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#185985 - 04/09/09 10:27 AM Boost low voltage  
ayrton  Offline
Joined: Dec 2001
Posts: 201
I have a condition where a second floor panel in a server room, is being fed at a distance of roughly 400'.

This panel is controlling sensitive equipment. 208/120v is the system. Reading phase to phase at the 2nd floor panel, is about 198v and phase to ground is about 107v.

This is obviously a problem. IMO it would be less expensive by far to add some buck boosts instead of increasing wire size. It would be 3x as expensive.

Looking at a chart on a website, I see..

Input V 198
Output V 208
Quantity required 2
KVA 45
Load Amps 125
Fuse Size 175

If I am interpreting this right...I need two buck boosts rated each at 45KVA??

What about one AutoWye connection?

My panel is a 125A rated panel.

Last edited by ayrton; 04/09/09 10:33 AM.

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#186004 - 04/10/09 03:57 AM Re: Boost low voltage [Re: ayrton]  
Niko  Offline
Joined: Aug 2006
Posts: 356
Campbell, CA
I found the same specs in my ACME transformer book part # T-1-13075 that cross references with SQUARE-D 2S46F.

Page 114 on this PDF file.

I am sorry but I don't understand your "one AUTO-WYE connection" question?

Be kind to your neighbor, he knows where you live

#186005 - 04/10/09 09:56 AM Re: Boost low voltage [Re: Niko]  
twh  Offline
Joined: Mar 2004
Posts: 918
Regina, Sask.
What would that do to your no-load voltage?

#186007 - 04/10/09 12:59 PM Re: Boost low voltage [Re: twh]  
JBD  Offline
Joined: Jul 2001
Posts: 599
If you want to feed 4-wire loads with your buck-boost you will need to use (3) transformers in a wye configuration.

No one makes a standard single unit for 3-phase buck -boost applications. You must always build your own from multiple 1-phase units. All buck-boost transformers are simply 2-winding transformers field connected into autotransformers.

One problem you will face is that as the load current drops the voltage drop on your circuit also drops. So you may exceed 208Y/120 during no-load conditions.

#186032 - 04/12/09 03:46 AM Re: Boost low voltage [Re: ayrton]  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA


I have a condition where a second floor panel in a server room, is being fed at a distance of roughly 400'.

How about feeding a 45 KVA Transformer in the NER (Network Equipment Room), with a 70 Amp 480V 3 Phase Circuit.
The 125 Amp Panelboard in the NER is fed by the Transformer.

This would eliminate the balancing issues per the use of Boost Transformers.

Seeing that the Building is (at least) 2 floors, with a linear measurement of 400 Feet, it appears likely the Building would have a 480Y/277V 3 Phase 4 Wire Service.

Using this approach would give the NER Panelboard a "Clean" Dedicated feeder, and more control over the Voltage across certain points.
It also removes the Load from another SDS Transformer + Panelboard, making it an independent Load.

If you go the Boost Transformer way, here is a Schematic for connecting (3) Transformers into an Auto Transformer Wye configuration (use this method if Boosting 208Y/120V Circuitry):

Figure #1: 4 Wire Wye Auto Transformer:
* Input: 208Y/120V 3 Phase 4 Wire;
* Output: 229Y/132V 3 Phase 4 Wire.

[Linked Image]

[Linked Image]

To increase the Output Voltage to 244Y/149V 3 Phase 4 Wire, connect the Secondary Windings in Series, instead of Parallel (per the Schematics).
Series connection would be Jumper between X2 & X3 only.

Refer to Voltage Boost Transformers - Wye Connection for more information.

Just for fun, this is an Open Delta Auto Transformer (Voltage Boosting) configuration.
This configuration is only to be used on 3 Phase 3 Wire Circuitry (Single Voltage in/out only)
i.e.: 240V 3 Phase 3 Wire Circuitry.
Do not use for a "Dual Voltage" Circuit - i.e.: 208/120V

Figure #2: Open Delta Auto Transformer:

[Linked Image]

[Linked Image]

This configuration's results:
* Input: 240 VAC;
* Output: 252 VAC.

For an Output Voltage of 264V, connect the Secondary Windings of each Transformer in Series (X2 to X3).

Refer to Voltage Boost Transformer Schematics - Open Delta Configurations for more information.


Scott " 35 " Thompson
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