Inverter

[RegElec]

Hello to all.
I need some advice from the people who know how the internal circuits work on the hybrid inverters. Mine is a 3KVA 24V with a built in charger and solar panel input (none currently connected).

With the Eskom supply on, the socket outlets fed from the sub DB (inverter supplied) are working correctly. The earth leakage tester trips out the unit in the sub DB (Q3). However, if the Eskom supply fails (Q1 main DB off) and the circuit is then supplied from the battery / inverter then the earth leakage (Q3) does not trip.

The EV with Eskom on is 0.15V and when the Eskom power is off and the sub DB is running on the inverter the EV is 45V.

I have measured between the 'raw' neutral at the main DB and the neutrals at the changeover switch on position I and II. Pos I - virtually zero. Pos II - 45V.

[GCE]

You need to fit a relay/contactor to bridge neutral and earth on the output of the inverter when mains fails

When mains comes back on the bridge between neutral and earth needs to disconnect

[Isetech]

It looks like you are missing the neutral/earth bridge on the inverter output (UPS)


Measured at the inverter UPS output in islanding mode (these are generally the readings you will see of the neutral/earth bridge is not fitted.)

L-N = 230 VAC
L-E =80 VAC
N-E = 125 VAC

[Isetech]

the "changeover" switch in the drawing is not a changeover switch, it is a bypass switch used to isolate the inverter in case you need to work on the inverter.

I would modify the drawing and fit a double pole geyser type mcb for the bypass switch and a double pole geyser combo type ( I find it is way cheaper top use a double pole isolator) for the inverter input.

The way your drawing is wired at the moment, would result in your bypass switch serving no purpose if the inverter is removed for what ever reason.

[RegElec]

the "changeover" switch in the drawing is not a changeover switch, it is a bypass switch used to isolate the inverter in case you need to work on the inverter.

I would modify the drawing and fit a double pole geyser type mcb for the bypass switch and a double pole geyser combo type ( I find it is way cheaper top use a double pole isolator) for the inverter input.

The way your drawing is wired at the moment, would result in your bypass switch serving no purpose if the inverter is removed for what ever reason.

Should the inverter fail the switch can be moved to position I and the circuit will be fed from Eskom mains only.

[RegElec]

You need to fit a relay/contactor to bridge neutral and earth on the output of the inverter when mains fails

When mains comes back on the bridge between neutral and earth needs to disconnect

Is there any reason why the inverter manufacturers don't include this in their circuitry? Even if the supply is not fed from TN-S then the software could be set to disable the internal relay.

[Isetech]

How do you isolate and disconnect the inverter without interfering with the grid bypass?

Should the inverter fail the switch can be moved to position I and the circuit will be fed from Eskom mains only.

[Isetech]

Some of the better quality inverter do have built in relays and/or terminals to control a relay.

No SABS, no control.

You must have an axpert type inverter. (meccer,RCT,MCE, etc etc) there are lots of rebranded units.

[RegElec]

You need to fit a relay/contactor to bridge neutral and earth on the output of the inverter when mains fails

When mains comes back on the bridge between neutral and earth needs to disconnect

So something like this then:

[Isetech]

Your drawing is incorrect.

Just a quick tip, if you decide to use a relay, makes sure the switch over from grid to islanding and back is instantaneous and relay functions at the same time.

If there is a delay switching back to mains, make sure you link the relay coil to the contact or source that controls the switch over.