Harmonics
Tips and Hints
10
10-5
Positive sequence harmonics try to make a motor run faster than the fundamental;
negative sequence harmonics try to make the motor run slower than the fundamental. In
both cases the motor looses torque and heats up. Harmonics can also cause transformers
to overheat. Even harmonics disappear if waveforms are symmetrical, i.e. as equally
positive and negative.
Zero sequence current harmonics add in Neutral conductors. This can cause overheating
of these conductors.
Distortion. Current distortion is to be expected in a system with non-linear loads like DC
power supplies. When the current distortion starts to cause voltage distortion (THD) of
more than 5 %, this signals a potential problem.
K-factor: this is an indication of the amount of harmonic currents and can help in
selecting transformers. Use the K-factor along with kVA to select a replacement
transformer to handle non-linear, harmonics-rich loads.
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