question

ewalderasmus avatar image

Random grid tripping, but ACin 1 Voltage still present...

Hi all


I have a very odd issue which has happened maybe 2 or 3 times in the last 4 months, today was the last.

What it looks like is the grid falls away for 0.15-0.3 seconds, when I review the data I can see the current going to zero but not the voltage. See the image below.

I can only assume the system is acting as it should, and that either the dip is just too small/ too quick to be picked up by the Quattro's monitoring, or the voltage sensitivity is set too high. South Africa is known for many things, one of them being an unreliable network, so I wouldn't be surprised if it was a voltage dip.


So I guess first and foremost has anyone else experienced anything similar?

And secondly, is there any way to verify exactly why the system started inverting?/ to what extent did the voltage dip?

Regards

Ewald

ESSmonitoringinput current
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@EwaldErasmus

Sometimes downloading the .csv data and looking at it in excel helps. If you have 1 minute monitoring on the resolution on you have a better chance of catching the reason loggin in the data anyway. In Zim we have similar issues, often frequency is the culprit.

It also depends on how tight the voltage tolerances are set on the Victron.

Hi @Alexandra


Thank you that was a good suggestion.


I had a look but that only made me more confused. The grid alarm status seems to have not changed.

Any ideas?


Regards Ewald

1596781758460.png (31.3 KiB)

Is this with ESS assistant programmed?

And what is the htz / frequency

HI @Alexandra


I dont have an ESS assistant programmed. I am using the unit as a UPS and a change over switch, in future I will implement more of a ESS.


There is no change in the frequency at all.

Hi @EwaldErasmus

Then am i correct in assuming virtual switch is active then? If so then this programming will determine when to connect and disconnect.

Is the SA grid code programmed in? Impedence on the incoming AC wiring can also cause issues. So check the incoming cabes are to size. You may find undersizing is the issue as i see it happened after a larger load.

Hi @Alexandra


I dont have any virtual switches enabled.

The events have happened during relatively low loads so incorrect cable sizing can be disregarded in my opinion, but I will definitely keep an eye on it.

2 Answers
marekp avatar image
marekp answered ·

I asked similar question in this post.

https://community.victronenergy.com/questions/61990/system-monitoring-and-event-log.html

The conclusion is, that the hardware is faster than the software.

Inverter reacts to fast and short voltage drop, but soft is not fast enough to register and report it.

I performed little experiment.

Short AC grid failure:

There is no voltage drop but current drops.

Longer grid failure:

Voltage and current drops.


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Hi @MarekP


This is very interesting, and thank you for your testing.

How long was your short grid failure? And is the event picked up in the csv? or does it show similar results to what my CSV showed ?


regards Ewald

Hello, @EwaldErasmus

I have constant problems on phase 3 of my grid.

Short dips of voltage happen couple times a day.

The one on 22. of September, as most of them, was less than a second long.

I know that because my other testing system caches dips longer than a second.

That dip triggered MultiPlus because went below 200V which is set in the grid setup.

CSV file for this and the longer dip is below.

I eliminated irrelevant data.

On the time stamps 8:29:40 and 8:29:41 you can see dips on voltage (214.2V).

The trigger happen between them. :)

The inverting takes longer, after the trigger, probably because MultiPlus has the minimum switchover time or some kind of hysteresis.

The longer drop of the grid, was my doing with the braker on the MultiPlus AC input and it lasted around 30 seconds.

Regards, Marek

Jaco Reinecke avatar image
Jaco Reinecke answered ·

I have seen this in SA. What we deduced is that it happens with LOM when inverter tries to check if the mains is still there.

https://www.victronenergy.com/live/ve.bus:grid-codes-and-loss-of-mains-detection

We have reduced it to two checks left:
1) Check the pre-paid meter, if it is a i.e. a Conlog, it may be an issue.
2) Distance from the transformer in the street. We suspect AC Ripples due to distance, enduced when big loads on same feed goes on/off, thereby affecting the inverter when it tries to check for LOM.


Edit: To mitigate it a wee bit, we are using UK Grid Code.
It was suggested to use Other, but we did not have the guts to test that.

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Hi @Jaco Reinecke


Thank you for this, I deduce the same thing, I have an impedo Vectograph which I should Ideally install which will be able to give me the exact voltage and current waveforms at this time, but haven't had the time to install it.


Currently, I am using None, as I dont have any back feed and my setup is purely as a UPS. It was recommended that we lower the disconnect voltage to help with this, but then we get caught in a catch 22. As lowering the setpoint means that when the load shedding starts your system starts from a lower point, as described by Daniel in the below post.

https://community.victronenergy.com/answers/61739/view.html


I didn't suspect it is a prepaid meter or transformer issue, as the times don't correlate to anything which would indicate this. Its a residential area but has mostly business (over 80%), and I have had this situation happening at 6:40 AM and other random times including weekends when not many businesses are open or fully staffed.

At the moment I have accepted that it will happen and it doesn't bother me too much just wish I could view the trigger of the event so I can for sure know the cause.

Regards

Ewald


Here is another anomaly we picked up.

On a MPII UPS which refused to stay on once Eskom was switched on, it switched off the moment it saw Eskom, and after a week of searching on the AC side for a issue by 3 electricians (they have not tested the earth from the street to the house), we tried SA Grid Code on this UPS ... MPII has been working flawlessly since then.