Transformers. How many?

[souparvo]

Hi,

I have a question regarding the modeling of the transformers on PVsyst. The transformer losses seem to be only accounted once, I assume the model only considers one transformer for the whole PV system. I have several designs with multiple transformers, each one on the output of each inverter. So my question is when adding the transformer losses (for the case of multiple transformers) I will have to multiply and/or sum the losses from all the transformers in order for the simulation to account for all the transformers consuming power, correct?

In my understanding the model considers one transformer for the whole system at the PCC.

Thank you!

[André Mermoud]

Yes PVsyst considers one only transformer.

If you have several ones, you should adapt the loss parameters accordingly, i.e.:

- The "iron loss" is expressed either in percentage of Pnom or in Power.

In the first case you should put a weighted average of the Iron losses of each transformer, in the second you should add the power losses.

- The "ohmic loss" is expressed in percentage of the PNom at STC. You should put a weighted average of your diffent loss factors.

Expressed in terms of resistance, this will correspond to a parallel wiring of all parasitic resistances.

Expressed in terms of energy loss, it will be the sum of course.

[Javier Perez]

Dear André,

In a standard design of a utility scale solar farm we will have one LV/MV transformer every two or three inverters and a global MV/HV power transformer. So in order to simulate all theses transformers I must add the no load losses and the load losses. The doubt is where is defined the value of PNom at STC. I suppose it is the value stated in the AC circuit STC: AC, marked in red in the attached file.

Is this hypothesis correct.

Best regards,