120/208 to 120/240 volt buck and boost transformer

[desertdude59]

At work I am going to install two 120/240 buck and boost transformers that will feed a 3 phase 150 amp breaker for a CNC machine. It's going to be fed with 120/208 from an MDP. The primaries on the B&B are 120/240 and the secondary's are 12/24. Now looking at my prints it a delta Y without a neutral. I've never had to hook up a transformer like this. I'm used to the normal transformers with taps. Is this even possible? The damn super put me on the spot so I'm not even sure if I can make this work with the B&B that the office sent out.

 

[GoldDigger]

A delta to wye would not technically be a boost but rather an isolation transformer with a close to unity ratio.
You can do a true boost with a wye input with no problems, but working from a delta input on a corner grounded system produces really odd output voltage and phase combinations.
The other problem with your initial statement is that you cannot have a 240Y/120 three phase system, so it is a little hard to understand what your boss is expecting to get.

 

[ActionDave]

At work I am going to install two 120/240 buck and boost transformers that will feed a 3 phase 150 amp breaker for a CNC machine. It's going to be fed with 120/208 from an MDP. The primaries on the B&B are 120/240 and the secondary's are 12/24. Now looking at my prints it a delta Y without a neutral. I've never had to hook up a transformer like this. I'm used to the normal transformers with taps. Is this even possible? The damn super put me on the spot so I'm not even sure if I can make this work with the B&B that the office sent out.

It looks weird because you are tying the primary and secondary of the B/B transformers together. If you follow the connection diagrams it will work fine.

 

[kwired]

Does your output side need to have a neutral conductor? If so you need to scrap the buck boost idea and use an separately derived system.

If your output doesn't need a neutral but still needs a neutral potential to ground then you still likely need to use a separately derived system.
One reason for this may be the MOV's protecting a drive or other component can't take too high of a voltage to ground and must be connected to a grounded wye source.

But I looked again at OP and appears that he is trying to go from 208 to 240, You will not find a 240 volt system (three phase) that doesn't have at least one conductor more then 120 volts to ground

 

[kwired]

Even if you are using different brand of transformers, go to the following link and enter data for your application. It will tell you what unit you need and how to connect it. Just use same size and type for the brand you are using if it is different.

http://www.buckboostcalculator.com/

 

[desertdude59]

I appreciate all of your help. We looked at the diagram and it is possible. At first we decided to set 3 transformers- 1 for each leg. Upon further investigation my boss said that it is possible to use the 2 transformers. I just have never had to wire these B&B transformers like this. I'm just going to have to use Square D's wiring diagram for the correct voltage. They have me so busy at work I haven't even had time to set up the panel, transformers, and gutter can.