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hanyhc avatar image
hanyhc asked

Multiplus 2 Output Voltage

Hello

I have 3 Multiplus 2 inverters with 3 phase connection. The problem is that the AC output voltage of one of the inverters has reached a value of 300V and reached 190V on another one ( the output voltage is set to be 230V)

This problem caused great damaged to the clients electrical equipment.

The problem only occurs when Grid power is ON. I tried disconnecting the grid and everything went back to normal.

I tested the AC input voltage and it has a value of 230V so the input power could not be the problem cause.

Tgere is nothing wrong with the inverter connections.

What might be the problem?

Multiplus-IIvoltage3 phase
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klim8skeptic avatar image klim8skeptic ♦ commented ·
A couple of thoughts.


A multi in inverter mode wont go to 300vac.

A multi wont pass through 300vac, or 190vac from the mains for more than a few ac cycles.

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hanyhc avatar image hanyhc klim8skeptic ♦ commented ·

the AC input voltage is acceptable it is not the problem, the problem is the output voltage of the inverter.

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shaneyake avatar image shaneyake hanyhc commented ·

AC input and AC output voltages can not be different when the inverter is grid-tied only in inverting mode.

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3 Answers
Alexandra avatar image
Alexandra answered ·

@Hanyhc

If it is correct in inverting mode then the problem is on the grid side.

Most likely it has lost its neutral reference.

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shaneyake avatar image shaneyake commented ·
Sounds like a wiring problem to me too.
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hanyhc avatar image hanyhc shaneyake commented ·

The wiring is proper and the inverters were running normally with no problem for 6 months, the client decided to change the DC cables, we turned off the system and changed the DC cables. When we turned the system back on the configuration was gone so had to do the configuration all over again.

After that the inverters had the output voltage problem occurred the inverters started making a heavy noise and the voltage of one of them reached 300V and 190V on another one only when the Grid connection is ON.

Note that no modification was made to the AC wiring, and I tested the AC input voltage it was 230V.

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Alexandra avatar image Alexandra ♦ hanyhc commented ·

@Hanyhc

Not necessarily a problem with your setup. I am referring to a problem from the grid side. If it is fine inverting then the problem happens when syncronises to grid. There is an issue with the neutral reference that side. There is a floating neutral.

Measure live to neutral on all phases grid side and see. Is the system still Y connected?

It is very weird that you had to reprogram your units as well, we have had a system not connected to grid or batteries for over 6 months, just on storage. When we connected it up it fired up as before ready to go. So unless the system was updated I dont see how that would have happened.

Do you have a gx device in the system?

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hanyhc avatar image hanyhc Alexandra ♦ commented ·
Yes I have a Cerbo GX. I measured live to neutral on grid side on all phases the voltage was 230 V. Is it possible that disconnecting the batteries led to an internal malfunction?
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Alexandra avatar image Alexandra ♦ hanyhc commented ·

The system was disturbed by the dc rewiring.

Something unexpected is loose or has been i know this is an ac problem, but covers come off and things are changed.

Even in the industrial machinery side we see 300v when the neutral reference is lost in a y setup.

If you check out the multi video, you will see the design sets up the voltage.

It really has to be wiring based. Maybe go over and check all the connections in the entire system are right. Even downstream. Ot is also possible someone in the building has messed up some wiring.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ hanyhc commented ·
You have to check all AC connections. It is possible that you can measure the correct voltage with no loads but a bad connection only makes problems under load.
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mike90 avatar image
mike90 answered ·

We had a similar issue on a different brand of inverter. Ended up being the internal relay not connecting input and output neutral when grid connected, which caused a floating neutral.

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basil katakuzinos avatar image
basil katakuzinos answered ·

Okay a few things come to mind.

1) Check continuity between input and output neutrals when the system is grid tied. (They should be connected within the inverter)

2) Check all voltages phase to phase and phase to ground on the input and output side. There is really no way that the inverter would be outputting a different voltage that what is coming in to the inverter (By design the inverter has to be perfectly synchronised to the grids incoming sine wave), dont check voltages with a cerbo, measure them manually.

From this we can deduce the following

If their is no neutral continuity across the inverter then the problem is with your inverters.

If the voltages on the input side and output side of an inverter are different (Phase to Phase and Phase to ground) then somehow, unexplanably it is your inverter. Though in reality by design this just cant happen as the input and output are basically tied together internally when on grid.

If any of the input voltages are wrong (Phase to Phase and Phase to ground) then you have a problem upstream (Perhaps in a breaker board before the inverter or in the grounding at the utility side, generally within their substation).

As many have said above it is most definetly a floating neutral as this would mean the Phase to Phase voltages will not vary by much but the phases will loose their ground reference meaning that they will eaither have a high Phase-Neutral or low Phase-Neutral voltage.


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