Trying to get to grips with the RCD tripping issue and get a solution.

Background:

I recently installed a 5kW SunSynk Inverter with a Hubble AM2 5.5kW Lithium battery for a friend. All are working except that the RCD feeding the Inverter trips when the Inverter switches back to the Grid. I did some test and I recon I know what the issue is.

Below is my take on the problem and some options to work around it. I will appreciate any input as I can't test until July as I am out of Country. I am not an Electrician but electronics is my bread and butter.

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Disclaimer: My understanding of the fault maybe wrong and the suggestions listed here is not tested at all. The diagrams are just for illustration purposes with just the basic elements. No Surge Protection devises, etc are shown.

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Note: There should always be an Earth - Neutral bond on the Grid Feed. When the Inverter is in "Island Mode" it will not draw power from the Grid and therefore the Inverter Feed RCD can’t trip when the Inverter is running in Island Mode.

 

Figure: SunSynk Inverter ATS240V output controlling the Earth-Neutral-Bond-Relay switching as recommended by SunSynk.

1: GRID Power is UP: When the Grid is UP (live) the Earth-Neutral bridge will be at the Grid. The Inverter's ATS240V signal will be off and the Earth-Neutral-Bond-Relay de-energized. . All OK

2: GRID goes down: When the GRID power goes down, the Inverter will energized the Earth-Neutral-Bond-Relay. The Earth-Neutral bond will now be at the Output of the Inverter that will also supply power to the Essential Loads. . All OK

3: GRID restored: When the Grid comes back ON the Inverter will take 1-2 minutes before it will switch back to the GRID.

    a: During this time the Inverter will still generate power for the Essential Loads with the Earth-Neutral Bond at the Output of the Inverter.

    b: When the Inverter switch back to the GRID it will also disconnect the Earth-Neutral Bond at the Inverter Output (ATS 240V signal goes OFF). All should be OK provided the Earth-  Neutral bridge and Power transfer happen at the same instance.

With my Installation the Inverter Feed RCD trip every time at this point.  This is with SunSynk Firmware version; MCU:3374

I manually cut the Earth-Neutral bridge just before the Inverter reverted back to the Grid as a test. That will prevent the RCD from tripping. That proves to me that the ATS240V signal is a fraction too late (for my install and many others it seems).  According to this video by Keith https://www.youtube.com/watch?v=QtDblj7MMjY (at 2m15sec) he mentioned a delay is programmed in. I am not sure if that delay is when the Grid goes down or come back on, or both. 

In my opinion SunSynk should add another setting in the Software where one can adjust/optimize the ATS signal timing vs Changeover time.

 

It seems these are the main solutions that the installers go for

No RCD that feeds the Inverter

Use the Grid Feed to control the Earth Neutral Bridge Box supplied.

 

Notes on the above:

No RCD:

Simple solution and not a requirement because of downstream RCD's? BUT, the Sunsynk Operators Manual recommends a Type A, 30mA instantaneous, 2 pole RCD feeding the inverter. Keith from SunSynk also mentioned that an RCD should be fitted. As I am familiar with most of the electronic components that are involved within an Inverter I understand why SunSynk insist on one. Your choice, I would not go without an RCD.  I could not find a Type A anywhere, nether mind a sales person that know that there are different types. However  I don’t think that not using a Type A is the problem.

The Earth-Neutral Bridge Box:

When the Grid comes back ON the Earth-Neutral bridge is immediately broken while the Inverter still provides current to the Load until it switch back to the Grid. During that 1 - 2 minutes there will be no Neutral bridge (floating Neutral) until the Inverter switch back to the Grid!

 

Workarounds:

Figure: Workaround 1

Workaround 1: GRID Feed controlling the Earth-Neutral-Bond-Relay switching

The GRID voltage controls the Earth-Neutral-Bond-Relay. The moment the Grid goes down the N/C contacts closes bridging the Earth and Neutral at the LOAD output of the Inverter. . All fine.

