In power systems, there are rules and regulations stating what levels of harmonic distortion is acceptable. One example I've seen for voltage distortion is: THD < 8%, single component harmonic <5%. These values are (hopefully) not random numbers.
From Schneider Electric:
Harmonics are unwanted currents that overload wiring and transformers, creating heat and, in extreme cases, fire. These currents are harmful to equipment. They weaken the reliability and shorten the life expectancy of equipment exposed to the distortion
For induction machines, negative sequence harmonic currents will also cause a negative torque, which of course isn't good.
My question is: How bad is it, really? What can the consequences be if the total harmonic voltage distortion is 10% instead of 8%, if the 7th harmonic is 6% or if the negative 5th harmonic current is 10%. The reason why I ask is: Reducing harmonics does not come for free, is it really worth it in all cases? I know I have to adhere to the regulations, but assuming there were no regulations, what then?
Does anyone have any experience in this area?
I forgot to mention the following in the question: The system I'm studying is not connected to the main grid. It has its own generators, UPS-system and all other necessary infrastructure. The operator and the owner of the system is the same company. The specific regulations I'm mentioning are for such isolated systems, not systems connected to the main grid (could for instance be a vessel).
If you have your own power grid, and all the equipment is your own (thus you would need to take all the costs of installation, maintenance etc), then why are there limits and not guidelines when it comes to harmonics? I understand why there are rules regarding for instance short-circuit levels, arc-flash hazard etc. etc. I also understand regulations regarding voltage drops, as this may lead to motors stalling, loss of excitation and more, I just don't get why there are strict regulations when it comes to harmonics.
How much damage can it do?