Neutral/Earth bonding relay Goodwe ES inverters

[___]

On 2020/02/08 at 4:21 PM, Fuenkli said:

1. do nothing. What is the risk?

In my estimation the risk is low. Your neutral becomes a "hot" conductor (one might say), but if touching it causes enough current to flow to exceed 20mA-30mA, the RCD will still trip. With that said, I must still note that this would not be SANS compliant. SANS requires an islanded system to bond T and N.

On 2020/02/08 at 4:21 PM, Fuenkli said:

2. Permanently bond neutral to earth on the back up output. If I remember correctly this is illegal because it creates a second neutral earth bond

3. Connect the inverter in and out neutrals. Probably also illegal because you loose the earth connection when the grid is down or the main switch is switched off.

Both these are not allowed by SANS. Bridging the neutrals would probably be the lesser evil, 1) because Goodwe advises that you do this, and 2) apparently it is allowed in Australia. You won't lose the bond when there is a grid outage, but you might if your main breaker trips (which disconnects the neutral) or if you switch it off for any reason. Probably better than nothing, but not perfect.

On 2020/02/08 at 4:21 PM, Fuenkli said:

4. Install an external bonding relay. I am not sure how one would do this and how much this would cost. 

In my view this is the only proper way to do it, and ideally one would want the inverter itself to signal this (like the bonding relay box that's turned on by the internal relay in the Axpert). Only, I don't think the Goodwe has any way to signal such a relay.

One potential way is to use a contactor with 2 x N/O and (at least) 1 x N/C contacts. Use the two N/O contacts to switch the grid to the inverter, and the N/C to make a bond on the output. Let the grid pull in the contactor, that is, when there is a grid outage the contactor drops out.

The reason for actually switching the grid connection through the contactor is to mechanically interlock this operation: It would be impossible for the bond to be applied if the grid isn't also disconnected.

Downsides to this scheme:

1. If the voltage is out of range, but high enough to pull in the contactor, the inverter might switch to islanding mode while the bond remains unapplied.

2. NRS097 mandates a 60 second monitoring window after the grid returns. If the voltage/frequency remains stable in this 60 seconds, the inverter will connect back to the grid. The trouble with this: When the grid returns the bonding is removed, but for another 60 seconds the output will remain floating.

Which gets me back to my point that ideally, one would like the inverter itself to signal islanding mode in some manner.

[Fuenkli]

9 hours ago, plonkster said:

Which gets me back to my point that ideally, one would like the inverter itself to signal islanding mode in some manner.

thank you very much for the answers. It is very helpful. Because the Goodwe inverter can not signal islanding mode there is really no solution to solve this problem to comply with SANS.  I will take this up with Goodwe and advice.

[Halcyon]

@Fuenkli did you ever get feedback from Goodwe on this issue?

[Fuenkli]

2 hours ago, Halcyon said:

did you ever get feedback from Goodwe on this issue?

no I did not . Never received a reply to my follow up e-mail (see below). Based on @plonkster's very good summary and risks of the available options I have bridged the neutrals.

 

Dear David,
thank you for the reply. According to SANS, bridging neutral/earth is
illegal. We had a long discussion on "Power Forum" how to solve this problem
(see below). What do you suggest we do?
Regards
Juerg
 

On 2020/02/08 at 4:21 PM, Fuenkli said:
1. do nothing. What is the risk?
In my estimation the risk is low. Your neutral becomes a "hot" conductor
(one might say), but if touching it causes enough current to flow to exceed
20mA-30mA, the RCD will still trip. With that said, I must still note that
this would not be SANS compliant. SANS requires an islanded system to bond T
and N.

On 2020/02/08 at 4:21 PM, Fuenkli said:
2. Permanently bond neutral to earth on the back up output. If I remember
correctly this is illegal because it creates a second neutral earth bond
3. Connect the inverter in and out neutrals. Probably also illegal because
you loose the earth connection when the grid is down or the main switch is
switched off.
Both these are not allowed by SANS. Bridging the neutrals would probably be
the lesser evil, 1) because Goodwe advises that you do this, and 2)
apparently it is allowed in Australia. You won't lose the bond when there is
a grid outage, but you might if your main breaker trips (which disconnects
the neutral) or if you switch it off for any reason. Probably better than
nothing, but not perfect.