But, when the Grid comes back ON this bond is immediately broken while the Inverter still generates the current until switchover time (1 - 2 minutes). That will result in a floating Neutral until the Inverter switch back to the Grid! (not OK)

 

Fig: Workaround 2a

Using a Changeover Contactor switched by the Inverter's ATS240V signal

 

When the Grid is UP there will be no output from the ATS240V, so the Earth-Neutral-Bond-Timing-Contactor will be de-energized. The Grid Power will then flow through the N/C contacts to the Essential Loads bypassing the Inverter. The Earth-Neutral Bond will be at the Grid Feed.

 

When the Grid goes down the ATS240V signal will energize the E-N-B-T-Contactor transferring the Essential Loads to the Inverter. The Earth-Neutral bridge is then at the LOAD output of the Inverter.

 

If the Grid comes back ON, for the 1^st minute or 2 the Inverter will keep on providing power before the ATS240V signal will fall away. The E-N-B-T-Contactor will then change back to the Grid.

 

Workaround 2b

Similar to 2a, except if 2 Contactors is used.

KLF_NBR_Trip1.pdf

KLF_NBR_Trip2.pdf

Edited April 13, 20231 yr by FvA
Added Note that the Contactors must be mechanically interlocked

Hi @FvA I must say you have a very detailed  analysis here . But I am assuming that you have  connected your non-essential grid feed from after the MAIN ELD in your DB board , and hence it is this ELD that's causing the issues. While I am no expert in grid-tied configuration , not even by stretch of the imagination, I think that's wrong . Your non essential feed is bidirectional and when pushing power into the non essential circuits it should be tied after the MAINS breaker but before the MAINS  ELD. I hope I understand your configuration correctly.

 

EDIT : Your detailed schematics suggest I do understand correctly . Is that RCD (ELD) you have on the left also feeding the non essential circuits in your home ?

EDIT : But I do think you have anyway hit a nerve on the Sunsynk internal operation here . The machine should definitely negate the ATS240 output well in advance before asserting its gridtie internal relay. It clearly appears from your tests that it does not .  Which in practice means there is a short duration of time when the grid neutral is bonded at 2 instances , which is unwanted. 

Edited April 12, 20231 yr by BritishRacingGreen

12 minutes ago, BritishRacingGreen said:

Hi @FvA I must say you have a very detailed  analysis here . But I am assuming that you have  connected your non-essential grid feed from after the MAIN ELD in your DB board , and hence it is this ELD that's causing the issues. While I am no expert in grid-tied configuration , not even by stretch of the imagination, I think that's wrong . Your non essential feed is bidirectional and when pushing power into the non essential circuits it should be tied after the MAINS breaker but before the MAINS  ELD. I hope I understand your configuration correctly.

When the SunSynk is pushing  power onto the non essential side after the MAIN  ELD , its also effectively bypassing the MAIN ELD , and the ELD will not detect leakages as it should be .  Furthermore if  the Sunsynk is configured to export excessive power to ESKOM  , this power will flow in the reverse direction in the ELD , which also doesn't sound right  , and could cause some unwanted issues.

May be SS Gurus can help us out here.

Edited April 12, 20231 yr by BritishRacingGreen

re KLF_NBR_Trip 2 : for both workaround a and b , you will lose seriously out on un-interuptability . Your loads will feel the pain. 

Also , as per 2b , I believe you do require mechanical interlocking between the two contactors to pass COC. I know you are doing it electrically , but that is not considered safe enough.

15 hours ago, FvA said:

All are working except that the RCD feeding the Inverter trips

This is your problem , there should be no RCD before the inverter. They have configured the ATS240 signal on the newer firmware with a slight delay to prevent RCD tripping so its not from that. Also make sure you neutrals are split between essentials and non essentials.

23 hours ago, FvA said:

Trying to get to grips with the RCD tripping issue and get a solution.

Background:

I recently installed a 5kW SunSynk Inverter with a Hubble AM2 5.5kW Lithium battery for a friend. All are working except that the RCD feeding the Inverter trips when the Inverter switches back to the Grid. I did some test and I recon I know what the issue is.

