
194 14 ◊ Power Factor and Harmonics
The harmonics do not all have the same phase sequence as the fun-
damental. For a three-phase set of 120° square waves with positive
phase sequence, the harmonics alternate in phase sequence –5th, +7th,
–11th, +13, and so on. Single-phase components in a three-phase sys-
tem may arise from unbalances, and these lead to triplen harmonics
with zero phase sequence.
Isolation transformers are often considered a panacea for harmonic
problems. Such transformers do add some reactance that will reduce
the high-order harmonics, but they have no other value except for sup-
pressing zero sequence currents and electrostatic couplings. ...