Single phase transformer sine wave?

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mbrooke

mbrooke

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Reading through a doc about transformers Im confused about the phase shift that takes place between the primary and secondary in a single phase transformers. I always assumed that power coming into the primary of a transformer will be near 100% in phase with the secondary when measured. The oscillograph shows a phase displacement where the primary at its peak means zero potential on the secondary but as the primary begins to fall the field begins to induce a rising voltage in the secondary. Whats the science behind this?
 
mbrooke said:
Reading through a doc about transformers Im confused about the phase shift that takes place between the primary and secondary in a single phase transformers. I always assumed that power coming into the primary of a transformer will be near 100% in phase with the secondary when measured. The oscillograph shows a phase displacement where the primary at its peak means zero potential on the secondary but as the primary begins to fall the field begins to induce a rising voltage in the secondary. Whats the science behind this?
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I don't know where you got that but in over forty years I've never come across a single phase transformer that resulted in a 90deg shift between primary and secondary.
To be blunt, I believe the image to be incorrect.
If I'm wrong, someone better informed that I will shoot me down.

And welcome to the forum BTW.:D
 
:thumbup:
There is often confusion when somebody mistakenly shows a current waveform instead of a voltage waveform on one side.
1. The load current will exactly cancel the magnetic field of the primary current associated with it. (Subtract out the magnetizing current.)
2. The voltage with no load will be 90 degrees out of phase with the no load current. But that current will in turn be 90 degrees out of phase with the applied voltage.

Tapatalk...
 
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Besoeker said:
I don't know where you got that but in over forty years I've never come across a single phase transformer that resulted in a 90deg shift between primary and secondary.
To be blunt, I believe the image to be incorrect.
If I'm wrong, someone better informed that I will shoot me down.

And welcome to the forum BTW.:D
Click to expand...


Thanks for the reply! :D

The oscillograph is from this transformer theory pdf:

http://www.nfphampden.com/xftheory.pdf
 
mbrooke said:
Thanks for the reply! :D

The oscillograph is from this transformer theory pdf:
Click to expand...
It isn't an oscilligraph.
It's a sketch probably done in some drawing application.
And it really isn't a terribly good representation.

This an actual measured and sinewave.



And the 120V-0-120V relationships.

 
Those aren't oscillographs. They are illustrations. They aren't even sine waves. They are end-to-end half ellipses.
 
mbrooke said:
No clue. But that's what the pic is saying. But I have to agree with the others it has to be wrong.
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The reference to "360 electrical degrees" in the caption makes me suspicious of the whole table. Maybe even the whole paper. :)

However, looking at the rest of the paper, it is possible that although they show 120/240 single phase 3-wire, they are illustrating the output of one phase of a delta-wye transformer. Unfortunately that could produce a 30 or 60 degree phase shift, not 90. Vector group Dy3 does not exist. :)
 
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