Powerfactory zero sequence voltage calculation

[Electrical1948]

Hi all,

I was refreshing my symmetrical components theory and performed a calculation in Power factory (Digsilent) to compare against my calculations in Excel. I got all of the figures correct, however I am unable to calculate a zero sequence voltage component "through" a transformer.

The input data are as follows:
Operating voltage (Grid): UAN = 230 V <0 deg, UBN = 235 V < -120 deg, UCN = 240 V <120 deg

Transformer:
Rated voltage HV winding: 400V
Rated voltage LV winding: 400 V
Vector group: Dy11

I calculate the following symmetrical components on the HV side:
U+ = 235 <0 deg
U- = 2.887 < -150 deg
U0 = 2.887 < 150 deg

I calculate the following symmetrical components on the LV side:
U+ = 235 <30 deg
U- = 2.887 < 180 deg

I can't calculate U0 since I do not have the phase to neutral voltages. However, Powerfactory calculates U0 = 1.443 < 60 deg, which I do not understand.

Is there anyone who can explain how the U0 is calculated by Powerfactory?

 

[7anoter4]

If we recalculate the Delta phase-to-phase voltages using voltages phase-to-neutral the absolute value is not 400 V but 402.7 AB, 411.4 BC and 407 CA. That means the phase-to-neutral voltages are different.
If Powerfactory software may approximate these different phasor values in order to reach a symmetrical 400 V Delta may be the Uo could be different.
I did myself an approximation changing only absolute value of the phase-to-neutral phasors and I got Uo=1.45 <150o.

 

[Electrical1948]

Hi

Thanks for the reply.

Can you show how you did the approximation to get U0=1.45?

 

[7anoter4]

First, I calculated the primary phase-to-phase angle and I took for secondary phase-to-neutral the same angle[see the sketch].
Then I calculated the secondary phase-to-phase voltage using these phase-to-neutral secondary voltages, changing the absolute value -only-in order to create a symmetrical 400 V secondary system.
However, since I did not save the calculation, and I did not remember
the changed absolute values I did another turn of changes, but it still not as the latter.
Now I got Uosecondary=1.709<54.6o only.