IT grounding system with Quattro 230 V 48/10000

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jontm asked Jan 27, '22

IT grounding system with Quattro 230 V 48/10000

Hi!

We have a combination of IT and TN grounding systems in the country where i live.

Most of the older parts of the grid uses a IT system. This method of grounding is also used in genset applications and maritime emergency generators, however then often with a delta secondary instead of star which is shown in the image bellow.

In effect you either have L1 (230 V) and N (0 V) for single phase or you have L1 (130 V) and L2 (130 V with a 120 degrees phase shift) with no neutral available.

I have a Quattro 230 V 48V/10000VA unit that i am planning to use on a cabin that has 230 V delta connected secondary from the genset that is currently being used. That means that there is no netrual in the power system. Equipment is grounded with a separate PE conductor connected to local ground (literally a buried mesh or spear). A ground fault interrupter is mounted in the main fusebox (or should be per regulations) to ensure that breakers are tripped if equipment shorts to ground. This is due to the ground fault currents in such a system will be too small to trip the MCB.

I cannot find any information on the use of the Victron Quattro in such power grids, would it take damage or trip some protection features if I were to connect L1 and L2 to the input side of the unit ?

Will operation of the unit will be similar to what is described as option 3 in the user manual just without the autotransformer on the output (image attached) ?

Option 3.JPG

MultiPlus Quattro Inverter Charger Grounding

different-ac-power-systems-tn-tt-it-earthing-1.jpg (40.5 KiB)

option-3.jpg (260.8 KiB)

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Modifications Space

Node Red Space

Answer 1 · 2022-01-27T17:57:41Z

Alexandra answered · Jan 27, 2022 at 05:57 PM

@jontm

The inverters have / need a Neutral for grounding. There is a relay internally that connects the neutral to the earth. So having to lives in will not end well.

https://www.victronenergy.com/media/pg/MultiPlus-II_GX/en/installation.html#UUID-b8310945-a1c7-2bfd-5f57-c494fa312015

Have you tried contacting a local Victron Dealer. they most likely have creative solutions for the mix of the different systems. Local laws regulations being important to follow, it is best to source local knowledge on this one as most countries do not use that type of set up anymore or ever.

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jontm commented · Jan 27, 2022 at 10:46 PM

The manual states that this internal relay can be disabled.

Take a look at this example with split phase on the 230 V Quattro. Here you have L1 and L2 going in to L1 and N on the Quattro (two lives). On the output L1 and N goes into an autotransformer, but the output of the Quattro is not grounded internally, but rather on the center tap of the autotransformer. The so called "option 3" that i linked above from the manual have wording that seem to indicate that the external autotransformer is only an optional feature in case you need 120 V from a 240 V split phase input.

https://www.victronenergy.com/upload/documents/AT-1-split-phase-240V-to-120-240V-with-Quattro-240V.pdf

The manual states that the internal ground relay is always disconnected before the input switches are closed, therefore there should in theory at least not be an issue with L2 being shorted to ground through the internal ground relay. And based on this application example, the Quattro should clearly be able to deal with two lives in. 230 V in an IT system have similar potentials to a 240 V split phase. The main difference being that on 230 V IT there is a 120 degrees phase shift between the phases and not a 180 degrees phase shift as one would have on a American type split phase.

I have also contacted suppliers locally to get an answer on this, have not yet received an answer, but IT and TN is used interchangeably where i am from. Most have no idea if the mains in the house are a TN system or IT system. They are treated the same in the fusebox. Both if you have a TN system in your house or apartment, the N phase is treated as a L2 and if you have IT, L2 is treated as N. Both are fused anyway. If you come here with a Quattro installed on a vessel, you would have no idea if the shore connection would be IT or TN grounded (no idea if the neutral is live or not). If the Quattro would not be able to deal with that i would assume that the Quattro would not be sold where i am from, but it is quite common.

Is it something I am misunderstanding here ?

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Answer 2 · 2022-01-27T18:08:25Z

wkirby answered · Jan 27, 2022 at 06:08 PM

Another option my be to use an isolation transformer to take in L1 - L2 on the primary.
The the secondary can be wired with neutral bonding at the isolation transformer secondary and earth stake to make a nice TNS system with 230V Line Neutral and Earth to then feed to the Quattro.

https://www.victronenergy.com/upload/documents/Datasheet-Isolation-Transformers-EN.pdf

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jontm commented · Jan 27, 2022 at 11:05 PM

Yep. That is possible, but i do not understand technically why it is needed. IT and TN systems are used interchangeably in Norway. Only way to know if you have a live neutral or not in your have is to whip out the multimeter and measure. A considerably large part of houses and industrial buildings have live neutrals (or technically L2 instead of a neutral).

Based on this application example from Victron: https://www.victronenergy.com/upload/documents/AT-1-split-phase-240V-to-120-240V-with-Quattro-240V.pdf

It seems like the Quattro should not care that much if the N input terminal have a live potential or not as long as the voltage between the L1 and N terminal does not exceed the rated voltage of the input terminals. Based on the manual as well, it seems like the internal grounding relay is always opened before closing the input switches. Therefore connecting L2 to N should not cause a short in the grounding relay.

The only potential issue i can see is that the grounding system of the cabin would effectively switch between having a TN and IT grounding system depending on whether the genset is live or not. That should however not really matter as for the connected equipment the voltage between the two wires would be 230 V 50 Hz anyway. The N conductor to the cabin is not grounded as there are no N conductor today, only L1, L2 and PE. All MCBs open both L1 and L2 (this will be N when inverter is active). In the fusebox the MCBs will trip on ground fault the same way as before. They just measure the sum of currents (L1 + L2(N) < 30 mA)

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wkirby ♦♦ jontm commented · Jan 28, 2022 at 07:43 AM

Thank you for the additional information. With the downstream circuits arranged like you say, then switching between TNS and IT should not be a problem, this was my main concern.

Also the Quattro can accept an input with two lines. It is not necessary to have a ground referenced conductor here. Ground relay will open before the backfeed relay closes.
There is no phase angle as there is only one phase presented to the Quattro.

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jontm wkirby ♦♦ commented · Jan 28, 2022 at 09:27 AM

Great. Thanks. I have also contacted the local distributer, i am sure they have encountered this before. I am a electrical power engineer and do RnD on inverters for a living, but it is hard to know exactly how the internal protection functionality and software is setup.

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