Harmonic Currents?

[The Iceman]

Can anyone help me better understand Harmonic Currents. For example, an office building with personal computers, fluorescent lighting, and copiers supplied by a three-phase wye service. I understand that these are nonlinear loads, that produce higher frequencies, and results in larger currents on the grounded neutral conductor. This is my basic understanding of Harmonic Currents. Can anyone elaborate on this subject?

 

[brian john]

for starters

http://www.ce-mag.com/99ARG/Martin103.html

http://www.electrical-contractor.net/Need_To_Know/Harmonics.htm

 

[The Iceman]

Alot of people believe that Harmonics caused by nonliear loads will trip GFCI protected circuits, such as fluorescent lights. Sorry about asking another question, but is this true?

 

[iwire]

Even with harmonic currents the current 'out' on the circuit will equal the current 'in' on the circuit.


I think florescent fixtures can trip GFCI protected circuits by current leakage of the secondary side of the ballast and lamps.

 

[Besoeker]

Can anyone help me better understand Harmonic Currents. For example, an office building with personal computers, fluorescent lighting, and copiers supplied by a three-phase wye service. I understand that these are nonlinear loads, that produce higher frequencies, and results in larger currents on the grounded neutral conductor. This is my basic understanding of Harmonic Currents. Can anyone elaborate on this subject?

Many single phase loads take non-linear currents resulting in harmonics. In particular, 3rd and multiples of it (triple-n) are particularly troublesome for the rating of neutrals. This because the third and its multiples are in phase from all three phases of the input supply and add together in the neutral rather than cancelling.
It's maybe easier to see if you draw it out.