Transformer at no load

[DanielFuente]

Hi everyone, I am trying to simulate the current in a transformer when it is at no load, using the software Powerfactory.

I get the Magnetization current, and it is what I was expecting.
But I get confused when I draw the phase current, because as the trafo is at no load... should not be the same the magnetization current and the phase current?

How is possible that the phase current is smaller than the magnetization current?
I don´t understand that.

The picture is the simulation of the normal operation with no load.

The thing is that I don´t understand what exactly is the difference between the magnetization current and the phase current.

 

[DanielFuente]

Here is the simulation with the magnetiztion current and phase current.

Thanks everyone...

 

[juleselec]

This is something that's a bit misleading in the software. The magnetizing current is the current that is calculated using the polynomial saturation characteristic based on the magnetizing flux. This is used to determine the magnetizing reactance, which is then used to calculate the phase current (along with the leakage impedance).

 

[7anoter4]

It seems to me you neglected primary winding impedance Zp=Rp+jXp.
Rp=primary winding wire resistance Xp=primary winding magnetic field leakage reactance.
Since Io=V/(Zp+Zexc) and Iexc=V/Zexc then Io<Iexc
Zexc=1/(1/Rfe+1/jXm)= Rfe*Xm^2/(Rfe^2+Xm^2)+jRfe^2*Xm/(Rfe^2+Xm^2)=Rexc+jXexc

 

[7anoter4]

Sorry,wrong sketch!

 

[jghrist]

The software is using two different models of non-linear flux. It is using a simplified linear model to calculate phase current and a more realistic model to calculate magnetizing current. In the normal case of a loaded transformer, the simplification for the phase current would not result in a significant error. Of course, for an unloaded transformer, the phase current and the magnetizing current are identical (if capacitance is neglected).

 

[DanielFuente]

Thanks a lot for your answers, they really help.

But I don´t understand your explanation 7anoter4 about that Io<Iexc

I mean that

Io=V/(Zp+Zexc) and Iexc=(V-VZp)/Zexc


and so there is no option for I0 being smaller than Iexct.

--------
Other thing that I would like to comment is the difference between
the phase current of the line at the begining and at the end of it.
I add the image.

How can they have such a difference shape and value?

Have you got PowerFactory?
If you want I could send you the file.dz


Thanks a lot.

 

[7anoter4]

These are not measured currents, I think, but simulated[calculated]. If you calculate Io taken into consideration the transformer winding resistance and magnetic flux leakage reactance[Zp] in series with Rfe|| Xm you will get less current compared with the case in which you neglect the Zp[obviously, is not it?].In your o.p. sketch Zp is missing [it seems to me].
Actually Io is equal with Iexc if you take into consideration both currents[Ife+jIm]

 

[7anoter4]

Employing the Flux to Current usual curve we get the magnetic current curve as showing[the green lines]. The red curves have to be if we will take into consideration "two slopes" diagram. It seems to me a third harmonic is involved. This phenomenon occurs in YN transformer connection.
However, usually, iron core saturation will produce triplen harmonics.

 

[DanielFuente]

Really useful 7anoter4.
I ll think about it.

Thanks a lot