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exportenergy asked

Anomalies on the output frequency with Quattro inverters

Good day, we have a 90kW 3 phase system using 6 X 15KVA Quattro's. Last week we had a ESKOM supply issue as one of the fuses blew on the L2. The system immediately showed that the grid was lost but we noticed that the output frequency was up and down. (50-53Hz) This of course stopped the Fronius inverters as they gave an error - Input Frequency to High.

We solved this by switching the ESKOM breaker off until they replaced the fuse.


Question is how come the inverters did not regulate the frequency to 50Hz. Below the output frequency until we switched the breaker off just before 7AM.

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MultiPlus Quattro Inverter Chargerfrequency
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JohnC answered ·

@ExportEnergy

Grid frequency can't be changed, only by the supplier. And in this case they appear to have lost control. The fuse likely a victim rather than the cause. Nothing you can do except isolate from the grid.

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exportenergy answered ·

@JohnC , yes I do understand and agree with you about the grid frequency.


question is still why the inverters did not open its internal relay and to output only the 50Hz frequency as it should when inverting.

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JohnC avatar image JohnC ♦ commented ·
@ExportEnergy

The range Quattro will reject at is quite wide. I think it's +/- 5Hz as standard, but can be widened even further. Hz within this range isn't normally considered an issue, and even AC coupled inverters are controlled with a deliberately raised Hz. Your Fronius within closer limits.

Gensets can be a problem too. I've a custom widget for mine with the page scale set at +/- 3Hz and it occasionally spikes off the page.

It's the mechanical device at the other end of the ACIn cable that's the weakness. Mostly people overlook it, and many never look at it.

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