the magnetising current
the magnetising current
(OP)
The magnetising current inrush in a transformer is rich in 3rd harmonic?
yes or no?
yes or no?
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the magnetising current
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the magnetising currentthe magnetising current(OP)
The magnetising current inrush in a transformer is rich in 3rd harmonic?
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RE: the magnetising current
NO
2. The magnetising current inrush in a transformer is "rich" in 2nd harmonic? yes or no?
YES
RE: the magnetising current
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: the magnetising current
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: the magnetising current
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(2B)+(2B)' ?
RE: the magnetising current
Results are attached. 3rd harmonic is 22% of fundamental.
Harmonic/Mag / Fraction of fundamental
1 34.10 1.000
2 10.81 0.317
3 7.42 0.217
4 1.10 0.032
5 0.23 0.007
6 0.70 0.021
I had a problem uploading spreadsheet, but did show a screenshot attached. Will keep trying to upload spreadsheet.
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(2B)+(2B)' ?
RE: the magnetising current
Harmonic/Mag / Fraction of fundamental1 68.13 1.000
2 19.98 0.293
3 3.87 0.057
4 2.89 0.042
5 1.90 0.028
6 0.65 0.010
This time spreadsheet updated successfully (I made it smaller)
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(2B)+(2B)' ?
RE: the magnetising current
Will 21.7% or 22% be considered "Rich".
A comment Pete;
I like to see trends rather than a single example. When dealing with non-linear issues, a single example may be misleading, unintentionally of course.
Can you easily plug in lower voltage levels (minus 10%, minus 20%)?
It will be interesting to see if the ratios of harmonics stay about the same and if different, how much and in what direction.
I suspect that a lower voltage may result in less saturation and lower harmonics, but how much less (and I may be wrong).
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: the magnetising current
If you want to look at other scenarios, that is one advantage of a simulation over a measurement... you can vary parameters in attached spreadsheet to see effect. Voltage is one... Phase angle of closing is another.... Magnetic parameters is another. (Of course measurements have other advantages and measurements /simulations compliment each other imo). You are welcome to try it if you like... see instructions tab... don't' forget the F9.
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(2B)+(2B)' ?
RE: the magnetising current
RE: the magnetising current
Very cool - thanks for sharing.
David Castor
www.cvoes.com
RE: the magnetising current
Some references below imply regarding the presence of 3rd harmonic in the inrush current :
I focused on 3rd harmoinc above because that was the question. And as we all know 2nd is more useful for discrimination of inrush.
Also I'd like to apologize to Bill / waross.... rereading my reply above sounds like some kind of over-reaction. Your very point is the one that I repeated in this post.
Also that post of mine seemed to imply that it would be valuable for someone to run my simulation with various values to study it... which is just plain silly because that model is very crude to begin with (no 3-phase attributes, no residual magnetism, etc etc). If the word "model" implies something fancy, that's not what that spreadsheet is.
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(2B)+(2B)' ?
RE: the magnetising current
What I am wondering: How to phrase this?
I understand that inrush may be mitigated somewhat by first energizing at a lower voltage and then stepping up to working voltage.
With that understanding, I wonder if the ratio of the harmonics would be the same in a transformer energized at 80% or 90% of normal voltage as the ratio when energized at full voltage.
This information may then transfer to transformers designed to work at different flux densities.
I understand that 2nd harmonics result from saturation and odd harmonics result from a distorted waveform. These effects are related but may not be exactly the same.
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: the magnetising current
H 100% 90% 80% 70% 60
1 1.00 1.00 1.00 1.00 1.00
2 0.29 0.32 0.36 0.41 0.47
3 0.06 0.04 0.02 0.02 0.09
4 0.04 0.05 0.07 0.07 0.06
5 0.03 0.02 0.01 0.01 0.05
6 0.01 0.02 0.03 0.03 0.01
For this particular model, there is a clear pattern that as we increase voltage, the 3rd harmonic goes up and the 2nd harmonic goes down. What is the conclusion, I'm not sure, but I'm open to comments what insight this gives and how it might relate to real transformers.
fwiw, in slide 8, I included Fourier analysis of a what would be current output of a halfwave rectifier feeding a resistive load (sin pulse for half cycle, zero for other half of cycle).
1.00 1.00
2.00 0.25
3.00 0.11
4.00 0.06
5.00 0.04
6.0 0.03
It is of course not a realistic recreation of a transformer inrush, but it is the simplest waveform that resembles the transformer inrush and has the advantage that you could calcualte it by algebra (instead of numerically). But I was too lazy to do that.
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(2B)+(2B)' ?
RE: the magnetising current
H 110% 100% 90% 80% 70% 60% 50%
1 1.00 1.00 1.00 1.00 1.00 1.00 1.00
2 0.27 0.29 0.32 0.36 0.41 0.47 0.53
3 0.07 0.06 0.04 0.02 0.02 0.09 0.21
4 0.03 0.04 0.05 0.07 0.07 0.06 0.01
5 0.03 0.03 0.02 0.01 0.01 0.05 0.05
6 0.00 0.01 0.02 0.03 0.03 0.01 0.04
Does it mean anything to you Bill? I'm not sure what to make of it.
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(2B)+(2B)' ?
RE: the magnetising current
My apologies for excess number of posts.
I'm done now.
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(2B)+(2B)' ?
RE: the magnetising current
The numbers seem to be going in the opposite direction to what I expected. Now I'm going to spend a few days digesting this.
Thanks again.
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: the magnetising current
RE: the magnetising current
1 1.00
2 0.42
3 0.00
4 0.08
5 0.00
6 0.04
I double checked the other reported frequency components and they are correct.
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(2B)+(2B)' ?
RE: the magnetising current
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: the magnetising current
RE: the magnetising current
I'm running up a new dry cast transformer tomorrow. No load on it yet but it will feed some 11kV pumps in the coming weeks. I'm connecitng a Ranger 7000T power quality analyser to get a feel for it's effect on the system, including harmonics. I'll post the results tomorrow evening (GMT) just for interest.
RE: the magnetising current
I can't agree with your opinion. My very first answer was absolutely serious.
Question was "yes or no?" and my answer was "no". In addition I stated the similar question referring to the 3-rd harmonic and I answered "yes".
By and large Pete's data confirmed it.
Regards
CL
RE: the magnetising current
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: the magnetising current
I found that in my text above the last-but-one sentence should be correctly in such a way: "In addition I stated the similar question referring to the 2-nd harmonic and I answered "yes".
A mistake may be a fatigue symptom.
Regards
CL