4th Harmonic Created by Transformer
4th Harmonic Created by Transformer
(OP)
We have had an issue on site where there was a intermittent 4th harmonic, today we finally managed to recreate the problem by energizing a large transformer.
Could anyone explain why / how this transformer is creating these?? I was always under the impressions that harmonics were usually created by power electronics.
Thanks
Could anyone explain why / how this transformer is creating these?? I was always under the impressions that harmonics were usually created by power electronics.
Thanks





RE: 4th Harmonic Created by Transformer
Iron is symmetric and shouldn't produce even harmonics. Third, fifth etcetera are common if core is run close to saturation. But never even harmonica. That either needs DC injection or a core that has been in hard saturation and remains so - high remanence.
Gunnar Englund
www.gke.org
RE: 4th Harmonic Created by Transformer
RE: 4th Harmonic Created by Transformer
I think of intermittents as somthing that comes and goes during normal operation and after all switching transients have died out.
Gunnar Englund
www.gke.org
RE: 4th Harmonic Created by Transformer
RE: 4th Harmonic Created by Transformer
But, I once had a semantic discussion about that. The fundamental is not a harmonic. So the 100 (or 120*) Hz should be called the first harmonic. And the 150/180 Hz should be called the second harmonic. That leaves us with the possibility that the OP actually means 250/300 Hz (what we usually call the fifth harmonic).
So, another question would be: What frequency are you seeing?
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* Depending on the mains frequency, 50 or 60 Hz.
Gunnar Englund
www.gke.org
RE: 4th Harmonic Created by Transformer
I've always assumed that the harmonic order is the ratio of fundamental to harmonic frequency, i.e. 150Hz / 50Hz = 3, ergo 150Hz is the third harmonic of 50Hz.
I suspect you are trying to cause anarchy!
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I don't suffer from insanity. I enjoy it...
RE: 4th Harmonic Created by Transformer
We looked at our UR relays, they are showing 4th harmonics, that's about it, came as a little bit of a surprise to myself as well but being fairly new to the field and only really having school as my background figured I would pop the question.
And these harmonics don't hang around very long, basically right after the energizing of the transformer and that's it, the system runs like a charm otherwise.
RE: 4th Harmonic Created by Transformer
Was referring to 240hz on a 60hz system and when we throw the switch it is powering up 2 500KVA xfmrs
RE: 4th Harmonic Created by Transformer
Yes Scotty. But I hope you agree that the first harmonic is partial tone number two? I have had this discussion with a junior that actually got me wrong when I was saying someting about third harmonics adding up in the neutral. He couldn't believe me. Third harmonics were 200 Hz to him.
Gunnar Englund
www.gke.org
RE: 4th Harmonic Created by Transformer
Gunnar Englund
www.gke.org
RE: 4th Harmonic Created by Transformer
They have a solution to our problem, take the filter bank off line while energizing the transformers, their thought behind this is the filter bank is set to remove any 5th harmonics but while doing this is amplifying the 4th during energizing. My guess is that the inrush current is making the filter bank resonate at the 4th.
And that's my guess, it seems to be working, if anyone can add that would be great.
Thanks
RE: 4th Harmonic Created by Transformer
5th harmonics - Overexcitation condition in transformers.
Even harmonics are a clear indication of an inrush condition - as you noted especially during energizing of the transformer. What are the percentage 2nd and 4th harmonics? What kind of filter bank do you have? The resonant condition sounds like a reasonable guess. Maybe a little off-track, but have a look at this paper:
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RE: 4th Harmonic Created by Transformer
Gunnar Englund
www.gke.org
RE: 4th Harmonic Created by Transformer
Just out of curiosity, why is this being considered a problem? From my understanding this is typical behavior for a transformer being switched on. If so, do you really need to address a transient event such as that?
The reason for my asking is somewhat selfish in that I have raised this question (through a PE friend) to someone on the IEEE 519 committee with relation to motor starting and have yet to receive an answer. My point was that if it is a transient event that is part of a normal operating condition, does it need to be included in a harmonics study at all? What I was told is that IEEE-519 does not technically include language pertaining to the time factor of a distortion. The shift to requiring a TDD study instead of a THD study will solve that issue anyway however, because a startup transient, be it a motor or transformer, is such a miniscule percentage of the total demand that it becomes insignificant. I'd love to hear other's thoughts on this, but if everyone thinks this is too OT to the original question, RF it and I'll start a new thread.
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