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If you have a facility (school, hospital, wastewater treatment, etc), that has a generator as a backup power source for when utility power goes out, what level of harmonics is acceptable within that facility while on gen power?
Suppose you said to follow the IEEE 519 standard for that gen power scenario. I’d ask, what requirement does IEEE 519 offer for this scenario? IEEE 519-2022 clarified Table 2 note C, indicating the 5% TDD target, was intended for power generation FACILITIES – and NOT power generation EQUIPMENT (like a back-up gen).
The back-up gen at my local hospital does not feed back to the utility, it only feeds that building – thus that hospital is not a power generation facility. During gen power mode, there is no Point of Common Coupling (PCC) back to the utility, thus no IEEE 519 applicable standard to follow. In other words, I’m saying the numerical requirements of IEEE 519 don’t apply to this scenario.
So, if the answer isn’t IEEE 519, what is the answer? Remember the “Weakest Link” TV show? That’s your answer. Find the weakest link. What do I mean by this? A system designer must identify what level of voltage distortion (THDv) is appropriate for the FACILITY during that short-term condition, and also determine what THDv the GENERATOR can handle. Whichever of those two numbers is smaller is your weakest link. Then, do a harmonic analysis with gen power, and design the system to keep the THDv at or below the weakest link value.
There is more to the system design topic, as there are multiple variables that impact each other, such as how the size of the generator impacts the THDv or how to determine the weakest link. Check out the tech note below if you are interested in learning more about harmonics on back-up generators and/or IEEE 519-2022.
When I’m asked, what are some of the more meaningful differences between IEEE 519-2014 vs 2022, this Table 2 note C update/clarification is an important one for system designers/consulting engineers to appreciate.
You can read more in this Tech Note.
