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janjan avatar image
janjan asked

3x10kva output dips on grid connect/disconnect

We have 3x 10kva Quattros in a 3phase connection working with a Fronius Symo 8.2-3-M inverter. There are multiple loads (aircons, PC's, wash machines and more) that reset every time a grid failure and grid connection is made (load shedding). We have never seen this before, any help?

VEconfig:

  • UPS function is ticked
  • Low Disconnect was recently changed to 205v and reconnect 208v (as advised by some)
ups
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Alistair Warburton avatar image Alistair Warburton commented ·

What is your system output voltage set to? If you are load shedding I assume you have a poor/limmited grid connection which may be a lower voltage than is typical, especially just before the shedding occurs.

What faults/alarms are you seeing?

Check the AC out voltage imidiatly before and after an event that causs things to reset... You want it set fairly close to your typical grid voltage.

Have a look at the the week AC and dynamic current limit functions as well as 'Accept wide input voltage and frequency'

UPS may well be causing issues rather than helping, it makes the system more fussy about power quality and disturbences.

Can you replicate the issue at will? if so a couple of meters with Min/Max hold functions for both current and frequency may give you some insight.

Lastly make sure it is a vlotage/frequency/current issue and not something else triggering a shutdown like a failed ground relay check.

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janjan avatar image janjan Alistair Warburton commented ·
Hi Alistair, Thank you very much for your reply.


AC out voltage before and after power make/brake is the same. We disabled UPS, without luck. This site is quite remote so it is not easy to fault find the issue, thus the delay in my reply.

I think it has something to do with an inductive load that we are not aware of that pulls a lot of amps when the inverter make/brake contact with the grid (we noticed a few overload alarms as well recently).

What I do find storage is that when the inverter overloads then it is not possible to reset the inverter with the cerbo control unit. It display freezes on "resetting" but we have to switch off the battery power to force the inverter to reset. I've updated all firmware without luck. I am going to create a new question on this.

Once again thanks for your input!

JJ




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janjan avatar image janjan commented ·

This is a new installation and latest firmware v497 is loaded.

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1 Answer
janjan avatar image
janjan answered ·

Hi,

I've disabled UPS and Enabled "Accept wide Frequency" on veconfig to see if I can get a smooth transition from the grid to inverter on the loads.

The Following issues were then detected.

  • The power grid went dead last night we saw these very strange frequency spikes on the output of the inverter AFTER the grid came back on. There were no frequency spikes from the grid at that stage. The inverters also switched off each time for a few seconds during this period.

More clearly in this video (please let me know if you can't see it):Click here to see video: https://www.loom.com/share/4a377510dec14806acbeacc63988c609


  • The transition time when the grid goes down and also when the grid comes back on is about 2 seconds. All the appliances switch off and back on each time this happens.


  • The inverters do not reset themselves if there is an overload detected on the output (suppose to reset 3times, then stay off). A hard reset is required by disconnecting all the batteries and restarting the inverters that way. (Note that "Do not restart after short-circuit VDE 2510-2" is NOT ticked). We replaced the cerbo, and the issue was not fixed.


  • No alarms are detected on the VRM portal for any of the above. It looks like the site is working 100% according to VRM.

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