Below is my take on the problem and some options to work around it. I will appreciate any input as I can't test until July as I am out of Country. I am not an Electrician but electronics is my bread and butter.

-------------------------

Disclaimer: My understanding of the fault maybe wrong and the suggestions listed here is not tested at all. The diagrams are just for illustration purposes with just the basic elements. No Surge Protection devises, etc are shown.

--------------------------

Note: There should always be an Earth - Neutral bond on the Grid Feed. When the Inverter is in "Island Mode" it will not draw power from the Grid and therefore the Inverter Feed RCD can’t trip when the Inverter is running in Island Mode.

 

Figure: SunSynk Inverter ATS240V output controlling the Earth-Neutral-Bond-Relay switching as recommended by SunSynk.

1: GRID Power is UP: When the Grid is UP (live) the Earth-Neutral bridge will be at the Grid. The Inverter's ATS240V signal will be off and the Earth-Neutral-Bond-Relay de-energized. . All OK

2: GRID goes down: When the GRID power goes down, the Inverter will energized the Earth-Neutral-Bond-Relay. The Earth-Neutral bond will now be at the Output of the Inverter that will also supply power to the Essential Loads. . All OK

3: GRID restored: When the Grid comes back ON the Inverter will take 1-2 minutes before it will switch back to the GRID.

    a: During this time the Inverter will still generate power for the Essential Loads with the Earth-Neutral Bond at the Output of the Inverter.

    b: When the Inverter switch back to the GRID it will also disconnect the Earth-Neutral Bond at the Inverter Output (ATS 240V signal goes OFF). All should be OK provided the Earth-  Neutral bridge and Power transfer happen at the same instance.

With my Installation the Inverter Feed RCD trip every time at this point.  This is with SunSynk Firmware version; MCU:3374

I manually cut the Earth-Neutral bridge just before the Inverter reverted back to the Grid as a test. That will prevent the RCD from tripping. That proves to me that the ATS240V signal is a fraction too late (for my install and many others it seems).  According to this video by Keith https://www.youtube.com/watch?v=QtDblj7MMjY (at 2m15sec) he mentioned a delay is programmed in. I am not sure if that delay is when the Grid goes down or come back on, or both. 

In my opinion SunSynk should add another setting in the Software where one can adjust/optimize the ATS signal timing vs Changeover time.

 

It seems these are the main solutions that the installers go for

No RCD that feeds the Inverter

Use the Grid Feed to control the Earth Neutral Bridge Box supplied.

 

Notes on the above:

No RCD:

Simple solution and not a requirement because of downstream RCD's? BUT, the Sunsynk Operators Manual recommends a Type A, 30mA instantaneous, 2 pole RCD feeding the inverter. Keith from SunSynk also mentioned that an RCD should be fitted. As I am familiar with most of the electronic components that are involved within an Inverter I understand why SunSynk insist on one. Your choice, I would not go without an RCD.  I could not find a Type A anywhere, nether mind a sales person that know that there are different types. However  I don’t think that not using a Type A is the problem.

The Earth-Neutral Bridge Box:

When the Grid comes back ON the Earth-Neutral bridge is immediately broken while the Inverter still provides current to the Load until it switch back to the Grid. During that 1 - 2 minutes there will be no Neutral bridge (floating Neutral) until the Inverter switch back to the Grid!

 

Workarounds:

Figure: Workaround 1

Workaround 1: GRID Feed controlling the Earth-Neutral-Bond-Relay switching

The GRID voltage controls the Earth-Neutral-Bond-Relay. The moment the Grid goes down the N/C contacts closes bridging the Earth and Neutral at the LOAD output of the Inverter. . All fine.

