Not exacty, though I do beleive that we are all students that will continue to educate ourselves through experience. I'm just a fellow with an instrumentation background caught in a power setting. I've got a customer that has done what I have described above on a 3 phase transformer with taps. I'm not sure if the transformer was loaded or not, but it was intended to run a motor. By doing this, the tansformer imediately shut down. The C phase winding was telescoped and the taps in the other two windings seem to have hardwired themselves in its maximum setting.
Do you mean that someone swapped the H1 and H3 cables? Because besides reversing the phase polarity on the output, nothing else should happen.
What you describe as 'telescoped' windings usually indicates an internal fault.
Can you explain what was done a little better?
I have not yet recieved a complete expaination, but from what I understand, the cables were swapped and the unit imediately shut down. All of my research has pointed to reverse polarity on the output as well.
I'm not exactly sure what that means.
The nameplate of a delta-wye transformer will show the vector diagram for the H1, H2, H3, and X0, X1, X2, & X3 connections.
I don't know what the unit stickers are.
Again, just swapping the H cables around on the H terminals will not cause a fault. (Swapping any H to X leads will!)
When you say it immediately shut down, I'm assuming a C/B or a fuse opened, and there was some noise/arcing in the transformer, etc?
Can you explain "the taps in the other two windings seem to have hardwired themselves in its maximum setting" better? Usually, a transformer will have five taps (one for nominal voltage, two above and two below nominal)which are adjustable for each coil by means of a jumper wire. What size transformer and what voltages are we dealing with?
What voltages is the transformer name-plated for? Is it a dry-type transformer or a liquid filled transformer? Hopefully the leads weren't swapped while the transformer was energized, so what would immediately mean? When did immediately happen?
If you swap inputs to H1 and H3 on a delta-wye transformer, two things will occur:
1. Phase sequence will be opposite. (Motors will run opposite direction)
2. Phase shift between primary and secondary will be reversed. So if you have a standard ANSI transformer, where the low side lags the high by 30 deg, swapping inputs to H1 and H3 will result in low side leading the high side by 30 deg.
The phasor diagram on the nameplate is based on a normal positive phase sequence being connected to H1-H2-H3. If you reverse the input, the phase shift will be in the opposite direction from what is shown on the nameplate.
So if you attempted to parallel this transformer with another transformer connected differently, things would be very exciting for a few cycles.
There may have been a phase sequence relay that tripped when H1 and H3 were swapped.
I ad a transformer with a rising level of combustible gases. We pulled it and sent it ou for rework. When it came back, we did the standard battery of tests, including turns ratio test.
Running the turns ratio test, we found things NOT working right. Investigation revealed that the nameplate showed X0-X1-X2-X3, and that's the way the hard bus on the secondary was connected. However, the rebuild came back with x1-x2-x3-x0. The transformer went back on the truck and back to the service center for a fix.