On 2020/02/08 at 4:21 PM, Fuenkli said:
4. Install an external bonding relay. I am not sure how one would do this
and how much this would cost.
In my view this is the only proper way to do it, and ideally one would want
the inverter itself to signal this (like the bonding relay box that's turned
on by the internal relay in the Axpert). Only, I don't think the Goodwe has
any way to signal such a relay.
One potential way is to use a contactor with 2 x N/O and (at least) 1 x N/C
contacts. Use the two N/O contacts to switch the grid to the inverter, and
the N/C to make a bond on the output. Let the grid pull in the contactor,
that is, when there is a grid outage the contactor drops out.
The reason for actually switching the grid connection through the contactor
is to mechanically interlock this operation: It would be impossible for the
bond to be applied if the grid isn't also disconnected.
Downsides to this scheme:
1. If the voltage is out of range, but high enough to pull in the contactor,
the inverter might switch to islanding mode while the bond remains
unapplied.
2. NRS097 mandates a 60 second monitoring window after the grid returns. If
the voltage/frequency remains stable in this 60 seconds, the inverter will
connect back to the grid. The trouble with this: When the grid returns the
bonding is removed, but for another 60 seconds the output will remain
floating.
Which gets me back to my point that ideally, one would like the inverter
itself to signal islanding mode in some manner.


 

 

[___]

It should be possible to make an internal modification in the inverter itself to make this possible. Probably not something you want to do while it is under warranty.

To the right of the diagram, the one marked "Relay array", technically you could solder a simple opto-coupler+resistor to the coil of that relay, and use the isolated switch side to signal something external. You really just want to know if that relay is open or not.

There might also be a way to build something that can sense this externally. The trick is to see if you can pass a current from the grid neutral to the backup neutral, and thereby test if that relay is open. If you use a completely isolated supply (about R25 or so for a discrete component that does everything), you can literally build a small detector that connects between those two neutrals. The other end simply feeds into an opto-coupler to make it completely isolated.

There is however still a small downside: Your bond will be engaged for a split second after "relay array" is closed again, the bond only drops out when the grid is reconnected. So for a split second you will have a double bond. That is probably much better than the solutions we suggested so far, and as long as there is no RCD on the input side it should work fine.

[Halcyon]

Thanks, I don't think my Sunsynk inverter will work properly with permanently bridged neutrals.?? It had a serious load power measurement issue until recently, which was resolved when we sorted out some common neutrals and earth fault problems between backup and non backup circuits etc.

I am thinking about going the contractor route to link earth and inverter output neutral.  At least the risk of non-compliance with SANS is reduced to 60 seconds only while inverter synchronises to the grid before reconnecting.  Load shedding seems to be a distant memory at the moment.  

Apparently Sunsynk are working on something to resolve this issue.  It might be in a software update which can send a signal to control a relay.  But where does one find a relay which would accept such a signal?

[___]

14 minutes ago, plonkster said:

a small detector

I maybe overestimating the simplicity of this. Nevertheless, the idea is sound (I think?). The trick, again, is passing a small DC current (it has to be DC, so it layers on top of any AC that might be there) through the loop and checking if it is possible. If it is possible, then the relay is closed, and you should open the bonding relay.

More effort than it is worth perhaps?

[Halcyon]

One could use a contactor as you suggest with a 60 second time delay on or off auxiliary add on. Then no need to get a signal from inverter. 

[Wetkit]

This is indeed an interesting subject. I am now learing of this with an existing Deye install, where the neutrals was joined on the input and output side of the inverter.

I have a Goodwe ES unit, but the way I understood NRS097, I installed a brand new earthing point at my house. This point was used for both the solar panels and the inverter. This ground point I join to my neutral on the output of the inverter. So far all working fine and no issues.