But, when the Grid comes back ON this bond is immediately broken while the Inverter still generates the current until switchover time (1 - 2 minutes). That will result in a floating Neutral until the Inverter switch back to the Grid! (not OK)

 

Fig: Workaround 2a

Using a Changeover Contactor switched by the Inverter's ATS240V signal

 

When the Grid is UP there will be no output from the ATS240V, so the Earth-Neutral-Bond-Timing-Contactor will be de-energized. The Grid Power will then flow through the N/C contacts to the Essential Loads bypassing the Inverter. The Earth-Neutral Bond will be at the Grid Feed.

 

When the Grid goes down the ATS240V signal will energize the E-N-B-T-Contactor transferring the Essential Loads to the Inverter. The Earth-Neutral bridge is then at the LOAD output of the Inverter.

 

If the Grid comes back ON, for the 1^st minute or 2 the Inverter will keep on providing power before the ATS240V signal will fall away. The E-N-B-T-Contactor will then change back to the Grid.

 

Workaround 2b

Similar to 2a, except if 2 Contactors is used.

KLF_NBR_Trip1.pdf 70.33 kB · 8 downloads KLF_NBR_Trip2.pdf 58.67 kB · 6 downloads

Just added the full diagram of the Installation. No PV panels yet so the AUX out is for future use. No load on it.

 

KLF3.pdf

Edited April 12, 20231 yr by FvA
Wrong Type RCD's

2 hours ago, BritishRacingGreen said:

When the SunSynk is pushing  power onto the non essential side after the MAIN  ELD , its also effectively bypassing the MAIN ELD , and the ELD will not detect leakages as it should be .  Furthermore if  the Sunsynk is configured to export excessive power to ESKOM  , this power will flow in the reverse direction in the ELD , which also doesn't sound right  , and could cause some unwanted issues.

May be SS Gurus can help us out here.

Good day BritishRacingGreen

Thanks for your reply, I appreciate it. I uploaded the layout as I installed it to clarify some issues. The Inverter is not configured to push power back to the grid. I have a value of 100W from the grid.

1 hour ago, BritishRacingGreen said:

re KLF_NBR_Trip 2 : for both workaround a and b , you will lose seriously out on un-interuptability . Your loads will feel the pain. 

Also , as per 2b , I believe you do require mechanical interlocking between the two contactors to pass COC. I know you are doing it electrically , but that is not considered safe enough.

Agree with you. My 1st option is to wire it as SunSynk propose, if they sorted the timing. On top of that it it ads to the costs.

Yes, thanks for pointing that out to me. I actually have a changeover mechanically interlocking contactor with NC's contacts (but only 25A). I looked at the Hager 63A ESC263U for Option 2a. Changeover time 20ms open and 25ms close.  

1 hour ago, Nexuss said:

This is your problem , there should be no RCD before the inverter. They have configured the ATS240 signal on the newer firmware with a slight delay to prevent RCD tripping so its not from that. Also make sure you neutrals are split between essentials and non essentials.

Hi Nexus, thanks for your feedback. I uploaded the complete wiring diagram. I know it is not a requirement for the RCD in front of the Inverter, but I will not go without. You will note that I have a RCD just for the Non Essentials, one for the Essentials and another for the AUX feed.

Yes, I saw the Video where Keith from SunSynk mentioned the slight delay. But that might be when the Grid fails. One certainly do not need a delay when the Inverter switch back to the Grid. Rather a fraction before Changeover. I tested that by manually disconnecting the ATS Signal to the Earth Neutral Bond Relay around 60 seconds after switching ON the Grid. About 10 seconds later the Inverter changed back to Grid. During that 10seconds there was no Earth-Neutral bridge. The RCD did not trip as there was no Earth-Neutral bond.  

And that brings me to another option I had in mind: a Delay ON adjustable Timer that can do that that one can set as close to the point that the Inverter Change back to Grid. The problem is I do not know how much the time will vary. I suspect the Inverter is synching it's frequency and Voltage to the Grid before changeover. On top of that is it a gradual feed in of Power or a sudden changeover?

For my next visit I will take 2 small Isolation Transformers with and hook it up to my Oscilloscope to see what is happening when.     

