help plz neutral harmonics

[aandth]

I monitored a commercial building for one week and the harmonics (neutral) result as:
THDv(N)=31.2% && 3rd harmonic=21.89%
THDi (N)= 194.4% && 3rd harmonic= 186.8%

could anyone tell me what are they mean and how to mitigate them..

thanks

 

[Skogsgurra]

That means that the third harmonics combine in the neutral. It also means that you have lots of computers or other non-linear loads connected from L to N.

The percentage is not a problem. The question is how many amps you measure in the neutral. Of course, if you got 32% THDv, it doesn't look good.

Gunnar Englund

http://www.gke.org

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

 

[aandth]

thanks alot
the maximum amps in neutral is about 150A at rush work hour

 

[Skogsgurra]

Does the neutral run hot?

Gunnar Englund

http://www.gke.org

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

 

[sibeen]

As Skogs is alluding to, what matters is the size of the cable. If you've got 150A running in a 16mm cable then you've got a problem. If the same current is running in a 70mm cable, then it is not an issue; with the caveat that as long as your voltage harmonics on the phase voltages are not excessive.