3 Phase to 1 Phase Transformer

Your post is a little hard to understand. You say the primary is delta. It realy does not matter. What is needed is

1. What is the secondary voltage?

2. The secondary could be wye or delta. Which is it?

3. What is the load current normally on the UPS?

Your documents are very good - well answered with the vector diagram and calculations. GA from me.

- MS

this is a "Open Delta " connection

http://cr4.globalspec.com/thread/55606,

I started a thread about 3 to 1 phases transformer and I got very helpful comments, you can check

Dear all,

Yes, it is a sort of open delta connection.

Normally, open delta is used 3 phase to 3 phase conversion using two 1 phase transformers.

The subject of this thread is a 3 phase to 1 phase transformer, and the secondary connection is inverted against primary. This connection is not same as 3phase-3phase open delta.

Regards

Open Delta connection could also be used for single phase application at secomdary,

you have to calculate the correct ratio of the transformers.

I already use it, and current distrubution over the 3 phases at primary is 1-2-1

Regards

Do you mean Scott connection? If so, the further question is: How do we provide earth fault protection? Simply sum up all three phases to get residual current as earth fault?

No

Scott configuration output is 2 phases 90 deg phased and more complicated

Just an Open Delta

for the earth fault current you can earth one end at the secondary side and use any usual fault detection method

when input is balanced, opendelta output will be showing zero volt isn't it? Does this transformer adopt different voltage ratios for different phases in order to achieve output voltage across open delta? How do you explain Y phase current is double of other two phase currents on primary side? In such cases, how do we adopt earth fault protection? Will the summation of all three phases in primary be still zero? Because, primary currents will be displaced by 120 degree. In order to make sum of three currents to zero, R & B phase currents should be co-phasal and 180 degree out of phase to Y phase current. Can I get a vector diagram?

http://cr4.globalspec.com/thread/55606,

Check this thread, I initiated an I got valuable replies from forum members.

there you will find answers to your questions

Dear Le_Noble, Thanks a lot for the reply. It clears my doubt... output is V connection and not open delta. Because, open delta calls for three phases which means sum is zero under balanced condition. Here it is two phases so sum is Line voltage. Now the question remains ... how to provide earth fault protection for the primary side when branch point of Y phase (middle phase) connection is not accessible outside.