G5/4 regulations and generators

[jpcqub]

I’ve a few questions here!
Do the new G5/4 requirements apply to generators? Different companies can perform calculations to inform you what size and type of filter you require for your plant to be G5/4 compliant but sometimes these calculations do not take into account the situation when the plant is run by the generator. How does this change the calculations and what effect do the harmonics have on the generator? I’ve heard they (harmonics) are a problem for the generator’s sensing module (AVR ?) but would it not make more sense, if possible, to install a smaller cheaper filter just before the AVR’s input instead of upgrading the main filter to accommodate the generator when its in use?

Thanks.

 

[motorspert]

The G5/$ regulations refer to the harmonics inposed on the system. they are measured (or calculated) at the PCC (point of common coupling) which is usually the site incomer. Within the site, eg on a LV board they can be as high has you like - the responsibilty is then yours to make sure it doesn't cause heating problems with your other equipment.

When the plant is run by a generator (ie in island mode) the harmonics could well be higher as the generator will likey have a lower fault level than the grid. The network operator has no interest in your harmonics in this condition - however your equipment may suffer from the harmonic effects.

Thus, you are probably right to filter locally (AVR)

 

[cflatters]

If you are likely to have harmonics then this shoud be discussed with the alternator manufacturer as this will derate the set.

Increased I^2R losses due to harmonics present in waveform, added to this the harmonic waveform distortion in the generator will probably be around 2% even on a resistive load.

Speak to an alternator specialist.

If you can use active filtration to eliminate the harmonics at source then great, this will certainly help.

 

[ozmosis]

No, unless your generator is generating back into the public supply. G5/4 is soley responsible for the effects of non-linear loads back into the public network.
Of course, you need to make sure your harmonic levels are acceptable for your own 'back-yard' but this is not an actual requirment of G5/4.
If you have a stand-by generator then be wary of the effect of any harmonic mitigation you may include on the supply(main) based on certain impedance levels, fault levels etc. If you then switch in your back-up generator that will likely have a lot higher impedance, then this could really screw up any localised mitigation systems.