So, input side of inverter is using council earth and output is using new earth point at my house.

[giorgos]

The neutral line is Eskom's earth and the earth wire is the home's earth. It is safe to connect them together. At my house these 2 wires have always been connected together before the connection to the old rotary meter.  The rotary meter has been replaced with a prepaid meter to satisfy CoCT that I do not export any extra power from my solar installation

[Missing link]

A good example is victron that internally ensure disconnect and maitaning the bond.

With our utility supplies being ripped apart by theft we see higher and higher e-n elevations.

We had 430VAC running through our block a couple of weeks ago when the idiots stole the neutral and now sit with a 5-10vac elevation from the main supply.

Take a look at deye inverter suggested e-n bonding relay setup. On their site manual.

 

[Coulomb]

8 hours ago, Missing link said:

A good example is victron that internally ensure disconnect and maitaning the bond.

My understanding is that all Axperts have the extra contact that connects neutral automatically when in battery mode, starting some time in 2016. Growatts seem to have copied the design of the Axperts, so I expect them to be the same.

[PetCeres]

Does anybody out there resolved this nuisance ELU trips after grid power restores?It only trips the backup side. I do measure 93v between E and N.

thanks

[Coulomb]

8 hours ago, PetCeres said:

I do measure 93v between E and N.

I think that's the core of your problem, and this is unsafe. 

[PetCeres]

Yes

I drilled a 1.5 m earth spike into the ground with a big hammer outside the house and ground the inverter to it.

Later I tested a 2 pole 10 amp relay and put the same ground on one N/C contact and on the com side, the neutral of the backup side of inverter.

The N/O contact is wired to the N bar after main CB.

The coil of the relay is been wired to the grid L&N after main CB, so when grid fails, relay  de-energized, backup N is linked to new earth,93v floating is gone.

May this be safe enough?

Comment please!!!

[BritishRacingGreen]

2 hours ago, PetCeres said:

Yes

I drilled a 1.5 m earth spike into the ground with a big hammer outside the house and ground the inverter to it.

Later I tested a 2 pole 10 amp relay and put the same ground on one N/C contact and on the com side, the neutral of the backup side of inverter.

The N/O contact is wired to the N bar after main CB.

The coil of the relay is been wired to the grid L&N after main CB, so when grid fails, relay  de-energized, backup N is linked to new earth,93v floating is gone.

May this be safe enough?

Comment please!!!

@PetCeres Is this what you proposing above?

Edited November 14, 2021 by dropkick

[PetCeres]

Something like this:Only the Neutral.

[BritishRacingGreen]

1 hour ago, PetCeres said:

Something like this:Only the Neutral.

Ok @PetCeres, but does that neutral of yours comes from the Mains ELD , or is it wired before the Mains ELD?

Edited November 14, 2021 by dropkick

[P1000]

If your Goodwe ES is wired correctly (and with correct safety country), it does the neutral bonding itself. The unmarked terminal on the "back up" connection should be wired to ground in your DB.

 

On 2020/08/18 at 9:46 AM, ___ said:

@Weasel explained the other day that there is an unmarked terminal that you simply need to earth, and the bond will be made.

Apparently the reason they do it that way, is for flexibility. It allows you to connect that to a local earth spike (if so required in your area), or leave it unconnected and instead bridge the neutrals (TN-C-S setups), or earth to the council earth.

I've never seen one of these machines in the flesh, so you may want to check yours to be sure.

Edited November 15, 2021 by P1000

[BritishRacingGreen]

8 minutes ago, P1000 said:

If your Goodwe ES is wired correctly (and with correct safety country), it does the neutral bonding itself. The unmarked terminal on the "back up" connection should be wired to ground in your DB.

That is what makes me scratching my head, even my own humble Kodak MKSIII has it built in. 

 

Less it's a very very old model, I know nothing about Goodwe.

[PetCeres]

Missed @weasel thread,

Wired before the ELD.