208/120, 3 phase Buck Boost Transformer

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The 'Buck and Boost' transformer will give you correct line-line voltages, but will create a system with heavily unbalanced line to ground voltages.

This is often perfectly acceptable, for example supplying power to an 'across the line' started induction motor.

This can also be a big problem for some loads if there is a line-ground reference in the load. One common situation is when VFDs are used; the input to the VFD often has ground referenced transient voltage suppression, and this will be unhappy with anything other then a wye supply.

If the manufacturer has specifically given the okay to the use of the buck and boost transformer, then it should work just fine.

-Jon
 
To add to my post:

winnie said:
If the manufacturer has specifically given the okay to the use of the buck and boost transformer, then it should work just fine.
Click to expand...

You mention a 'CNC table', which almost certainly means an expensive device run with drives. I would be sure to double check the communications with the manufacturer. In the title of this thread the OP mentions 'buck and boost' transformers. In post #6 the OP states "I am asking about a 3 phase isolation transformer".

If the manufacturer permits an isolation transformer, and the OP installs a buck and boost transformer, then there could be problems.

-Jon
 
winnie said:
To add to my post:



You mention a 'CNC table', which almost certainly means an expensive device run with drives. I would be sure to double check the communications with the manufacturer. In the title of this thread the OP mentions 'buck and boost' transformers. In post #6 the OP states "I am asking about a 3 phase isolation transformer".

If the manufacturer permits an isolation transformer, and the OP installs a buck and boost transformer, then there could be problems.

-Jon
Click to expand...
This is what I received from the manufacturer:
"Regarding the buck boost, I was told that and Autotransformer that will scub off 24V will be best. You can get them at Automation direct, anything on there will do or the brand Acme."
Reviewing the company he mentioned, I did not see anything compatible. He said that as long as the high leg is installed in position C all will be good.
 
"Anything on there will do" isn't particularly helpful. You need to select based on required voltage change and load current.

This is the category; there are loads of choices:

The Larson part you posted is also a fine buck/boost.

You never specified the current your load requires.

-Jon
 
winnie said:
"Anything on there will do" isn't particularly helpful. You need to select based on required voltage change and load current.

This is the category; there are loads of choices:

The Larson part you posted is also a fine buck/boost.

You never specified the current your load requires.

-Jon
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The equipment requires 220V 60AMP 3 Phase. My existing equipment "averages 246V line to line with B phase at 212V.
 
The Larson component you selected should work fine with those current requirements.

A pair of these should also work:

I'd suggest before proceeding on the basis of internet suggestions you read through and understand the 'selection tables' for buck-boost transformers, for example:


or


Buck/Boost transformers are really isolation transformers _connected_ in an autotransformer configuration. You are working with standard off the shelf transformers. These transformers are usually available with a 120/240V or 240/480V primary, and various secondary ratings, eg. 8/16V, 12/24V, or 16/32V.

After you read the selection tables, you will likely be pointed at a transformer configured for 240V primary and 24V secondary, and the selection table will suggest a configuration that will convert your 246V supply to 224V. A slightly less efficient connection will let you take your 246V down to 221V. You could also select a 32V transformer and take your 246V down to 217V. Without custom transformers you won't get to exactly 220V; you will need to evaluate the tolerance on the 220V number.

After you read through the selection tables, come on back if you have any questions.

-Jon
 
AJones said:
This is what I received from the manufacturer:
"Regarding the buck boost, I was told that and Autotransformer that will scub off 24V will be best. You can get them at Automation direct, anything on there will do or the brand Acme."
Reviewing the company he mentioned, I did not see anything compatible. He said that as long as the high leg is installed in position C all will be good.
Click to expand...
They likely won't have a single unit that is for three phase in the autotransformers. You need to purchase two single phase units and interconnect them in an open delta configuration to buck/boost three phase. Many others out there are same way. Most will have selection information and connection diagrams on the site to do this. Automation Direct has a excel spreadsheet you put application information in and it will tell you what unit(s) you need and how to connect them.
 
AJones said:
The equipment requires 220V 60AMP 3 Phase. My existing equipment "averages 246V line to line with B phase at 212V.
Click to expand...
from the spreadsheet available for the Acme transformers via Automation Direct website:
1671199427741.png1671199390837.png
As mentioned output may not be exactly 220 but will be pretty close, so pay attention to tolerances if they are tight.
 
kwired said:
from the spreadsheet available for the Acme transformers via Automation Direct website:
View attachment 2563243View attachment 2563242
As mentioned output may not be exactly 220 but will be pretty close, so pay attention to tolerances if they are tight.
Click to expand...
I returned from vacation, and they installed 2, T113073 instead. I was reviewing the selection chart and I am not comfortable with the voltages that are indicated. Can you ease my troubled mind before I make them return these?...
 
The T113073 is a 1kVA 240:16/32 transformer.

Two of them will buck your 246V to 217V with 31A capacity (too small for the 60A rating)

They could also be configured to buck 246V to 230V with 62A capacity, which is sufficient current capacity if the voltage isn't too high.

Jon
 
winnie said:
The T113073 is a 1kVA 240:16/32 transformer.

Two of them will buck your 246V to 217V with 31A capacity (too small for the 60A rating)

They could also be configured to buck 246V to 230V with 62A capacity, which is sufficient current capacity if the voltage isn't too high.

Jon
Click to expand...
That's the CC configuration, correct?
 
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