Transformer Question?

[dduffee260]

We have a building that was previously 240/120 3 phase. We upgraded the service to a 208/120 wye system. The engineer called for a 208 delta to 240 wye transformer to be installed. Square D does not make a 208 delta to 240 wye transformer that I can see. If we simply run the neutral from the 208 switchboard to the 240 panel what is the issue? The lighting loads are the only neutral loads on the smaller panel. They total about 30 amps on an 800 amp panel. Does anyone see a problem with simply carrying the neutral wire thru the transformer to the 800 amp panel?

 

[BAHTAH]

240V wye??

240V wye??

We have a building that was previously 240/120 3 phase. We upgraded the service to a 208/120 wye system. The engineer called for a 208 delta to 240 wye transformer to be installed. Square D does not make a 208 delta to 240 wye transformer that I can see. If we simply run the neutral from the 208 switchboard to the 240 panel what is the issue? The lighting loads are the only neutral loads on the smaller panel. They total about 30 amps on an 800 amp panel. Does anyone see a problem with simply carrying the neutral wire thru the transformer to the 800 amp panel?

If I am reading your post correctly it sounds like you are trying to supply some 120v loads that are in an existing 240/120 3ph4w panel. You could install a single-phase transformer and a small single-phase panel for those loads or install a 120/208 3ph4w panel and not use a transformer and move the 120v loads to the new panel.

 

[jim dungar]

You can not use the neutral of the primary to supply line-neutral loads on the secondary.

And yes, you can get 208-240Y transformers (look in the drive isolation section of catalogs). But, the line-neutral voltage will be 138V which I am sure will not be compatible with your 120V loads.

Square D and other manufacturers do make 208-240/120 3PH 4W transformers.

 

[ron]

You need approx a 425kVA boost (buck/boost style) transformer. At this size it will be custom order.

 

[iwire]

If we simply run the neutral from the 208 switchboard to the 240 panel what is the issue?

The issue is you would be trying to use a neutral from one source with the ungrounded from another source.

Picture two 120 volt generators side by side with no electrical connections between them could you get a usable 120 volts by running a hot from one and the neutral from the other?

 

[hillbilly1]

We have a building that was previously 240/120 3 phase. We upgraded the service to a 208/120 wye system. The engineer called for a 208 delta to 240 wye transformer to be installed. Square D does not make a 208 delta to 240 wye transformer that I can see. If we simply run the neutral from the 208 switchboard to the 240 panel what is the issue? The lighting loads are the only neutral loads on the smaller panel. They total about 30 amps on an 800 amp panel. Does anyone see a problem with simply carrying the neutral wire thru the transformer to the 800 amp panel?

If the 120 volt loads only total 30 amps, the engineer should have stayed with the 120/240 delta service, If 120/208 WYE was needed for some odd loads or just that smaller panel, a 240 volt delta to 120/208 WYE transformer of appropriate size should be used. Are the exsisting three phase loads rated for 208 or 240 volts? Many RTU's are dual rated , but the control transformers inside them must have the taps changed to the appropriate voltage.

 

[frenchelectrican]

I have a hunch but I may be wrong on this part but I do belive the POCO have guideline when you upgrading the 3? 4W delta system to Wye system and most POCO will not upgrade the delta system anylarger than have to.

Myself and Jim Dungar have same POCO plus WPS both POCO mention they will use the exsting delta but sized the transformer to the main breaker size but nothing more unless approved by POCO engineers

And any new customers get new 3? service will only get wye format reguardless of size { med and high voltage customers may have slighty diffrent situation to deal }

That how many POCO is slowly getting rid of delta service.

Merci,Marc