hv trafo loss AC losses in transformers

[Kanagavel K]

Dear PVsyst Team,

I need some clarification on the AC Losses portion,

1) AC Transformer Losses portion While defining the losses from the datasheet tab (6600kVA Nom.Power) 3 Nos of Trafo is used in the project so total Nom.Power will be 19800kVA. here, the point to be noted is that no value of temperature is being defined in PVsyst. 

Then, how the Nominal power at STC calculation is performed in internal pvsyst (at transformer side).

2)  AC Wire Loss Inverter to Transfo  Inverter ratting Nominal power at 50deg is 275kVA and as per the power vs temp curve (image is attached here for the reference) 20 deg to 30deg the power is 330kVA only

Then, how the Nominal power at STC calculation is performed in internal pvsyst (at inverter side).

 

 

 

[André Mermoud]

In the AC losses part, the reference power may be either the STC power of the PV array, or the PNomac output of the inveters. This choice is done in the project's settings:

In this case the PNomac of the inverters is the nominal power (not the possible max. power at low temperature). 

NB: In your case the choice of the reference power is the array STC power (nameplate of the PV modules). 

However the reference power choice affects the ohmic loss parameter when expressed in terms of percentage. The basic definition of the ohmic losses is the cable Resistance. When operating, the ohmic loss is proportional to the square of the current. When expressed as percentage of the power it is proportional to the power. 

This is explained in detail the help https://www.pvsyst.com/help/project-design/array-and-system-losses/ohmic-losses/index.html.

As an example: 

You have defined a MV lines loss of 1% for a  PNom at STC = 8.2 MWp  (PV array). 

Now if you have a PNomac(inv) of, say, 6 MW, the relative loss at PNom(inv)  will be 1% * 6MW/8.2MW = 0.73%. 

You can check that if you change the referenc power in the project's settings, the relative losses will drop accodingly in this dialog.