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Old 03-04-2011, 08:38 AM   #1
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Three phase transformer question


Okay guys, I realise this is a little beyond the scope of what most do-it-yourselfers do but...

Here is what I need: I have a large home workshop that I will use for a variety of things including buying and refubishing surplus power equipment.
Some of the items will be permanently installed for example, a 10HP 3-phase air compressor, a 480V 3 phase parts washer (I currently have this) and a mix of other single and three phase appliances.

My utility company has given me several options including 480v/277v wye with a total of three transformers required. I was told that I could use one of the existing pole mounted transformers and just had to purchase two more. I am thinking that the 480/277 is the best option with a 75 amp @ 480v service entry to the building.

I know I can take one phase of the 480V (277V) for my lighting. I plan to run all my flourescent ballasts on this. However, in addition to the 480V
which I can run my compressor and parts washer on, I will need 240V single phase, 120V single phase and 208 v three phase.

I know that reduced voltages can be attained with dry transformers. This is where it gets tricky for me. I found a good deal on a 30KVA 480v in 208/120 v out unit that will take care of my 208 and 120 needs this covers everything except the 240 single phase requirement.

Will I need to buy a second transformer to convert 480v three phase to 240 single phase? Transformers aren't cheap is there a wiring trick someone can tell me about? Or can anyone recommend a tranformer that will provide 208V three phase, and 120 and 240 single phase.

Thanks

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Old 03-04-2011, 05:22 PM   #2
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Three phase transformer question


How many different voltages do you need.

If you have 480 volt 3 phase, you can get a single transformer that connects across two of the three phases to give you 120/240 volt single phase.

You can get a setup (either a single transformer or three) that takes 480 volt 3 phase (277 volt legs) and gives you 208 volt 3 phase (120 volt legs)

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Old 03-04-2011, 09:50 PM   #3
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Three phase transformer question


How hard was it to get your utility company to agree to 480v 3 phase power?

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Old 03-05-2011, 02:55 AM   #4
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Three phase transformer question


I am kinda suprised that your POCO will give you a option of 480Y277 system in your resdnetial I hope that your workshop is comeplty detached and have zoned for commercal then that is only legit way it can get that high a voltage.

I have alot of experice with triphase system IMO the cost of breaker and other stuff are much higher than what you can get them in standard monophase or triphase at 208Y120 volts { just keep in your mind most POCO will NOT give out 240 volt delta anymore for safety reason I will discuss that later if you are instering }

IMO it much cheaper just get 208Y120 volts I know the air compressor motour can run on 208 without major issue I have one customer he have 20 HP air compressor on 208 volt triphase with out issue (the motor is rated to work both 208 and 240 volt system )

You can have 200 amp triphase at 208Y120 volt and how big that part washer { give me the nameplate @ 480 volts I will figure out the conversation to 208 }

This 208Y120 system is much safer than 480Y277 is and I have 480 volts in my shop but have a transfomer to kick down to 208Y120 for both shop and house

The other reason why I suggest to stay 208Y120 system is that you do not have to worry about the transfomer issue at all.

The smallest 480Y277 main breaker size you can get IIRC is 100 amp but 200 amp is pretty common but there is addtional POCO rules on them so the POCO and electrician will have to fill you in with their latest regulations on that.

with your statement you say 75 amp @ 480 volts that will not get you very far with it unless the POCO say 75 KVA that is diffrent story on rating the 75KVA @ 480 volts will draw about 90 amp max.

You can get away with smaller conductor size however what will get ya is the cost of breaker and fuse at 480 volt will cost more than what you can do on 208 side so I am seriously recomeoned have a electrician to assist you if you stick with 480 volts system there is a bit of rules to cover which they don't really apply to 208 much in someway.

The 30 KVA 480/208Y120 transfomer is ok they are rated about 83 amp on secondary side so that is ok with not hevey loaded items that should take care of some of the lights in your office or bathroom and genral receptale circuits.

The other thing will come in play in here is colour codes as well you will need more colour conductor than what you will need at stragiht 208 system.

Quite few items what work on 240 volts monophase will work on 208 I know water heater for sure no question but take little longer to heat up but single phase motour that may be a toss up depending on the nameplate { if they stated to run on 208 then it will be fine }

I will stop right there for now unless you have more question to ask in here.

I am well verised with both European sytem and Americané system.

Merci,
Marc

{ my shop I mention that in the staté but in France it is 415Y240 volts I will leave this part out for now }
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Old 03-07-2011, 04:54 PM   #5
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Three phase transformer question


Marc, you said if you are interested that you would explain why the 240 delta is not installed, I am not the OP but I am interested in an explanation.

Last edited by WDR; 03-07-2011 at 08:26 PM.
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Old 03-07-2011, 08:08 PM   #6
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Quote:
Originally Posted by WDR View Post
Nap, you said if you are interested that you would explain why the 240 delta is not installed, I am not the OP but I am interested in an explanation.
That was Marc...
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Old 03-07-2011, 08:28 PM   #7
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Three phase transformer question


Well Thanks for reminding me, I was just reading a post by Nap.
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Old 03-08-2011, 01:39 AM   #8
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Marc, you said if you are interested that you would explain why the 240 delta is not installed, I am not the OP but I am interested in an explanation.
Sure I will be glad to expain why due more and more POCO's will not install delta system any more due one is wild leg which if you mesure the voltage from line to netural and I Know you are famauir with common single phase voltage system ok so far you are fine but just think of triangle and from netural to wild leg the voltage is useally 208 volts some case 190 will show up as well.

So therefore with wild leg hookup if you have anything on 120 volts that connected to wild leg it will make magic smoke no question asked { I have see that too many time when someone not pay attetion to the connection basically the same way with single phase when they loose or someone lifted the netural }

The other reason that is the safety issue with the breaker ratings as well they will use the straight voltage rated breaker which typically cost more and some case it can be backorded for a bit so that is the other part will affect it.

I do keep couple stright voltage breakers on hand and they are not cheap { typically 3 to 5X over the convental breakers }

And the other thing some peoples may not be aware with old delta system they will have red conductors but the modern are orange in colour.

Not only many DIY'ers are not really aware with delta system and some electricians are not famuair as well but pretty good percentage will understand it.

I will show you the diagram it will clear up this part

That will show 4 wire Delta system and there is 3 wire delta system that will be grounded or not { this part is mainaly used for motour loads }

The Wye connection is far more common and safer to use.

Hope that help you on this one.

Merci.
Marc
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Old 03-08-2011, 07:19 AM   #9
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Three phase transformer question


Thanks for explaining, I think I understand how it works now.

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