How to simulate a plant with several medium voltage power stations regarding the AC ohmic loss from MV transformer to injection point

[Katinka89]

Hello,

we are planning some MW plants with central inverters, more precisely medium voltage power stations combining inverter and medium voltage transformer.

Now we want to calculate the MV line losses and we are not sure how to specify.

In one project, we have four MVPS connected in series and then connected to the feeding point. We know the distances between the MVPSs and the distance to the feed point.

How can we calculate the loss correctly? Should we use four transformers and the average length to the feed point?

Or one transformer? Then what length do we need to insert?

I hope that the question is understandable ...

Thank you!

[Muhammed Sarikaya]

Dear Katinka,

I don't understand how you can connect MVPS in series?

In your case, I need to know if all your MVPS have the same length to injection point?

Regards,

Muhammed Sarikaya

[Katinka89]

Dear Muhammed,

sorry, that was confusing. I didn't mean series connection in the electrical sense. But the four MVPS are connected in such a way that the segments between them carry different power. The first carries 1/4 of the total power, the second half, the third 3/4, and the last the total power.

We want to calculate the total losses of the mv line, both for the mv lines between the transformers and for the mv line between the last MVPS and the feed point.

Here are the lengths:

MVPS1-MVPS2: 0.431 km

MVPS2-MVPS3: 0.192 km

MVPS3-MVPS4: 0.369 km

MVPS4 - injection point: 7.84 km

Best regards

 

 

[dtarin]

You can use software or do it manually. You know the conductor size, length, max current carried, etc. in each segment. Calculate the loss for each segment. Then you can combine into a total loss, or keep separate. Each segment should be treated separately. If the loop is from MVPS 1 to 2 to 3 to 4, the current along the way will increase. 

[Katinka89]

Dear dtarin,

thank you very much for your quick reply.

I already know this procedure. I then enter the weighted average of the losses and only one transformer and add all the no-load and full-load losses of the transformers. Is this correct?

I just wonder if it is also possible to calculate the weighted average of the lengths to run the simulation?

Because in PVSyst, under detailed losses, you have the option to enter either the length of the wire or the loss fraction.

 

[Muhammed Sarikaya]

Dear Katinka89,

Currently, we can't design your system in PVsyst in detailed. 

I suggest you to define your system by using one big length, for example take 7,84km in the account.

You can also do a calculation to obtain the voltage drop for each portion of the distances you mentioned and then put as a global Loss fraction at STC. I think if your cables have a reasonable section, after simulation, you will not have a big difference.

If you have any other question, don't hesitate to write us.

 

Regards,

Muhammed Sarikaya

[dtarin]

13 hours ago, Katinka89 said:

Dear dtarin,

thank you very much for your quick reply.

I already know this procedure. I then enter the weighted average of the losses and only one transformer and add all the no-load and full-load losses of the transformers. Is this correct?

I just wonder if it is also possible to calculate the weighted average of the lengths to run the simulation?

Because in PVSyst, under detailed losses, you have the option to enter either the length of the wire or the loss fraction.

 

Determine the total, weighted loss fraction and use that. PVsyst will auto-calculate length based on the wire size. Let it do that, as long as the loss % is correct, and you end up with a representative value in the waterfall. 

[Katinka89]

Hello again,

thank you very much for your answers!

I have now done the following:

For each cable segment I calculated the loss fraction:

MVPS1-MVPS2: 0.07%.

MVPS2-MVPS3: 0.06%.

MVPS3-MVPS4: 0,09%.

MVPS4 - feeding point: 1,48%.

So the total loss fraction is 1.7%.

I add this value to the detailed losses and assume that I have a transformer with a percentage value for the iron loss: 0.1% and for the
copper losses: 1.0%.

Is this correct?

Thanks you