Phase Sequence of Harmonics

Harmonics of different orders have different phase sequences. What is phase sequence any way? In simple terms, a phase sequence is the order of rotation of phase vectors relative to each other. Positive sequence has a phase order of "abc", a Negative sequence has a phase order of "acb" and a Zero sequence system, the phase vectors has the same phase angles.

Harmonics of different order form the following sequence set:

Positive sequence: 1, 4, 7, 10, 13, ...
Negative sequence: 2, 5, 8, 11, 14, ...
Zero sequence: 3, 6, 9, 12, 15, ...

Zero sequence is also called triplen as it is in the multiples of 3 and this is the current flowing into the neutral of a three phase system.

From Effects of harmonics on Electrical Equipment, a 6-pulse VSD has the following harmonic orders:

5th Harmonic (250 Hz): 20.0% x I1
7th Harmonic (350 Hz): 14.3% x I1
11th Harmonic (550 Hz): 9.1% x I1
13th Harmonic (650 Hz): 7.7% x I1
17th Harmonic (850 Hz): 5.9% x I1
19th Harmonic (950 Hz): 5.3% x I1
23rd Harmonic (1150 Hz): 4.3% x I1
25th Harmonic (1250 Hz): 4.0% x I1
29th Harmonic (1450 Hz): 3.4% x I1
31th Harmonic (1550 Hz): 3.2% x I1, etc

The above table indicates that a 6-pulse VSD theoretically does not produce zero sequence currents.

About the Author

Ver Pangonilo
A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia and Professional Electrical Engineer (PEE) - Philippines with extensive experience in concept select, front-end engineering, HV & LV detail design, construction and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and waste water pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).
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