Modelling of each component in power system simulation correctly is the essence. Here you can find some specific guidelines on how to model a Three winding Transformer correctly in an RMS based software from Transformer Test report.

1. THREE (3) WINDING TRANSFORMER CORRECT MODELLING
IN PSS/E
August 2020 1
Transformers modelling (RMS based simulation)
 For Load flow consider the Positive Tolerance on impedance – Do not neglect as this will cost in
case of a Solar PV plant in the range of >50 MW due to quite high number of Inverter Transformers.
 For Short Circuit consider the Negative Tolerance on impedance – Do not neglect as this will
impact the short circuit level specially in PV plant RMU and LV level.
 Match the Transformer Active Power loss from Transformer Test reports and not from data sheet
– It impacts !!!!!
 Generally everybody does not focus on Transformer Reactive Power loss matching – This has
huge implication for a Solar PV plant !!!!!
 Do not forget to Verify the Transformer Regulation as per test report or Data sheet. Usually
nobody checks this one through simulation. This is one of the best check points in a simulation
software.

2. THREE (3) WINDING TRANSFORMER CORRECT MODELLING
IN PSS/E
August 2020 2
Transformers modelling (RMS based simulation)
 Correct modelling of Vector group is essential. However, mostly Zero sequence model gets
neglected by many users and this may cost in Harmonic and other phenomenon involving the SLG
fault level !!!!!
 Did we verify this ? If not, start verifying this one through simulation.

3. THREE (3) WINDING TRANSFORMER CORRECT MODELLING
IN PSS/E
August 2020 3
Transformers modelling (RMS based simulation)
 Challenge for everybody
- Prove that above formula is not correct for every 3 winding Transformer. You can do it. Google it and
its very easy.

4. August 2020 4
THANK YOU