synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
Triplen harmonic currents (3rd, 9th, 15th, etc.) on 3-phase line conductors that are all in-phase with each other are zero sequence waveforms. Therefore to be present they would need a neutral conductor as a return to allow such currents to flow in a complete circuit. Since VFDs do not have a neutral input (except possibly some MV ones) they will not draw harmonic currents at triplen frequencies.
I think the main issue is with L-N nonlinear loads such as rectifiers (in computers, LED lighting, etc.) which draw current in short pulses at the voltage peaks. As was mentioned in at least one previous post, in the worst case the mean-square currents from each phase can add on the neutral so that the total RMS current is 1.732 higher than the phase current (assuming balanced currents).
I think the main issue is with L-N nonlinear loads such as rectifiers (in computers, LED lighting, etc.) which draw current in short pulses at the voltage peaks. As was mentioned in at least one previous post, in the worst case the mean-square currents from each phase can add on the neutral so that the total RMS current is 1.732 higher than the phase current (assuming balanced currents).