Reverse transformer

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Andy1099

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Location
jackson wy USA
[FONT=&quot]We have a 208 volt 3 phase grounded service and are installing a transformer to get 480 volt 3 phase for a piece of equipment. It would seem to me we would still need to have a Grounding Electrode Connection on the 480 side of the transformer. Is this correct? The 480 volt 3 phase feed will land I on overcurrent device-a breaker. How is the proper way to ground this transformer? I am being told the GEC needs to connect to the transformer case and EGCs but that does not seem correct to me. [/FONT]
 

GoldDigger

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Location
Placerville, CA, USA
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The 480V secondary can supply an SDS that is ungrounded, but there are limitations, including provision of a ground fault detector, that go along with that.
The other options are to provide a low or high controlled resistance ground through a zig-zag transformer or to simply ground one of the 3 wires, producing a corner grounded system.
Some loads will not tolerate a corner grounded system.
Others will not tolerate an ungrounded system, and certain types of fault can put more than twice the nominal voltage across wire and load insulation to ground.
You need to understand the three options and how they interact with your loads.

Sent from my XT1585 using Tapatalk
 

ActionDave

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Durango, CO, 10 h 20 min from the winged horses.
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[FONT=&quot]We have a 208 volt 3 phase grounded service and are installing a transformer to get 480 volt 3 phase for a piece of equipment. It would seem to me we would still need to have a Grounding Electrode Connection on the 480 side of the transformer. Is this correct? The 480 volt 3 phase feed will land I on overcurrent device-a breaker. How is the proper way to ground this transformer? I am being told the GEC needs to connect to the transformer case and EGCs but that does not seem correct to me. [/FONT]

What kind of transformer are you using? An off the shelf step down transformer wired up backwards or a step up transformer?
 

infinity

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Staff member
Location
New Jersey
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What kind of transformer are you using? An off the shelf step down transformer wired up backwards or a step up transformer?

That's what it sounds like to me. We always corner ground when using those. When you look at Diggers different scenarios it might be better to just get a Delta-Wye step up transformer and eliminate any potential problems.
 

Besoeker

Senior Member
Location
UK
That's what it sounds like to me. We always corner ground when using those. When you look at Diggers different scenarios it might be better to just get a Delta-Wye step up transformer and eliminate any potential problems.
That's what I would do. It may have to be custom made rather than off the shelf but may not be more expensive given that you can specify the rating required rather than the nearest size above.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
That's what I would do. It may have to be custom made rather than off the shelf but may not be more expensive given that you can specify the rating required rather than the nearest size above.


Transformers that are delta on the 208V side and wye on the 480/277V side are commonplace.
 

Besoeker

Senior Member
Location
UK
Transformers that are delta on the 208V side and wye on the 480/277V side are commonplace.
For you guys possibly.........:p
But then you have all those weird wired voltages!
120, 208, 240, 277, and 480 not to mention high leg delta.....

Kungfuzing for a simple Scotsman.
LV here is 400V three phase from which 230V phase to neutral is derived for domestic/commercial. It really is that simple. Home and office appliances are designed for that although some things like power supplies for laptops, printers, phone chargers etc. can usually take quite a wide range to cater for international markets.

Mods, forgive my frivolity.........I just like it simple...............:D
 
For you guys possibly.........:p
But then you have all those weird wired voltages!
120, 208, 240, 277, and 480 not to mention high leg delta.....

Kungfuzing for a simple Scotsman.
LV here is 400V three phase from which 230V phase to neutral is derived for domestic/commercial. It really is that simple. Home and office appliances are designed for that although some things like power supplies for laptops, printers, phone chargers etc. can usually take quite a wide range to cater for international markets.

Mods, forgive my frivolity.........I just like it simple...............:D

We won the war....we can make our electrical system as complex as we want :p
 

norcal

Senior Member
For you guys possibly.........:p
But then you have all those weird wired voltages!
120, 208, 240, 277, and 480 not to mention high leg delta.....

Kungfuzing for a simple Scotsman.
LV here is 400V three phase from which 230V phase to neutral is derived for domestic/commercial. It really is that simple. Home and office appliances are designed for that although some things like power supplies for laptops, printers, phone chargers etc. can usually take quite a wide range to cater for international markets.

Mods, forgive my frivolity.........I just like it simple...............:D

You did not have legacy systems to contend with. :p
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
Just had a project that got the forum's help for the correct transformer. Ended up removing the 240delta-480delta transformer and using a reverse fed transformer 240V delta to 480-277 wye. Much easier than dealing with the corner ground and ground fault alarms set up.
 

Besoeker

Senior Member
Location
UK
Just had a project that got the forum's help for the correct transformer. Ended up removing the 240delta-480delta transformer and using a reverse fed transformer 240V delta to 480-277 wye. Much easier than dealing with the corner ground and ground fault alarms set up.
Excellent. And I apologise to the forum, including the mods, for getting side tracked.................:D
 

rhamblin

Senior Member
So I came here looking to find if it was legal to owire a transformer backwards.

So I came here looking to find if it was legal to owire a transformer backwards.

Is it, obviously it will work, but is it legal? I was at a plant recently that I encountered a 120/240 volt switchgear/service feeding through OCPD and then run backwards through a 277/480Y to 240 volt delta xfmr. Is this legit?
 
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