External Transfer Switch - Multiplus 8, 10 and 15kW

Q&A and troubleshooting
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1

I am trying to get my head around the new External Transfer Switch method used to parallel the 8, 10 and 15kW multiplus 2.
Overall, it looks like a great option with reduced AC wiring, Multiplus rather than the more expensive Quattro and they fact that we would no longer need a bypass switch.
My understanding so far:

AC Out is used for all Power, In and Out
Special firmware needed
Both 3 phase and Parallel configuration
AC In is just used as a voltage sense input, so only needs to be 1.5mm2
Both Grid disconnect and Earth-Neutral bond is via external relays in this configuration
Will operate as Off-grid (no grid code) and ESS (with grid code)

I have a few questions for anyone that has done this:

  1. A 20 meter limit is suggested between meter box / main distribution point and the Multiplus setup. Is this due to the voltage sense and/or current transformer measurement cable length restrictions? If so can a ET112 be used to over come this, and if so for V and I?
  2. Will functions like, ’ignore AC in’ to force the system off grid as needed still work?
  3. Will item (2) above work with Generator Assist as a workaround for scheduled charging

Thanks for any input,

Simon…

2

I have now drawn this up for a single phase 2 x 15k Multiplus. Looks good, the 20m limit is a pain, this is due to the current transformer [I could do with 30m].

Any real world feedback from anyone, especially the change over time between pass through grid connected to inverter power and back to grid pass through? Using the internal relays its pretty instant, same for the external?

Thanks,

Simon…

3

Unfortunately no feedback.
I am also in need of knowing if the CT is obligatory for external transfer or if an external power meter can fulfill the ‘CT’ measurement.

This would take away the 20m max restriction for the CT cable.

4

I have a feeling these will be too slow.
It is a common complaint even in normal ESS applications

5

I have some questions and remarks regarding this topic as well.

  • Is it allowed to use a gridmeter (EM540 in my case) with this way of system design?’
  • According to the manual, with some grid codes, a Ziehl relay is mandatory, but I am unable to find anything regarding that rule in the available documentation here in NL.
  • I can not comprehend that grid operators certify the MP II for use on the grid without the Ziehl, but do not certify it with the external transfer. The logic in the MP II remains the same.
  • In the same manual, if you follow the drawings, the version without the external Ziehl relay only has a single contactor to separate the supply from the internal system. I would argue that that would be sufficient in case of a generator as only mode of supply, but when connected to a grid without the need for a Ziehl, you’d have to put two contactors in series for a proper separation. Same as the MP II internal grid relays.
  • Judging by the available I/O on the RS series, the external transfer switch will never be available for the RS. Which is too bad, because it simplifies cabling in an existing installation quite significantly.
  • As a bit of a stretch, I would propose an improvement on this firmware: To persuade the various grid operators that mandate the Ziehl to loosen that €800 requirement, use the Aux inputs to reed the feedback of the contactors. One for the grid connection and one for the ground relay. And if one of the feedback signals comes to late, switch off the inverter. And put 2 contactors in series for the grid.

I sure hope Victron will invest some more dev-time in this branch of the eco-system. I see potential there.

6

Also NL…
I am going to test the setup with the S99 fw first without the Ziehl.
I need an contactor that is quick enough to switch in the time the MP gives the signal to it after syncing.