Indication of Harmonic Problems 1

[Nightwolf]

Can someone help me? I need to know if there are any signs to watch for that indicate if you are having harmonic problems especially along the third, fifth, and seventh. Thank you.

 

[infomaniac]

nightwolf, some common problems with 5th harmonic currents is overheating of induction machines (i.e., motors). The 5th harmonic is a negative sequence component and therefore will try to 'reverse' the motor while it is running. This would obviously cause heating effects on the motor.

The seventh harmonic component is opposite. It could actually try to speed up your process because it is a positive sequence component and will add to the positive 60Hz component.

One of the major problems with 3rd harmonics is excessive neutral currents since zero sequence frequencies tend to add in the neutral (i.e., 3rd, 6th, 9th, 12th, etc.). Watch for neutral cable heating with zero sequence components.

Some other problems can inlcude clocks that run fast. We have seen this at several locations. This results due to higher frequencies.

 

[peebee]

Overheating is practically the only problem with harmonics. If you're not overheating, you most likely don't have a problem.

(Okay, power quality may be an issue in some rare installations -- usually the only problem is overheating, though).

 

[redtrumpet]

Cooked capacitors - they sink harmonic currents and so are susceptible to overheating.

 

[GordS]

The harmonic related problems I have faced have also included control related issues - protective devices that respond erratically.

On one case, in a building with 15000 hp of VFD's, we kept getting trips on our 600V system via the undervoltage relay when our harmonic filters tripped.

 

[infomaniac]

redtrumpet, good point. Capacitors can be a very big problem not only from a heating standpoint but also from the effects created from parallel resonance. The amplified current and voltage distortions can be tremendous.

 

[busbar]

One check is to make voltage and current measurements with average-responding and true-rms instruments. Differences indicate a possible problem.

 

[mainepepmp]

Seat of the Pants Method:
Has your electric usage/bill changed significantly?

Seems like I recall an IEEE Power Engineering Society Transactions paper a few years back that also cited measurable effects on analog watthour meters; think it was 5th harmonic, but wouldn't swear to it.

Surf IEEE web site for authors McGranahan, Emanuel, Orr, and/or Cyganski for the best and most direct links to this and other papers like it; can't remember for sure whether any of these people were the authors, as I now I'm thinking the paper might've come out of Georgia Tech (McGranahan = Electrotek & McGraw-Edison; others = WPI).

Elegant Method:
Do it the right way---
Get your Building Services department to arrange for installation of isolation PTs and CTs on your primary and downstream secondary panels, especially those with a lot of solid-state power supplies connected. Buy yourself a harmonics analyzer, plug it in, gather data, and knock yourself out by studying all the data you'll ever need/want and then some, sixty ways to Sunday!

If it ain't smooth, it ain't 60 Hz.

 

[busbar]

Harmonic problems get real subtle on occasion, and may even take alcohol consumption to resolve. My favorite...

http://gashog.net/dat/nonsin.hart01.rtf

Dr Dave Hartmann, BPA retired, received a rousing standing ovation for this one.

 

[GusD]

In addition to causing overheating in electric motors
transformers etc,harmonics may play a part on the bearing life of your electric motors.Harmonics should be minimized or corrected whenever possible.
GusD