Quantcast Electrical distribution system interference

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
Table 16-1. Harmonic distortion limits1
ity of resonance between transformer windings and
line capacitance. Increased audible noise may re-
Total harmonic
distortion THD
Bus voltage at PCC
c. Cables. Harmonics result in increased copper
and dielectric losses.
69 kV and below..
Above 69 kV thru 161  1.5..
d. Protective relays. A higher level of harmonics is
generally required to alter relay performance, but a
161 kV and above.. . . .  1.0.. . . . . . . . . . . . .
range of 10 to 20 percent THD may affect relay
operation. In general, high fault currents are not
1993 IEEE. AI1 rights reserved.
severely distorted, since the limiting impedance is
the power system. The harmonic current, which is
significant in relation to load current, will be much
(2) Spectrum analyzers
less significant in relation to fault current. High
(3) Harmonic or wave analyzers
harmonic levels can cause electromechanical relays
(4) Distortion analyzers
to chatter. Distance relays will see an altered im-
(5) Digital h armonic measuring equipment
b. Control of power quality. Maintenance person-
pedance setting. Excessive third harmonics can
cause misoperation of ground relays.
nel are not responsible for controlling power quality
beyond determining, by measurements, whether
e. Instrumentation. Harmonics can lead to erro-
the harmonic distortion of the PCC voltage exceeds
neous positive or negative errors for induction disc
table 16-1. Verify that panelboard loads are bal-
relays, which are normally calibrated for the funda-
anced, where applicable, and check wiring and
mental current and voltage. Distortions of less than
grounds. A majority of power quality problems re-
20 percent THD will not cause significant errors,
sult from loose connections and improper grounding
but in harmonic-rich environments, true rms sens-
techniques, and unbalanced loads. If correcting
ing is needed for accurate measurements.
these deficiencies does not alleviate excessive har-
f. Switchgear The heating effect of the higher
monics, then harmonic mitigation measures must
peak value of a very distorted voltage wave can
be developed utilizing engineering solutions beyond
result in premature failure of the switchgear insu-
the scope of this manual.
lating system. Circuit breakers interrupt current
flow at zero current and a current wave with zeros
16-13. Electrical distribution system interfer-
at locations other than on the fundamental sine
wave can cause circuit breakers to have premature
AIthough harmonic mitigation is not the responsi-
interruption and restrike. Circuit breaker blowout
bility of the electrical supervisor, it is the supervi-
coils can fail to interrupt currents. Loadbreak
sor's responsibility to keep informed on both the
switches, fuses, and other switching devices can be
quantity and quality of electrical service available
subject to the same problems.
to facility users. Therefore, an awareness of appara-
g. Miscellaneous. Equipment not normally part of
tus actions, which may indicate unacceptable har-
exterior electric facilities can be affected by har-
monic levels, is necessary to determine where more
monics in the following ways:
precise data should be acquired.
( 1) Electronic equipment. Electronic equipment
a. Capacitors. Capacitor impedance decreases
is not only a source of harmonic currents, but is
with frequency, and a capacitor bank acts as a har-
prone to misoperation if not operated on its correct
monic sink where most harmonic problems are first
voltage and current waveforms.
noticed. Fuse blowing, without any obvious reason,
(2) Rotating equipment. Rotating machinery
or a capacitor unit failure, can be signs of a possible
will see increased losses, possible reduction in avail-
harmonic problem. A supply system inductance, in
able torque, and (conceivably) mechanical oscilla-
resonance with the capacitor bank, can cause large
tions in prime mover/generator and motor/load com-
currents and voltages to develop. When, for no obvi-
ous reason, all fuses of a capacitor bank blow, it is
(3) Incandescent lamps are the most sensitive to
probably a harmonic problem. If only one fuse
increased heating effect, which can significantly
blows, it is probably a reasonance problem.
shorten lamp Life. Gaseous discharge lighting, such
b. Transformers. Harmonic currents cause in-
as high-intensity discharge and fluorescent lamps,
crease copper and eddy current losses, and har-
can produce harmonics from solid-state ballast com-
monic voltages cause increased iron and dielectric
losses and insulation stress. There can be a possibil-


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