Transformer Inrush Question from an ME
Transformer Inrush Question from an ME
(OP)
Hello,
I've read through several articles on transformer inrush, but I'd like to poke around the great EE minds here to see if I can get a physical explanation of why transformer inrush is only one direction (or polarity), (see the example waveform we captured in the link).
Much appreciated
I've read through several articles on transformer inrush, but I'd like to poke around the great EE minds here to see if I can get a physical explanation of why transformer inrush is only one direction (or polarity), (see the example waveform we captured in the link).
Much appreciated






RE: Transformer Inrush Question from an ME
RE: Transformer Inrush Question from an ME
So the offset is not always in one directon and sometimes does not even occur. In a three-phase transformer, each phase will exhibit a different waveform since the three voltage phase angle will be different.
RE: Transformer Inrush Question from an ME
RE: Transformer Inrush Question from an ME
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Transformer Inrush Question from an ME
I know electricity is especially hard to describe physically, but can you guys give a good physical explanation? Does it have anything to do with response time of the current/flux (like the high dv/dt poking the flux in the rear with a hot iron telling it to get a move on)? My big question is that my waveform doesn't look like the dc offset stuff we saw in electronics 101 where the entire waveform shifts up or down. It looks like the positive peaks are amplified and the negatives aren't affected, so if this is DC offset during transformer inrush, how is this happening?
RE: Transformer Inrush Question from an ME
On inrush the current into unmagnitized wire that is the transformer, will reduce the voltage, which unbalances the equil trading of energy from inductive to capacitive, leaving a deficet which is fed into the new part of the circuit. The amount of inrush will depend on where in the power cycle you are at the closing of the switch. If you are near a zero energy stored point, you should experence zero Dc offset. The inrush will however still take place, just not the offset.
If there are any corrections, or additions, please make them. As I am not a teacher, I may not have said something correctly.
RE: Transformer Inrush Question from an ME
RE: Transformer Inrush Question from an ME
RE: Transformer Inrush Question from an ME
current transformer?
Just some more data that may help understand....resistor in series with lead?
is it one phase of a 3 ph transformer?
primary or secondary?
can you include a voltage too on channel 2 of scope?
was scope on AC or DC input coupling?
what happened before the steady state 100App on left?
can you get pix starting with 0 amps?
RE: Transformer Inrush Question from an ME
http://www.electrical-installation.org/enwiki/Tran...
https://www.google.com/search?q=transformer+inrush...
http://relays.te.com/appnotes/app_pdfs/13c3206.pdf
RE: Transformer Inrush Question from an ME
RE: Transformer Inrush Question from an ME
RE: Transformer Inrush Question from an ME
RE: Transformer Inrush Question from an ME
It was taken at the building main, and the disconnect switch is fed through a main switchboard and it's branch circuit breaker.
I can't answer on the AC or DC input coupling, the analyzer is a blackbox, and unfortunately it only captured triggered events so I don't have any cycles before or after these.
RE: Transformer Inrush Question from an ME
Does the reason for the inverse peaks of the current not being affected much have to due with the back emf returning and creating more normal impedance?
RE: Transformer Inrush Question from an ME
There is also a residual flux in one direction depending on the point on the voltage wave where the transformer was deenergized. This residual flux will add to the current if the flux is in that direction when it is reenergized.
RE: Transformer Inrush Question from an ME
That would be due to saturation of the transformer core by the instantaneous value of the inrush current. Since this value is equal to the sum of the sinusoidal and the DC offset (the exponentially decaying component), it is higher (absolute value) on one side of the waveform than on the other. So the shape of the waveform is affected asymmetrically.
Its sort of a 'back emf' issue in that the magnetizing current creates a core flux which in turn produces this back emf. But once the core reaches saturation on each peak, very little additional flux and back emf is produced, resulting in that sharper spike on the top of the waveform.