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Detailed Losses for multiple transformers


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Hello Fellow PVsyst Modelers!

I have a (hopefully) quick question regarding using the default values for multiple transformers in a system.

For example, I have the following system:

Module Strings > DC Combiner > Inverter > Unit Transformer > GSU Transformer (at substation) > (Meter) > Transmission grid tie-in.

My colleagues and I have determined how to use the Ohmic losses Detailed Computation to obtain loss fractions at STC for each of those stages separately, which we then add together outside of PVsyst and put the sum of the losses in the DC or in AC as applicable.

On the external transformer, there are two in the system: the Unit transformer, and the GSU transformer.

Assuming that we have the constant loss and inductive losses at STC for both, can we enter the sum of these losses for both the unit transformer and the GSU in the corresponding fields in the "External Transformer" section?

Extending that, in case we do not have such detailed information, can we use double the default values?

Is this approach accurate?

Thank you,


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  • 2 weeks later...

In the present time, PVsyst only allows to define a simple output circuit, with one transformer.

The loss is expressed in terms of percentage of the Peff (corresponding to STC) value.

Now if you have several transformers, the easiest way id to simply add the ohmic loss (in terms of percentage) of the first and the second transformer.

Working explicitly on the resistance of the transmission lines is also possible, but more complex. You should define an "equivalent" resistance (as "seen" from the output of the inverters) of the circuits before the first transformet, between both transformers and up to the injection point, taking the voltage ratios into account.

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  • 6 months later...

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