How to input MV line losses when a feeder collects more than one Power Station

[jonipa]

Hello!

I am trying to understand how to enter the MV line loss percentage. Let me explain an example:

I have a circuit collecting 3 Power Stations with 1 transfo each. The calculated power losses of the MV line are:

PS1-PS2: 0,05%

PS2-PS3: 0,03%

PS3-SET: 0,07%

In total I have a power loss of 0,15% but, when entering the data into PVSyst should I enter the mean between each power station and substation (0,05%) and assume there are 3 transfos as shown below?

Thank you very much in advance!

Edited August 17, 2022 by jonipa

[jonipa]

Sorry, when writing the losses between each Power Station and substation assume they are a certain value in Watts (unknown) and that the total percentage is 0,15%.

[André Mermoud]

I don't understand well what are your power stations, and what you mean by "PS1-PS2", PS2-PS3" and "PS3-SET".

If these are  transformers in series, PVsyst only treats two stages, i.e. a  section  "Inverter => MV transfo", and a section "MVTransfo => HV transfo". The wire between HV transfo and  Injection is indeed not taken into account (this is a weakness of PVsyst). In this case the losses (in percentage) should indeed be added, as they concern the same power or energy flux.

Now when you define 3 MV transfos as you did, this means 3 circuits  "Inverter => Transfo" in parallel. In this case the losses have obviously to be added in terms of energy (kWh). And the loss in percentage will be the total loss in energy, divided by the total transferred energy.

Please carefully read the Help   "Project design > Array and system losses > AC ohmic loss from inverter to injection point"

And also  "Project design > Array and system losses > External transformer losses"

 

 

 

[dtarin]

Calculate the weighted average and enter 1 transformer. If you have the no load and full load losses for the transformer add them together when entering 1 transformer 

Edited August 18, 2022 by dtarin

[jonipa]

Thank you André, so if I understand right it would be really helpful to confirm the following:

1. What do you mean with "The wire between HV transfo and  Injection is indeed not taken into account (this is a weakness of PVsyst)" I understand if I enter the losses for the High Voltage line inputs they are taken into account right?
2. 
3. I am still not sure how to manage the losses for different MV circuits in parallel with a number of MV transfos in series each.

Taking a look to the Help you mention:

In the last line, it mentions defining an average lenght, so considering my input are the power losses, I should define an average loss for each transfo and mantain the total number of transfos of the system. Is this right?

As an example, if I have two parallel circuits with 3 transfos in series each, and the total power loss of both circuits is 0,6% I should enter and average loss of 0,1% for each transfo, right?

Thank you very much.

[dtarin]

3 minutes ago, jonipa said:

As an example, if I have two parallel circuits with 3 transfos in series each, and the total power loss of both circuits is 0,6% I should enter and average loss of 0,1% for each transfo, right?

Thank you very much.

Your total power loss is 0.106%. The first segment carries 1/3 of the total power. The second segment carries 2/3s. The final segment carries 100%. That is total loss for the entire plant. Enter that for the MV ohmic loss %.

[jonipa]

Thank you dtarin, understood. But why entering only 1 transformer with the sum of losses of all the transformers?

[dtarin]

Either is correct, you can enter 3 and average the no-load and full-load loss, or add them into one. Since you have combined the MV ohmic losses into a single loss, I suggested to do the same with the transformer, perhaps a bit more accurate instead of averaging them, since pvsyst is using the total power into the transformer 

[jonipa]

Shouldn't I enter 3 transfos anyways so that I let PVSyst know that the averaged MV line losses repeats 3 times? If I only enter 1 transfo I am afraid the total MV line power losses will only be considered 1 time. 

[dtarin]

.

Edited August 18, 2022 by dtarin

[dtarin]

The total ohmic loss is a single loss, the sum of the weighted averages. This would correspond to a single transformer loss, the sum of the transformer losses.  If you wish to use three then use the straight average. My preference would be to use the former. Run both and check the difference 

[jonipa]

Right, I'll check. Summarizing, I understand the two options as follows, seeming 2 as the more accurate one:

1. If input the total number of transfos: Average the total power losses (∆Ptotal / num transfos).
2. If input only one transfo: Input the total power losses and add up all the no-load loss, full-load loss and power in the transformer data.

[André Mermoud]

Sorry, I wrote a stupidity. I did not find the dialog for the HV line up to the grid injection, as it only appears when you choose the HV transformer in the combobox.

I was really aestonished of that, I did not remember that I had programmed this as such (a long time ago). 

[cookieezz63]

As an example, if I have two parallel circuits with 3 transfos in series each, and the total power loss of both circuits is 0,6% I should enter and average loss of 0,1% for each transfo, right?

[cookieezz63]

I should define an average loss for each transfo and mantain the total number of transfos of the system. Is this right? https://teatv.ltd/
 
https://hellodear.in
 

[dtarin]

The number of transformers doesnt really matter in PVsyst, it will create a single transformer for the transformer loss calculation. For ohmic losses, calculate the total weighted average power loss for the entire system and use that for the medium voltage line input. From your previous post, if the total power loss of both circuits is 0.60%, that is what you will enter for loss fraction at stc (assuming that value was calculated at stc conditions). Regarding your previous post , the average loss would not be 0.1% for each transformer. In each circuit, each "leg" is carrying a different current value. The first leg is 1/3, the second is 2/3, and the last leg is 3/3.