3 Phase Errors

Hi …

I’m considering purchase of an emonBase plus emonTx V3 plus the necessary bits & pieces.

My purpose is to collect daily historical data of system performance – 3 phase supply to house & outbuildings and with a large ground mounted solar PV installation.

Consumption will be difficult to monitor so a Type 2 approach …
Consumption = Generation +/- Import/Export

Question 1: Generation data will come from the Inverter and be available to the Raspberry Pi from the LAN – will it be possible to incorporate this data into emon?

Regarding Import/Export & noting that …
 Even with the 3 phase firmware upgrade to the emonTx V3, there will be CT sensor errors due phase imbalance
 The utility meter pulses picked up by the pulse sensor will stop when exporting

Question 2: Would it be possible to use meter pulses when the CT sensors on ALL 3 phases are registering IMPORT and when this is not the case, to use the CT sensor data? Alternatively, might it be possible only to use the CT sensor data but apply a correction factor periodically derived by comparing pulse & CT sensor data during periods of Import on all 3 phases?

Any comments or suggestions – most welcome – thx.

Into emoncms - running on your Pi? I believe that will be possible - provided that on the way you can format the data so that it’s acceptable to emoncms.

Strictly speaking not just CT errors but also errors due to voltage imbalance and all the other assumptions of the 3-phase sketch.

As far as we know, that’s correct. Most meters, if you’re lucky, stop emitting pulses when exporting. If you are very unlucky, they don’t distinguish between import and export and you get charged for the energy you export.

You’d need to write a quite involved piece of logic to add on to the sketch in the emonTx in order to do that.

Theoretically it should be possible to calibrate on the fly using the pulse input, but I foresee big problems with getting the algorithm right - the principal problem being you know (or think you know) accurately the current in each line and the voltage in one, but you’re guessing the voltage (hence the power and energy) of the other two lines and you only know the total energy from the meter pulses, so how do you distribute the correction across the 3 phases?

Robert …
Thank you for your super fast and super clear response.
Modifying generation data formats and Arduino sketches is beyond my skill level.
So being pragmatic/practical with a basic need for a summary monthly performance report …
Is it safe to assume that the Optical Sensor data and data from the 3 CT sensors will be found on the RPi’s SD card and the emoncms cloud? And that data will be downloadable into Windows & Excel where I can then manipulate it?

Then there’s a big problem. The 3-phase sketch for the emonTx doesn’t have the pulse counter built in, you’ll need to add it and you’ll need to adjust the settings and calibration too, and you need to upload it as it’s not the default. There’s a pulse count inside the emonPi, but it will report separately to emoncms. (i.e. you’ll have the nett grid power from the emonTx, and imported energy from the pulse count.)

That would indeed need a custom script that runs on your Pi.

The pulse count from the emonPi will be there, but separate. A pulse count from the emonTx, if you add that, is a small configuration change via your browser.

What emoncms cloud? Unless you decide to send the data to both (another configuration change via your browser), your data normally stays inside your RPi and is saved inside the emoncms running in there.

Somebody else will need to answer that. Most people set up dashboards and view it as web pages generated by the RPi, or emoncms.org, or both.