Harmonic Currents

[steve66]

I am trying to predict the amount of harmonic currents that will be present on the service to a building. I know the building will have a lot of personal computers, and a lot of electronic ballasts for fluorescent lights.

I know the fluorescent ballasts have less than 10% THD, but I'm not sure about the computers. Also, I'm not sure how much of the 10% THD is in which harmonic. Is most of it in the 3rd harmonic? Or is it more spread out across the higher harmonics.

If anyone has a reference that indicates what the harmoic distrortion vs. frequency is for lights and personal computers, I would appreciate it. For example, maybe something that says standard fluoresenct ballasts have X% at the 3rd harmonic, Y% at the 5th, and so on.

I searched the internet, and haven't been able to find anything.

Thanks:
Steve

 

[brian john]

THD WHAT?

Voltage, Current?

Building voltage 480/277 with SDS 208/120?

 

[jim dungar]

Good luck.

Why are you trying to do this?

THD is almost meaningless, TDD is what is important.
A 1A load with 10% THD has almost no effect on a 100A service.

 

[steve066]

THD WHAT?

Voltage, Current?

Building voltage 480/277 with SDS 208/120?

The software I have has inputs for current distortion, so that's what I need to find. I assume that's also what they mean when they say an electronic ballast has less than 10% THD. There wouldn't be any way to calculate the Voltage THD without knowing how stiff the source is.

The building has a single substation: 4160 to 208/120.

Why are you trying to do this?

Government design specifications.

THD is almost meaningless, TDD is what is important.
A 1A load with 10% THD has almost no effect on a 100A service.

Yes, but the IEEE standard I have to meet has limits for both V(THD) and I(TDD).

I think the intent of the government design spec is to limit the harmonics caused by VFD's. But it also says I need to include all known sources of harmonics. The really hard thing to calculate are the harmonics caused by personal computers and other office type equipment . First I have to guesstimate how many PC's and similar loads there are. And from the scarce info. I've found, up to 80% of a PC's load can be harmonics.

 

[BILLY101]

Check out this info from APC. White paper #26 REV 1 speaks to the Hazards of Harmonics and Neutral Overloads.
Since the paper is copy-writed you need to GOOGLE it.

BILLY

 

[steve066]

Check out this info from APC. White paper #26 REV 1 speaks to the Hazards of Harmonics and Neutral Overloads.
Since the paper is copy-writed you need to GOOGLE it.

BILLY

Thanks. Table 1 is the exact type of info I'm looking for, except it shows the IEC limits. My understanding is that computers sold in the USA are still exempt from any limits on harmonic currents.

I think Table #2 is also helpful, because I think the total K factor or 11.4 can be converted to harmonic distortion. But I'll have to search to see if there is a formula for that. I'm not sure how to do it offhand.

P.S. Is there a restriction on posting a link to copywrited material??

http://www.apcmedia.com/salestools/SADE-5TNQZ5_R1_EN.pdf

 

[jim dungar]

P.S. Is there a restriction on posting a link to copywrited material?

No, but there is a restriction to linking to sites that provide 'free' downloads at the expense of copyright holders.