Harmonic Analysis

https://en.wikipedia.org/wiki/Harmonics_(electrical_power)

To start with, voltage is supplied by the generator. Current is the load's response to the voltage.

Many loads are non-linear in that they draw current when the voltage is at its peak value. Examples are power supplies which charge internal capacitors and fluorescent lighting which conducts when the gas is ionized. These will cause current harmonics.

Harmonics in the neutral current in three-phase loads will be higher than the phase current harmonics because all three phase currents return through the neutral.

The amount of harmonics present depends on the characteristics of the load and how well it is balanced.

Thanks for the replies,

if the voltage harmonic values are in limits( THD>5 and individual >3),any relevance for current harmonics?

Condensed version of a complex subject.

Current harmonics are what cause voltage harmonics. So the current harmonics in your facility are the source of voltage harmonics, along with the stiffness of the system as measured by the ratio of Available Short Circuit current vs actual Load current. Current harmonics are also affected by EXISTING voltage harmonics in a system in that if there is high V-THD coming in FROM the utility connection, it will make your I-THD worse and the situation can spiral out of control, causing transformers to melt down etc. So V-THD is of concern when you are connected to a utility supply because voltage harmonics travel from you to your neighbors on that common connection. IEEE 519 specifications call out the limitations for the end users AND the utilities with regard to how they affect each other in order to prevent this down hill spiral.

If you are on your own generator, the IEEE 519 rules are irrelevant. They can still be used as a guideline however, because what the I-THD will affect is the capacity or fuel consumption of your generator. The generator has to supply ALL of the power going to the equipment, whether at the fundamental frequency or at the higher harmonic frequencies. If you follow the IEEE-519 guidelines, you can mitigate the impact that harmonics will have on your generator capacity and/or fuel consumption. Or you can chose to ignore it, because it will not affect anyone but you.

what equipment are you running on the gen set power supply?

Motors with VSD's etc?

Thanks for the replies,
want to add one more query:
If i am using a generator supply for the system and my load is sensitive communication system, all i understand is some current harmonics will be there for sure may be higher or lower.
My sensitive communication system is fed by the generator and its having some issues during operation and is it be the only possibility is to provide a UPS supply before the communication system for rectification?.
I also have some utility load in the same bus which is also fed from my generator.

what issues are you having with your generator?

No issues with the generator , but the communication system(Load) having some noise issues.

Noise issues or spikes could be due to your generator not being earthed properly.

Hopefully you have rated the generator to suit your Kva demand, or that will be an issue, also with noise on your comms that could be due to bad connections and equipment earthing.

As I don't know what type of comms you are using, it will be difficult to assess the problems. However i suggest you get the manufacturer to help

Noise is not harmonics...

Common Mode noise is often the result of PWM switching, which often comes from the SAME EQUIPMENT that creates harmonics, so they are often guilty by association. But these are different issues. CM noise is usually made worse by poor grounding practices as mentioned. Start there.