In the sunsynk inverter grid settings there is a setting for 'reconnection time', and 'ramp rate', default is 60 seconds. May help you? 

Edited April 12, 20231 yr by abd7

38 minutes ago, FvA said:

Hi Nexus, thanks for your feedback. I uploaded the complete wiring diagram. I know it is not a requirement for the RCD in front of the Inverter, but I will not go without.

You have to it will always be tripping if you dont. I tried it aswell lol. RCD before non essentials and essentials is all you need. You cant have hybrid inverters like these after an RCD it must be before.

Edited April 12, 20231 yr by Nexuss

51 minutes ago, abd7 said:

In the sunsynk inverter grid settings there is a setting for 'reconnection time', and 'ramp rate', default is 60 seconds. May help you? 

Did not change that as I think that is the time it will take before it will change over. To make sure the Grid is stable. The actual changeover happened when I tested 10 seconds after that. The problem lies in my view the instance when the Earth-Neutral bond breaks (ATS signal) vs when the Inverter switch back the Load to the GRID.

29 minutes ago, Nexuss said:

You have to it will always be tripping if you dont. I tried it aswell lol. RCD before non essentials and essentials is all you need. You cant have hybrid inverters like these after an RCD it must be before.

I did bypassed the RCD for now🙄. I am committed to get it sorted

 

Keep in mind that Keith explains things from a UK perspective. They have different legislation and requirements compared to us. The way the grid operates is also probably different.

My install only has the main 63A CB on my Eskom-in, and then the inverter has a 32A MCB on its own input. RCDs are installed for the plugs bus in my house DB and in the Garage DB. Permanent E-N bond after the inverter output. 

If you have none-essentials installed on the grid side of the inverter, install an RCD towards those loads instead of towards the grid. I reckon then you will always get the protection you are after. I might be wrong, but I believe there is not a requirement for fixed-wire installations to have RCD protection. I had the installer redo my DB while they were busy with my solar, and my stove and oven are upstream of the RCD, and the geyser currently has no RCD fitted either.

I asked the installer about the E-N bond thing (I was one of those customers who studied the manual front-to-back and watched all the videos before my installation started. He must love me), and he tried explaining something about "in SA the grid does not have earth leakage detection" or something like that. Maybe he meant on the street level there is no E-N bond, and therefore an RCD before the inverter might not work as expected. Not sure. 

2 minutes ago, suds7162 said:

Permanent E-N bond after the inverter output. 

Just a heads up , you need to do that via a relay and ATS 240 port/signal from inverter if you are running a sunsynk/deye.

30 minutes ago, Nexuss said:

Just a heads up , you need to do that via a relay and ATS 240 port/signal from inverter if you are running a sunsynk/deye.

I'm not sure why though. The manual is a little ambiguous about this to be honest. My interpretation is that the E-N bond via relay is only required if you have an RCD installed upstream of the inverter. Since that's not the case for (what appears to me anyway) most installations in SA, such a relayed bond is not required?

Sunsynk's own diagram for SA specific wiring does not mention anything about a relay, or an RCD upstream, and it indicates a permanent E-N bond:

Looking at the diagram now I realize I made a mistake in my previous comment. 

I'm pretty sure that my permanent E-N bond is on the grid side of the inverter, not the load side. I'll have to pull out the DB board to double check.

Report back on the Issue

 

I emailed a copy of the issue I posted here to SunSynk Support. They came back to me today, that I was spot on with the reason and that they implemented a quicker disconnect of the ATS240V signal in later firmware. My Unit firmware is MCU3374. I will upgrade the MCU and COM firmware when I am back late June.

 

So all should be good

Note that the Draft copy if have of SANS 10142 says

5.2.5 Point of Generator Connection (PGC)
The Point of Generator Connection (PGC) serves as the point across which a generator is synchronised to the Utility and / or other generators, or where an islanded bus is powered. The PGC serves as the point where the embedded generator(s) disconnect from the rest of the electrical Network.

The PGC cannot be installed downstream to an earth leakage device.