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External Transformer Losses
https://forum.pvsyst.com/viewtopic.php?f=25&t=257
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Author:  dominic.lopez [ Wed Nov 07, 2012 10:16 pm ]
Post subject:  External Transformer Losses

I am having some PVsyst hourly analysis data issues I was hoping you could lend some advice on. I am currently running into this issue for multiple projects and its affecting our financial model. The losses are coming from the transformer and when the system is off at night we are receiving the losses in PVSyst because power is still being used by the system to power monitor systems, security lights, etc. There is an option in PVsyst under 'PV field detailed losses parameter' - 'Ohmic Losses', if I leave the ‘Night Disconnect’ unchecked the losses from the transformer do not show up when i extract the hour hourly kwh data file (CSV). Would anyone suggest to leave this box unchecked, or are there any other options to mitigate this loss in PVsyst, and why? Are there any external mechanism that can shut off transformer when the system is not on, and will they still provide power to power the systems needed at night for the sight? Thank you for the help.

Author:  André Mermoud [ Mon Aug 12, 2013 2:01 pm ]
Post subject:  Re: External Transformer Losses

This loss corresponds to the iron loss of the transformer, it is proportionnal to the voltage applied to the secondary.

It occurs during the full time, when the transformer is connected to the High Voltage grid.
Now if you have a switch between the output of the inverter and the high-voltage line, which is open during night, you can check this option.
Otherwise you shouldn't of course.

Author:  mhamon [ Mon Aug 12, 2013 7:17 pm ]
Post subject:  Re: External Transformer Losses

Dominic,

You can install a switch to disconnect the transformer secondary at night. If your inverter does not have a night disconnect control then you will also need a control system to operate the switch. If you are powering site loads from the transformer you will need to install a secondary transformer to power the site.

Reasons to do this:

Reduce tare losses at night.

Reasons not to do this:

Regular reconnection of MV and HV transformers may reduce their life. Check with your transformer manufacturer.
Cost of recloser, control system, and secondary site power distribution will take a bite out of the cost savings from disconnecting the transformer. Maybe enough to make it not worthwhile.

With "Night Disconnect" unchecked you should be seeing tare losses subtracted from production, and energy being used at night. This is the opposite of what you said so you should go over that again and verify that it is working correctly. You might be looking at the inverter output and not the output at the POCC after the transformer.

Author:  cderhammer [ Wed Aug 21, 2013 8:46 pm ]
Post subject:  Re: External Transformer Losses

It sounds like these losses are strictly at the transformer. Am I correct in assuming it does not include the tare losses of any inverters in the model (which would be minor)?

Thanks!

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