Extremely Highly Neutral Harmonics

[farmape]

Power logging at the 480V 3P 4W main panel (panel that feeds an outdoor lighting only load)
Consider a three phase 4 wire 480V circuit with the following average amperage (Fundamental) measurements:
L1: 191.5A, -7.84 deg
L2: 177.9A, -130.92 deg
L3: 178A, -253.02 deg
N: 20.6A, -156.9 deg
The actual phase RMS values for the circuit are nearly identical, except for Neutral which is about 65Amps RMS, over 300% higher than the fundamental!
THD values are:
L1: 11%
L2: 11%
L3: 12%
N: 280+%

Any thoughts on these excessive harmonics, is it even possible without some type of outside influence? The 3rd Harmonic is the culprit. Thanks

 

[HamburgerHelper]

Lighting can cause harmonics issues.

 

[dpc]

The HID ballasts can be a rich source of triplen harmonic currents and all phases will add in the neutral, like zero sequence current. Your measurements seem possible since the load is entirely lighting.

 

[farmape]

Thank you, indeed the load is entirely lighting. I guess its at least re-assuring to know that lighting can cause this excessive distortion.
Now I need to reduce them, as they seem to causing ill effects on (another system) control system.

 

[dpc]

Should be straightforward to determine if your other issue does away during the day when the lights are off. My experience has been that most "power quality" problems turn out to be something else. Main problem with the triplen currents I am aware of are transformer overheating and issues on reduced neutrals.

 

[farmape]

Agreed....somehow "dirty power" is always guilty until proven innocent!

 

[Power0020]

That is true for lighting, you need to install electronic ballasts to eliminate these issues.

High neutral current can cause nuisance tripping as well as neutral overheating, extra power loss and flicker as well.

filters will be important in this case

 

[Skogsgurra]

I agree totally with dpc that "most power quality problems turn out to be something else".

I wouldn´t say that 300 % more harmonics than fundamental in the neutral is extreme in any way - just unexpected if you haven't seen it before. As long as the neutral isn't overheated, I think that you should look for the cause of the "ill effects on (another system) control system" elsewhere.

You mentioned that there's nothing but lighting connected to the system. So, if that other system isn't even connected to the panel you are measuring - how could the latter influence the former? A nearby 65 A 180 Hz current is by no means detrimental to a well-designed system. (Don't explain it as "somehow influences")

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

300% on the neutral may be misleading.
If the circuits are well balanced there will be very little fundamental current on the neutral.
Most of the neutral current is harmonic.
If you multiply the phase currents by the %THD, the sum is 62 Amps. That correlates very well with your measured 65 Amps.
You have a little bit of fundamental from a little unbalance and lots of harmonics. 300% of not very much actually.

Bill
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"Why not the best?"
Jimmy Carter