Quick Question for westie - phase shift

[Adam_151]

Is it possible for the phase angles in a three phase supply to be wrong?. A logging instrument is reporting that the angles between the current waveforms (it does not seem to provide those for the voltage waveforms - or at least I've not worked out what key to press yet) are R-Y 120 ish degrees, Y-B = 165 Degrees, b-R = 75 degrees.

Something in the back of my mind suggests that reverse polarity on a primary winding shifts by 30 Degrees? and the figures are probably a little off what you'd expect because these are the current waveforms and the PF isn't that great

If this is so, what P-P voltages would one expect to see, I didn't think to measure them at the time, but will be back there

Many thanks

 

[JohnW2]

A logging instrument is reporting that the angles between the current waveforms (it does not seem to provide those for the voltage waveforms - or at least I've not worked out what key to press yet) are R-Y 120 ish degrees, Y-B = 165 Degrees, b-R = 75 degrees.

Is it not possible, at least theoretically, to get current waveforms like that simply because one or two of the phases has a highly reactive load (i.e. poor PF), even if the voltage waveforms are all 120° apart? However, I assume that you would have mentioned if there were any such loads involved. Also, is this (to your knowledge) a new situation - i.e do you know that it's been different (and more 'as expected') in the past?

Kind Regards, John

 

[endecotp]

Is it not possible, at least theoretically, to get current waveforms like that simply because one or two of the phases has a highly reactive load

Yes. And consider what will happen if there is (almost) no load: you'll see a small current that lags the voltage by 90 degrees due to the parasitic capacitance of the wiring.

If there is almost no load, I'd expect these current phase angle measurements to be rather bogus - like measuring the AC voltage on an open-circuit wire.

Question: What load is connected in this case?

 

[bernardgreen]

Those figures suggest the current in the blue is out of phase with its voltage. ( It is highly unlikely the incoming blue voltage is 45 degrees out )

So look for heavy reactive loads on that phase. ( or a fault in the logging system, swap the blue sensor with the red sensor and see if the "error" changes )

 

[westie101]

Never come across it