Three-Phase Transformer Polarity

[lj]

I am looking at waveforms from a power monitor that show the secondary voltage of a 150kVA three-phase transformer is 180 degrees out of phase with the primary. Does this mean that (a) the transformer is connected wrong, or (b) the transformer polarity dots on the secondary windings are not at the same end as the primary? Thank you.

 

[bob]

I am looking at waveforms from a power monitor that show the secondary voltage of a 150kVA three-phase transformer is 180 degrees out of phase with the primary. Does this mean that (a) the transformer is connected wrong, or (b) the transformer polarity dots on the secondary windings are not at the same end as the primary? Thank you.

Is this a delta - wye transformer? did you check the secondary voltage?

 

[lj]

It is a delta-wye transformer, primary 480V, secondary 220/380V. My main concern if the out-of-phase condition is either harmful or non-NEC compliant. The load is electronic equipment. Thanks.

 

[lj]

And all the voltages measured within 1 to 4 volts of nominal.

 

[jim dungar]

Unless there is some paralleling of 'secondaries', the phase shift between primary and secondary is of no real concern.

 

[iaov]

I'm guessing this apparent phase shift is because of where and how it is being read. Should not be a problem.

 

[ron]

On a delta-wye transformer, the primary to secondary for a regular d-w will have a 30 degree shift.

 

[Pierre C Belarge]

It is a delta-wye transformer, primary 480V, secondary 220/380V. My main concern if the out-of-phase condition is either harmful or non-NEC compliant. The load is electronic equipment. Thanks.

I am not familar with this voltage.
What is it used for?

 

[Pierre C Belarge]

I just googled the voltage. I see it is a 50hz system, used for lab work.
Are there other applications?

P.S.
I see it also should have a 30degree phase shift.

 

[lj]

I haven't seen this secondary voltage until now either. This isolation transformer is in a power distribution unit that supplies power to medical equipment in the US location (60Hz).

 

[mivey]

The wye-delta or delta-wye standard is to have the high voltage 30 degrees ahead of the low voltage. 210 degrees is also used as an alternate connection.

You can get 30, 90, 150, 210, 270, and 330 degrees.

As for concern, see #5.

If you are getting 180 degrees, it sounds like you are comparing an line-line primary voltage with a line-neutral secondary voltage.

Add: and yes, reversing the polarity will get you a 180 degree difference in this case.

 

[lj]

Thanks to all you for your replies. They are very helpful. It sounds like the out-of-phase condition is not harmful and could result from the measurement method. By the way, this transformer is not in parallel with another. Thanks.