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Hi,

Almost all generators above, say, 8kVA seem to be three-phase. However, it's very normal for large loads (typically air conditioners) to accept only single phase, especially where the generator is just a backup source for when the mains power is out - the building may have been wired for single-phase grid/mains power in the first place.

In this case, it seems to be normal to wire each large load to one of the three phases, such that when all the loads are switched on, the loading is approximately balanced.

However, it's quite rare to have every single load operating at its capacity at the same time. This means that situations where 80% of the generator rating is being output on phase 1 whilst phase 2 and 3 are (at some instant) completely unloaded.

In this case, current is sent out on phase 1 and returns on the neutral. From my understanding, this seems to have the effect that the neutral point drifts away from being truly neutral, meaning that the phase-to-neutral voltages across all phases are unequal and can fluctuate by huge amounts. This can trigger normally undervoltage (occasionally overvoltage) protection cutouts on the generator.

I sort-of resolved this by adjusting the undervoltage cutout threshold downwards, as well as adjusting a related time, to try to reduce the frequency of cutouts.

My questions are:

1) Is my understanding of the reasons for the voltage fluctuations correct?

2) Is severely reducing the under voltage cutout threshold likely to be a problem for the generator or for any appliances?

3) Is there a better way to resolve these issues?

Thank you Anton

Hi,

Almost all generators above, say, 8kVA seem to be three-phase. However, it's very normal for large loads (typically air conditioners) to accept only single phase, especially where the generator is just a backup source for when the mains power is out - the building may have been wired for single-phase grid/mains power in the first place.

In this case, it seems to be normal to wire each large load to one of the three phases, such that when all the loads are switched on, the loading is approximately balanced.

However, it's quite rare to have every single load operating at its capacity at the same time. This means that situations where 80% of the generator rating is being output on phase 1 whilst phase 2 and 3 are (at some instant) completely unloaded.

In this case, I believe that current is sent out on phase 1 and returns on the neutral. From my understanding, this seems to have the effect that the neutral point drifts away from being truly neutral, meaning that the phase-to-neutral voltages across all phases are unequal and can fluctuate by huge amounts. This (or whatever is going on) can trigger normally undervoltage (occasionally overvoltage) protection cutouts on the generator.

I sort-of resolved this by adjusting the undervoltage cutout threshold downwards, as well as adjusting a related time, to try to reduce the frequency of cutouts.

My questions are:

1) Is my understanding of the reasons for the voltage fluctuations correct?

2) Is severely reducing the under voltage cutout threshold likely to be a problem for the generator or for any appliances?

3) Is there a better way to resolve these issues?

Thank you Anton