Clarification on Average Wire Length in MV Line (Transformer to Injection Point)

[Niken13]

Dear PVsyst Team,

I have been reviewing the AC wiring losses in the system, specifically the data provided in the report for the Inverter output line up to the MV transformer and the MV line up to the injection point at 20 kV.

Upon reviewing the report, I noticed a potential misunderstanding regarding the interpretation of the "average wire length" in the MV line section.

In the report, it mentions:

• Average wire length for the MV line up to the injection point as 760 meters.

However, the way the data is presented could lead to confusion. Initially, it seems that this distance refers to the wiring between the inverters and the MV transformer. But upon further consideration, it seems that the 760 meters should be the distance from the MV transformer to the injection point (where the power is fed into the grid at 20 kV), not per inverter.

To clarify:

• The average wire length should indeed be for the MV line from the transformer to the injection point at 20 kV, and not per individual inverter.

• The inverter-to-MV transformer wiring and the MV line from the transformer to the injection point are distinct, and it's important to apply the loss fraction of 0.25% to the wiring between the MV transformer and the injection point, where the power is being injected into the grid.

Could you please confirm whether this interpretation aligns with how the data is calculated in PVsyst? And, if possible, could you confirm the accuracy of the wiring loss fraction applied to this MV section?

Please have a look to the attached screenshot of the PVsyst report.

Looking forward to your insights and confirmation.

Best regards,
NIken

[André Mermoud]

Yes, this is an error in the report. This represents indeed the loss at the output MV line of the Transformer. We will correct this for the next version.

When defining the wiring losses in PVsyst,  the frame "Array wire loss inverter to transfo" concerns the connexions from the inverter to the transformers, and  "Medium Voltage Line" the output of one transformer.

The evaluation of the wiring loss is indeed a direct calculation of the loss, at each hour, according to the specified wire resistance and the instantaneous current. There is no uncertainty here, as far as the resistance is well defined. When specified as a percentage at a given power, the resistance is directly calculated from this loss (no error).

The only uncertainty could be the resistivity variation according to the wire temperature: in PVsyst this is defined for 50°C, the variability being 0.39 %/°C.