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Buck Boost Transformers / 3 Phase using 2 Single Phase Buck Boost Transformers

Jpflex

Electrician big leagues
Location
Victorville
Occupation
Electrician commercial and residential
Hey guys, I have looked all over the forum and beyond for help on buck boost wiring. I believe I have an understanding of Single Phase Buck Boost Transformers but when I try to apply the math to a 3 Phase System. I am not coming out with numbers that make sense. I hope that the forum community can shed some light.

I do have a specific question in mind but I'd like to ask a general question to help me, and hopefully others, grasp the method of bucking or boosting a 3 phase system to a different 3 phase voltage using 2 Single Phase Buck Boost Transformers. This may be the key for my other question and probably the rest to come.

The photo attached is one of the wirings in question.

According to this diagram, I will get 208V between A+B and B+C but not A+C. Does that sound correct?

For example, I have 218V Input and I want a 208V Output. This wiring configuration only drops voltage on A and C Leg.

I cannot run a 208V 3 Phase Equipment with significantly lower voltage between the A+C Leg . Yet, this is the diagram I was referenced to from the Buck Boost Transformer.
I believe my math or my understanding..or both... is incorrect somewhere.

I've attached a photo of the nameplate of the transformer to assist with any info.

I'd appreciate any help.
I installed 2 boost transformers once sourced from a delta delta ungrounded 300KVA, 4800/480 volt 3 phase transforber.

The boost transformer stepped up the 480 volts to 575 volts for a specific motor set up. I remember having to hook up a jumper between both boost transformers but although it was confusing at first, my first wiring attempt was correct

The second diagram in your post makes sense except the last part where putting the secondary windings in parallel X3 to X1 and x2 to x4 which the diagram show to yield a higher voltage?

The opposite should be true since there are less series windings in boost rotation direction and less voltage impressed across each individual coil loop why then does it show a secondary boost effect?

When the primary windings are placed in parallel it is for a smaller voltage input as expected?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
When the primary windings are placed in parallel it is for a smaller voltage input as expected?
Yes. The dual 120v primaries are wired in parallel for 120v and in series for 208v to 240v.

The dual 12v (or 16v) secondaries are wired in parallel for 12v (to 16v) boost or buck, and in series for 24v (to 32v) boost or buck (adjusted for voltage actually applied.)
 

Jpflex

Electrician big leagues
Location
Victorville
Occupation
Electrician commercial and residential
The dual 12v (or 16v) secondaries are wired in parallel for 12v (to 16v) boost or buck, and in series for 24v (to 32v) boost or buck (adjusted for voltage actually applied.)
That’s actually my point how is the secondaries put in parallel yielding a higher voltage than if they were placed in series?

A series connection with windings at the proper orientation will allow more volts impressed across each individual winding loop series addition?
 

FlyWhale

Member
Location
NC
Occupation
Electrician
Hey ya'll I know its been a few days. You guys are teachers and I learned something new about transformers today. Thank ya'll.
 

kwired

Electron manager
Location
NE Nebraska
Occupation
EC
I installed 2 boost transformers once sourced from a delta delta ungrounded 300KVA, 4800/480 volt 3 phase transforber.

The boost transformer stepped up the 480 volts to 575 volts for a specific motor set up. I remember having to hook up a jumper between both boost transformers but although it was confusing at first, my first wiring attempt was correct

The second diagram in your post makes sense except the last part where putting the secondary windings in parallel X3 to X1 and x2 to x4 which the diagram show to yield a higher voltage?

The opposite should be true since there are less series windings in boost rotation direction and less voltage impressed across each individual coil loop why then does it show a secondary boost effect?

When the primary windings are placed in parallel it is for a smaller voltage input as expected?
Was they basically 480 x 120 power transformers connected as autotransformers?
 
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