3 phase transformer using single phase POTs for 120/240v

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eeee

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I have had a survey done on a set of 3 single phase transformers which make up a 3 phase, 300KVA, 7200 primary, 120/240volt secondary.

My issue is that per my previous research, 3 phase systems are either 480/277volts (line to line, line to nuetral, 208/120 volts.

It is my understanding that single phase systems can be 240/120volts )line to line, line to nuetral), 480/240, 480/277, or 208 (if both legs are connected together)/240.

Can my three phase transformer using a combination of three single phase transformers actually have a secondary made up of 120line-nuetral/240 line-line volts for each of the three phases??
 
Re: 3 phase transformer using single phase POTs for 120/240v

It appears to be a delta w/240v A-B-C and a "lighting tap betweer the A-C which provides the 120/240v with the tap being grounded as you would a common 120/240 1ph, 3w.
a single 3ph transformer is identified as 240/120v 3ph, 4w where a single phase transformer would be 120/240v.
It is also common to use (3) 1ph transformers in a bank with one havng a 120/240v secondary.
 
Re: 3 phase transformer using single phase POTs for 120/240v

Expanding on the 240/120 high leg delta. The voltages line to line are 240V each. The voltages line to neutral are AN = 120V, BN = 208V, and CN = 120V.

This system is very common. It has probably been discussed 4 times in the past month on this forum alone.

Don't make the mistake of saying that three phase systems are ALWAYS something, and single phase sytems are ALWAYS something else, especially on forums that involve a world wide audience. I was just in an industrial plant that had 480delta-240Y/136 drive isolation transformers. And, I recently discussed a ground detection scheme that used a three phase 120V delta connection.

Take a look at a transformer manufacturer's catalog some time and see all of the various standard voltages they offer.
 
Re: 3 phase transformer using single phase POTs for 120/240v

My system is set of Wye-Wye and I should have pointed this out. There are no Delta connections anywhere, so the discussions related to any Deltas will have to be omitted.

It would be appreciated if this sheds any new light related to the fact that it is a wye-wye connection for the three single phase ground mounted aerially distributed POTS that make up the 3 phase, 300KVA, transformer bank system.
 
Re: 3 phase transformer using single phase POTs for 120/240v

eeee,
My system is set of Wye-Wye and I should have pointed this out. There are no Delta connections anywhere, so the discussions related to any Deltas will have to be omitted.
Click to expand...
It is not a wye/wye if the secondary is 120/240.
Don
 
Re: 3 phase transformer using single phase POTs for 120/240v

A wye-wye must be 208/120. A delta could be 240/120 with the lighting tap as mentioned before. What you say makes sense.

There would be no way to wire a 4 wire wye-wye for 240/120. The phase to phase MUST be 208volts.

I can not specify the reading the electric shop reports in my design or it could get connected wrong by the contractor and someone could get hurt. Thanks.
 
Re: 3 phase transformer using single phase POTs for 120/240v

so which is wrong? is it the transformer connection or the voltage? unless there is another lighting or step-up transformer in the system. You should know before proceeding.
 
Re: 3 phase transformer using single phase POTs for 120/240v

Originally posted by jim dungar:


Don't make the mistake of saying that three phase systems are ALWAYS something, and single phase sytems are ALWAYS something else, especially on forums that involve a world wide audience. I was just in an industrial plant that had 480delta-240Y/136 drive isolation transformers. And, I recently discussed a ground detection scheme that used a three phase 120V delta connection.
Click to expand...
And I have been working on a 380/220 volt 3 phase system.
 
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