B
Appendix
EPQ DataNode Series User’s Guide
B-21
Additional Notes on Harmonics
Harmonics, Interharmonics, and DC Offset
Many nonlinear devices, such as those listed in Table 2, inject currents at harmonic (integer multiples of the fundamen-
tal) frequencies into the system. Harmonic currents, and the voltage distortion they create as they flow through system
impedances, can reduce equipment operating reliability and service life.
Table 2 Harmonic Producing Devices
Harmonics are particularly troublesome where capacitors are applied on the distribution system or in customer facilities.
As illustrated in Figure B.7 below, capacitors may force the system into resonance at a harmonic frequency, leading to
high harmonic voltages and currents throughout the system.
Figure B.7 Parallel Resonance
Electronic Power Converters
•
Adjustable speed motor drives
•
Switching power supplies (computers & other office equipment)
•
Fluorescent lighting with electronic ballasts
•
Battery chargers
Arcing devices
•
Arc furnaces
•
Fluorescent lighting with magnetic ballasts
•
Sodium vapor & mercury vapor lighting
Ferromagnetic devices
•
Transformers
•
Motors & generators
When, from the perspective of a harmonic source, a capacitor appears to be in parallel
with the system source reactance, the impedance seen by the source becomes very high
at harmonic number h
p
, resulting in high voltage and circulating current magnitudes at
that frequency.
Harmonic Number
Z
h
p
No capacitor
h
Xc
Xs
MVAsc
MVARcap
p
=
=
X
sc
X
c
Harmonic
Source
System
Voltage
Source
