RCD trippig and inverter is not able to go back to on grid mode

Dear Friends,
I hope i will find some solution with you.
I have installed a system with Goodwe inverter GW10k-ET, hybrid it has 9.3 kwp modules and 6.4 High voltage BYD battery box.
This is the situation:

We turn on the whole system, everything works perfectly, now we want to simulate a blackout so we switch off the grid on main switch of the house the inverter immeditaley goes off grid and supply the house without interruptions, BUT, when we bring back the grid and inverter tries to go "on grid mode" from "off grid mode" it trips the RCD of the house.

And then in order to bring back the grid we have to restart the inverter, so it starts with on grid mode.
the inverter has two output 1.on grid and 2. back up, mos of the house is on backup but not the heating system and the kitchen in order to not overload the battery in case of a blakout.

I really hope someone can give me some explanation im stuck with this system,




Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    I guess you are in Serbia or Albania?

    I am sorry for the long/complicated (and in English--my only language :/  ) answer. Neutral/Ground bonding is a complicated issue with Hybrid inverters and backup generators in the USA, and I do not know anything about your Utility power wiring. So, here we go... Please feel free to ask questions (even if you think they are obvious questions). Both of us need to be clear about exactly what is happening.

    I don't know anything about your power system... Single phase 230 VAC 50 Hz?

    Assuming that your have a "ground bonded neutral" from the pole/utility transformer (in the USA, typically the transformer neutral is created by grounding the neutral at the transformer at the pole, and again the Neutral and Ground wire is bonded in the main panel. And ground+neutral is not connected anywhere else.

    In the USA, we have a GFI (ground fault interrupter breaker) that plugs into the main AC bus bar, and then sends a "GFI protected" Hot+Neutral to the remote loads (typically kitchen, bathroom, external outlets that are near pool/wet areas). If there is a connection between Hot and earth ground (or to a degree, even between neutral and earth ground), the "leakage" current trips the GFI (RCD in European terms).

    We don't have an RCD for the whole home (which I think is done in Europe). So, assuming you have no other issues (short circuits, wet wiring box, etc.), I wonder if you are getting a connection (short circuit/fault/wiring error) between a Neutral (is that the brown wire in your region?)... That will not trip an over current breaker, but can trip an RCD/GFI type breaker (assuming neutral is a few volts above ground--not uncommon voltage drop)... The slight voltage above ground can cause enough current to trip a GFI breaker. 

    Country by country codes differ... If you have a mains breaker (master breaker from utility power) with RCD... I think it has a trip value of 300 mAmps (0.300 Amps AC). And if you have branch circuit RCD breakers, they are typically set to 30 mAmps (0.030 Amps)--I think.

    So, I think I need to know more about your wiring (mains, branch circuits, multiple RCDs, etc.). Is it the main house RCD breaker (300 mAmp) that is tripping, or is it the branch circuit to your Solar Power system (300 or 30 Amp RCD)?

    In any case, I would use a Current Clamp DMM (Digital Multimeter) and clamp both "hot and return" (the current carrying wires) and measure the "leakage current" in each pair (an RCD and Current Clamp meter around both power wires--If the current out equals the current in, the "total current" in the clamp is zero amps. If one leg is carrying more current than the other, the RCD/Clamp meter will see the difference, and if the difference is >300/30 mAmps, it will trip the RCD Breaker).

    https://www.amazon.co.uk/s?k=current+clamp+meter&ref=nb_sb_noss

    Note: There are both AC Current Clamp DMM and AC/DC Current Clamp DMM. The AC current clamp can only measure AC current--Which is perfect for what you need to do here. An AC/DC Current Clamp DMM can be set to measure AC or DC current--These meters are very handy for measuring/debugging/understanding DC power systems (solar power system, vehicle electrical systems, etc.).

    You need to check the specifications very closely... AC Clamp meters can also measure AC+DC voltages--Which can be confused with an AC/DC Current Clamp DMM which can also measure AC+DC currents.

    Anyway, with your system running normally, I would measure the Hot+Neutral current for each of your branch circuits and see if you can find leakage current--Which may be worse when you do the power fault testing.

    Also, see if you can contact your supplier/mfg. of the system... Sometimes they have knowledge of how to debug problems like this, or if their systems have issues with RCD equipped homes.

    In the USA, our inverters (if they are working/installed) per code, have to supply a Neutral+Ground bond when running in "off grid mode" and NOT connect Neutral+Ground when running in GT (or shore power) Mode. That is typically done with the AC transfer switch... 2 connections for Hot+Neutral, plus a 3rd connection for Neutral to Ground bonding. In GT mode, only H+N are transferred to the protected loads, in Off Grid mode, the Neutral is connected to Ground.

    If your Hybrid Inverter has a Neutral to Ground bond/connection when in Grid Tied Mode, that could easily trip an RCD breaker.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset