ESS Bypass switch for n-1 nonstop system use

DIY
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1

For a 24/7 nonstop application using one or more Multiplus ESS, I had some thoughts about a bypass switch what is diffrent to ordinary 1-0-2 model.

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Schematic shows two ESS A and B what are equal mirrored. The bottom connection “Verbundnetz” is public grid. The red line is a private microgrid. Each ESS uses AC- In and AC-Out busbars. The ESS symbol itself equals the symbol printed to the front panel of all Multiplus. Out2 ist not in use. Out1 is simply named Out.

The following point only require to consider one of the two ESS.

1
For ordinary operation external AC-Out und AC-In contactors are open while the external NAS contactor is closed. ESS tries to sync with the public grid and closes its two internal contactors after success. Power on both busbars AC-Out and AC-In might be bidrectional. The load on Out bus could also be any additional AC coupled inverter (maintaining the 1:1 rule). The In-Bus also allows to charge battery from grid or feed in to grid.

2
Now, the AC-Out contactor of ESS-A closes what powers up the red microgrid line. This allows to use ESS-B as a slave supplied by ESS-A. For the case of public grid failure at ESS-B, it could be supplied by ESS-A if NAS_B is open and AC-IN-B is closed. For opposite direction, it is possible to close OutB and InA.

3
The critical thing is, what happens if AC-In and AC-Out contactor of the same ESS will close. With other words: We make a connection between Multiplus AC-In and AC-Out. My theory is, that this is allowed, as long as the internal contactors of the Multiplus are also closed. As public grid could fail in this situation, it is not allowed to use that state for a longer timer. The internal Multiplus contactor could not disconnect from public grid like required by any national grid rules. if this happens unexpectedly, probably the Multiplus simply goes to AC overload protection. It is not strong enough to feed the public grid.

So far nothing dangerous should happen, if we connect AC-Out to AC-In for a single ESS. The reason of doing this is, that this state allows to disconnect the Multiplus without any interrupt of the loads connected to the AC-Out busbar.

To replace the Multiplus without interrupting the supply at AC-Out busbar, things become more difficult. Never connect Multiplus AC-Out to any other AC source, what might be out of sync. We have to keep the following sequence to assemble the ESS again

a) connect Mulitplus AC-In to AC-In busbar Then wait until internal Multiplus contactors close after sync
b) connect the Multiplus AC-Out ot the AC-Out busbar
c) open AC-Out contactor and if independend operation required AC-In contactor too.

We are now back at ordinary ESS operation described in 1) The loads of AC-Out busbar are now supplied by a diffrent Multiplus hardware while there were no interrupts for the reason of new Multiplus hardware installation. Will this work like described?

Some minor things are evident:

  • never close In-A and In-B same time, as this will parallel the electricity meters of both houses with unexpected results of meassurement what depends by cable resistance.
  • never close OutA and Out-B same time, as the Multiplus of diffrent ESS do not have VEBus link to snycronize the phase for array operation
2

Who is able to operate this, its potentially dangerous!

I would not build this, one mistake and you will destroy your system.. not supported or intended use case by victron

Are you also 100% sure grid for both houses is the same phase?

3

That was not the question. Those who built it should be able to operate. Logically those installations are not supported by Victron why I did this post in the DIY section.

Both houses are 3 phase. Schematic is simplified. One house has own transformer what is Dy5. This way, even private an public transformer could be paralleled. For self made projects, it is possible to lock dangerous sequences and states. Switches of transformers are also not locked. For this reason you need license or switching authorization what allows you to use the switches.

Anyway this was not the question. Even if both houses are diffrent phase from Dy5 / Dz0 combination it is possible to use the system correct and redundant.

4

This is pushing the boundaries of what we would encourage to be posted in diy. You really need to consult a qualified supplier.

5

What is the purpose of the system?

  • UPS only?
  • Peak shaving?
  • PV feed in?

Maybe you cold design a micro grid that is not AC couple to the grid.
Then add PSUs to recharge the DC-bus of the two batteries from grid, giving two recharged clusters in a Victron micro grid.
This design would not be able to feed back to grid and has limited power from grid.

But you need to get in contact with a very experienced Victron installer. Micro grid is a new feature.

6

It will work, but i would not take the risk..

7

You forgot the two grounding relais!

If the grounding relais is on at in erting mode, you have a shortage between N and PE!

This will show interesting effects. So in the microgrid mode nothing should be connected on the ACout!

8

The purpose is building resiliency by cooperation of more than one ESS. The given circuit should also allow flawless sharing of any Diesel block-type thermal powerstation from other house.

Up on now, there is no comment about “not possible because…”. I am going to try the intended operation with my small system myself. If successful, the “big system” will become my neighbour.

The German ministry of energy will introduce extra prosumer tax for photovoltaik owners. Therefore grid defection is unfortunately the only consequence for some DIY end consumer communities.

We already have a local 48V DC grid with line length up to 40m for LED illumination. Reasonable energy amounts from and to the neighbours house is only possible by AC line of about 100m.