# Building a Three Phase Transformer.

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#### ikelectro

##### Member
First thing first: Actually my friend facing a problem on three phase transformer that he is building. He called me yesterday to his lab and asked for some help on this. But with my little knowledge on the transformer I was not able to help him and instead I told about this forum. But he requested me to ask here on behalf of him as he does not know English very well (same statement is also applicable for me) . So here is the problem :

Three Phase Transformer | Delta Connection ( in both primary and secondary )

Input = 415 AVC |
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Output = 120 AVC (40 volts in each phase). | this is he wants from the output

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The problem he his facing : while using two phase he is getting approx 80AVC. But when he connected the third phase he is getting 90AVC to 95AVC. according to him that should be approx 120avc.

So can anybody help my friend?

N.B.: Is there any information is needed here? If yes, please let me know.

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##### Well-Known Member
If it is a non-standard values he is looking for, it may be easier just to use three 1ph transformers that may be more available? Connect Star or Delta as needed.
Max.

#### JimB

##### Super Moderator
Output = 120 AVC (40 volts in each phase). | this is he wants from the output
Your understanding of three phase circuits may not be up to scratch.

Three 3phase 40volt outputs do not add up to 120volts, because of the phase difference between the three outputs.

The problem he his facing : while using two phase he is getting approx 80AVC. But when he connected the third phase he is getting 90AVC to 95AVC. according to him that should be approx 120avc.
That does not sound right.
A diagram of how this is connected would help us to understand your (his) problem.

JimB

#### ronsimpson

##### Well-Known Member
Output = 120 AVC (40 volts in each phase)
I do not understand.
When measuring the voltages (Primary and Secondary) are you measuring Phase1 to Phase2 or Phase 1 to Neutral?

#### tcmtech

##### Banned
What does he need it for and to what power level?

As of now what you are saying suggest he wants to have a single phase 120 VAC source that draws from all three phases at once.

#### ikelectro

##### Member
As of now what you are saying suggest he wants to have a single phase 120 VAC source that draws from all three phases at once.
Yes. that is he want. 12o volts from all the three phase outputs.

#### ikelectro

##### Member
I do not understand.
When measuring the voltages (Primary and Secondary) are you measuring Phase1 to Phase2 or Phase 1 to Neutral?
My friend measuring voltages Phase 1 to pahse 2 ....

#### tcmtech

##### Banned
Yes. that is he want. 12o volts from all the three phase outputs.
Is he planing on pulling a huge amount of power or is the source very limited in working capacity?

If he has utility power there is no need to draw evenly off of all three phases unless he is in the high 10's to 100's of KWH demand levels which is very unlikely at 120 volts.

Same with a generator source. Unless his is pulling peak power well beyond 1/2 - 3/4 of its rated KVA capacity there is usually no need to balance the load between all three phases either.

#### RODALCO

##### Well-Known Member
To connect the windings in open delta is not very stable. The reason the voltage goes from 40 to 80 Volts is that it is basically a one phase set up with a 415 Volts primary winding.

Utility practise is three phase delta / star configuration. Don't know why you want delta / delta.
These is a 120 degrees phase shift between phases to take into account.
If you still want to use delta / delta, at least have it in closed configuration and wind the coils accordingly.

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