/12 04:49 PM Transformer/engineering question  
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,317
Alaska
I have a situation where I need to power a intermittent single phase large load with a three phase transformer so I will not be using one leg. Its short term hook up for two to three years at best so I do not want to buy a transformer ($$$$$) when I have a 3 phase dry transformer collecting dust of sufficent size. I have not come up on this type of config before so I have my conserns. Such as

*Would it be kosher to wire and tap only two of the three coils?

*if not, what issues would I have if I were to wire the high side 3 phase and only use two legs where the amperage in theory be upto 100 amps, 90 more realistically and only intermittenly?


"Live Awesome!" - Kevin Carosa

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#205928 - 04/27/12 07:45 PM Re: Transformer/engineering question [Re: sparkyinak]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,808
Brick, NJ USA
I've seen this done over the years, as having 3 phase wired as normal, secondaries going to a disconnect/panel, and single phase load being connected.

Can't say I heard of any problems.

IMHO, as long as the xfr is of sufficient KVA, you should be OK. Efficiency? May be an issue.

Scott....jump in here please!


John

#205931 - 04/28/12 02:35 PM Re: Transformer/engineering question [Re: sparkyinak]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
Does the transformer have each end of the secondaries available for separate connection? If so, you could hook them up in a "dog leg" connection to get single phase out of a three phase source.

It is the same method that is used on three phase generators when they need to supply single phase loads.


#205932 - 04/28/12 03:00 PM Re: Transformer/engineering question [Re: LarryC]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
I timed out while editting. Use the following "Scott" drawing.

12 lead generator drawings

Basically it is a open delta where Phases A & B are connected in opposing series and Phase C is connected in aiding series to the combined A & B. The output "L1"is connected to the free end of A, the "neutral" is the connection between B & C, and "L2" is the free end of C. The connection between A & B is not used.

This limits the unit's maximum power to 2/3 of full rating but is does load the 3 phase input equally.

Larry C


#205939 - 04/29/12 07:32 PM Re: Transformer/engineering question [Re: LarryC]  
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,317
Alaska
I am not sure if it's a 12 wire transformer or not. I currently do not have access to it.

Larry, I think the the 12 lead generator link is hinky. It takes me to some web site. I do have schems of generators and I didn't thInk of looking at it from your perspective.

Thanx for everyone's input


"Live Awesome!" - Kevin Carosa

#205940 - 04/29/12 10:12 PM Re: Transformer/engineering question [Re: sparkyinak]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,069
Estero,Fl,usa
Maybe I am missing something but why not terminate in a 3 pole disconnect and feed a single phase panel from there or just use a 3p panel with one 2 pole breaker plugged into it.

The transformer won't care.


Greg Fretwell

#205944 - 04/30/12 12:52 AM Re: Transformer/engineering question [Re: gfretwell]  
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,317
Alaska
That is what I'm planning to do. By maxing two of three legs while having nothing on the third leg, I dont know such an unbalance would cause any issues for the transformer and or the circuits or not. That would be a rather expensive smoke test if overlooked something


"Live Awesome!" - Kevin Carosa

#205947 - 04/30/12 12:20 PM Re: Transformer/engineering question [Re: sparkyinak]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
The link is hinky because address got changed from electrical-contractor .... to electrical.contractor ....

The link is supposed to go to the technical drawings on this site.

Larry


#205949 - 04/30/12 05:41 PM Re: Transformer/engineering question [Re: LarryC]  
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,317
Alaska
Ah ha! That did it. Thanx Larry.

Btw, I'll get the rest of my barge pics posted some day. Got super busy. Finally getting on top of things.


"Live Awesome!" - Kevin Carosa

#205950 - 04/30/12 05:45 PM Re: Transformer/engineering question [Re: sparkyinak]  
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,317
Alaska
And nice drawings Scott


"Live Awesome!" - Kevin Carosa

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