Technical Support

Fault: The RCD upstream of the Inverter trips when GRID power comes back ON.

What I can get from the Internet, is that it is a common fault in South Africa in “Island Mode” if the Earth-Neutral-Bond Relay is wired as proposed by SunSynk.

Many Installers chose not to install an RCD upstream of the Inverter and some use the Grid Feed to control the Earth-Neutral-Bond Relay with N/C contacts. The latter workaround will leave you with a floating Neutral from the moment the Grid comes back ON until the Inverter actually switch back to the Grid. (60sec - 2 minutes)This is already an indication that the ATS240V Signal is to late in respect to the Actual Switching back to the Grid.

Inverter Firmware version: MCU:3374

Connection;

See attached wiring diagram.

1. Inverter’s “Island Mode” is enabled.

2. There is a permanent Earth-Neutral Bridge at the GRID side at the closest Mini Sub/Distribution Board.

3. Earth-Neutral Bond Relay connected to the ATS240V signal. N/O contacts connected to Neutral and Earth.

4. Non Essentials Loads get their power after the Grid’s 63A MCD with their own 32A MCB and 30mA RCD.

5. The Inverter Grid connection has its own 40A MCB and 30mA RCD.

6. The Inverter LOAD output feed the Essentials via a 32A MCD and a 30mA RCD.

7. AUX output is not in use. That will only be after solar installation. Nothing connected.

Fault:

1. Switching System ON: All OK and running from the Municipality Grid Supply. Earth-Neutral bridge at Grid Feed.

2. Grid goes down: All OK as Inverter takes over the LOAD. Earth-Neutral bridge via the Earth-Neutral Bond Relay.

3. Grid comes back ON: After ±70seconds the RCD feeding the Inverter trips the moment the Inverter switch back to Grid.

4. Notes on the issue:

· The Grid reconnect time is set to 60sec

· As a test I also switched the Non Essential LOADS and most Essential Loads off.

· Nothing is connected to AUX Output.

· I believe that the RCD trips because the Inverter changed back just before the Earth-Neutral bridge opens (to late ATS240V signal)

· The ATS240V signal must 1st goes LOW, before the actual change back to Grid occurs. It must be at least 30ms before the actual change back happens to compensate for the Earth Bond Relay’s time of response when opening.

· I tested this by manually disconnected the ATS signal just before it goes LOW (around the 60sec mark after Grid down). This will cause a floating Neutral as the Earth-Neutral bridge is then broken. The RCD did not trip with this test as the actual change back is now after the breaking of the Earth-Neutral Bond opened.

· The RCD is a Type AC as I could not find a Type A at the time; however I don't think that it is the issue, as my test proof that it is not the RCD.

· Note that the ATS240V vs. Changeover timing is fine when the Grid goes down as no trips then.

Suggested solution:

SunSynk to fix this issue:

Change the Firmware to make sure that when the GRID coming back ON, the Earth-Neutral Bond is open before the Inverter switch the LOAD back to Grid. Different Contactors or relays will have different “Time of response when opening”. This must be taking into account when advancing the ATS240V signal versus the actual change back time. A Software Setting where one could advance this timing from 0 to -100ms might help