Modelling transformers with asymmetric charged susceptance

[eperim]

Feature Checklist

• [X] Searched the issues page for similar reports

• [X] Read the relevant sections of the documentation

• [X] Browse the tutorials and tests for usefull code snippets and examples of use

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?

Label

• [ ] Relevant labels are selected

[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).

[vogt31337]

@eperim, maybe you can provide a simple example with concrete values, so that we can later on test if our implementation is working with your use case?

[eperim]

@vogt31337 I could look into sharing one of the examples I used as reference, but those are in PSSE's RAW format. Would that work for you?

[vogt31337]

@eperim, personally do Not know that Format. I would prefer to have a short Code snippet, which created such an asymmetric Transformer, does a calculation, Like PP.runpp and the checks the results If they are correct. Thanks in advance.

[omalleyconor]

Hi, would the following snippet suffice? It calculates the flow in a transformer for different phase shifts but the magnetizing inductance shunt is only applied to one side of the transformer. Calculate_Flow.zip

[pawellytaev]

Hey @omalleyconor, thanks for sharing the code snippet! Very helpful :-)

Just a few questions to check if my understanding is correct: From what I understand from your code, the trafo model would look like this

(sorry for my bad MS Paint skills)

Is there also the possibility to model the asymmetric Y_sh somewhere else? e.g. at the LV side after the Z_br, or between the ideal transformer and the Z_br?

If yes, then this has the following implications on the pandapower internal structure: TL;DR It is generally possible to implement this feature in pandapower, but the exact way how to do it has pro's and con's. We will take this up internally in the dev team and come back to you here.

Long version: Here are the possibilities I see to implement this in pandapower (for internal consideration): Either 1) We add the Y_sh as G&B to the ppc['bus'] table - Pro: easy to implement, Con: but then we have trafos modelled both in ppc['bus'] and ppc['branch']

Or 2) We add an additional branch element in ppc['branch'] with R&X=0 and G&B=Y_sh.real&Y_sh.imag and the trafo branch with R&X>0, G&B=0 - Pro: trafo only modeled in ppc['branch'], Con makes out of one trafo, 2 branch elements in ppc['branch']

We'll consider both options internally.

Cheers, Pawel

[omalleyconor]

Hi @pawellytaev ,

Thanks for the thoughtful response, I think option 1 would make most sense. It would need to add some checks that the transformer "Flow" includes the shunt but this is relatively easy to do in post processing.

Thanks