Warning 120 | [PSS®E] | Two-winding transformer with both taps off-nominal
Relevant software:
Emitted message:
Both tap ratios for a two-winding transformer are off-nominal.
Description:
This warning indicates that both tap ratios (RATIO and RATIO2) for a two-winding transformer in your PSS®E model are off-nominal (not equal to 1.0). This configuration is abnormal and may cause benchmark issues with other software packages.
It is possible for a transformer to be off-nominal tap on both windings. For example, a transfomer which has an on-load tap changer on one winding and its second winding is on a different voltage base than the base voltage of the bus it is connected to.
However, typically, this is a sign of a potential modelling issue in your power systems model which may impact benchmarking with other software packages.
Possible impact:
- Benchmarking issues caused by unexpected ratios between the primary and secondary sides of the transformer (which might not be present in other software packages).
Potential fixes:
To resolve this warning, consider one of the following approaches:
If the current configuration is intentional and necessary for your specific modelling requirements, you can safely ignore this warning, but be aware of potential benchmarking issues with other software packages.
If the current configuration is not intentional, you can modify your transformer model to have only one off-nominal tap ratio as follows:
- Determine which winding should have the tap changer
- Set the other winding's tap ratio to exactly 1.0
- Adjust the tap ratio of the first winding to achieve the desired overall transformation ratio