Modelling transformers with asymmetric charged susceptance

[eperim]

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Issue

Pandapower offers two approaches to modelling transformers: one is to use a symmetric pi-model, with equal susceptance values on each terminal; the other is to use a t-model, with the susceptance in the centre. Looking at the source code, it seems that both models ultimately get translated into a symmetric pi-model.

However, it is not uncommon for asymmetric models to be employed, particularly one in which the charged susceptance is applied only on the tap side. Is there any way to simulate this kind of model within Pandapower? Or does it fundamentally require using symmetric transformer models?

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[vogt31337]

@pawellytaev what is your opinion on this?

@eperim I am not sure I think there are already some efforts on this regard. What exactly is your use case?

[eperim]

@vogt31337 I am collaborating with people that use proprietary software which models transformers with the shunt only on the tap side, and that is introducing some significant discrepancies on the power flows I get using pandapower. Ideally, if I could specify two susceptance values, one on the HV side and another on the LV side, I'd be able to reproduce their results.

[vogt31337]

Hmm I think there IS some development in that direction. Maybe you can "emulate" that behaviour by adding additional impedances / lines behind the Transformer, I think there are "easy" workarounds...
Maybe @pawellytaev knows more.

[pawellytaev]

Hey @eperim , currently pandapower doesn't support asymmetric admittances for trafos. However, we are planning to have this as a feature in the future, but haven't started it yet. In the current develop branch we have already added the G_ASYM and B_ASYM as additional columns to the ppc['branch'] table which gives us the possibility to have this feature.

We have added asymmetric admittances to the impedance element https://pandapower.readthedocs.io/en/latest/elements/impedance.html#pandapower.create_impedance (new parameters gf_pu, gt_pu, bf_pu, bt_pu) where you have asymmetric admittances. So you can try and emulate your case with this one (only works for trafos with phase shift = 0, since impedance elements don't have a phase shift in pandapower)

[pawellytaev]

Do you see asymmetric admittances relevant both for 2w and 3w-trafos? I have personally only seen this in other software in their 3w-trafo model

[eperim]

@pawellytaev Thanks for the info. Unfortunately, I'm also dealing with transformers that are phase shifters. Think I'm out of luck =/

In the case I am dealing with, the admittance is asymmetric for both the 2w and the 3w transformers. I wouldn't know how common this is, though.

[pawellytaev]

Hm, do you know the use case of trafos with asymmetric admittances? I can't think of a specific reason why one would model them this way in a pi equivalent circuit.

[eperim]

I don't, but I am not a power systems (or electrical) engineer, so I am not really the best person to answer that. In the specific case I am dealing with, it's not just asymmetric, but it has no added shunt at all on the side opposite to the tap (not sure if that makes it more reasonable than modelling it with just a general asymmetric model or not, when it comes to the physics of the component).