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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
within 3 to 4 feet (0.9 to 1.2 meters) of a defective
generated noise such as ignition interference and
insulator or bushing, depending on the severity of
tire static and it should be rugged enough to with-
the interference signal. A good insulator will show
stand the vibration of the truck. The receiver's loud-
no indication at from 6 to 8 inches (153 to 240
speaker must be powerful enough to produce a sig-
millimeters). These distances will vary with line
nal which can be clearly heard above any cab noise.
voltage as well as with the individual lamp used.
a. Self-contained portable equipment. A portable
16-9. Communication interference from elec-
receiver must be used on a section of an electric line
trical lines.
which is inaccessible to the patrol vehicle. The unit
should still be tunable over a wide range of fre-
Loose or corroded insulators and conductor or tap
quencies and should contain its own power supply. A
connections are the major abnormal conditions oc-
portable instrument is also useful in tracing noise
curring in power systems that cause disturbances
on secondary circuits and in facility buildings where
on communication circuits. These insulator or con-
noise may originate.
nection conditions cause high-voltage series type
b. Useful accessory. A small neon lamp, taped to
power arcs on primary feeders. Series-type power
arcs generate a magnetic field which may fluctuate
the end of a hot stick, is a useful accessory to probe
over many miles of circuit. The inductive coupling
for defective insulators and bushings. Use a NE 30
between this field and parallel communication cir-
or 32 lamp with the base and resistor removed. The
cuits results in noise in the communication circuits.
short wires coming out of the glass bulb should be
Power-arc noise on telephone lines can usually be
extended in a manner similar to a television set's
recognized and located by communication workers
dipole antenna rod. Each wire should be about 0.75
trained in this type of work.
inch (19 millimeters) in length. The lamp will glow
Section III-HARMONIC INTERFERENCE
16-10. Harmonic causing devices and their ef-
tion and maintenance responsibilities. This respon-
fects.
sibility includes the facility electrical power distri-
bution systems and required actions to ensure these
Harmonic interference results when excessive non-
systems will supply the standard voltage ranges
linear loads are connected to an electrical system.
given in ANSI C84.1. The electrical supervisor is
a. Use. Nonlinear load producing devices used on
not responsible for the successful and reliable op-
electric power systems include static power convert-
eration of "high tech" electronic equipment, except
ers, arc discharge devices, saturated magnetic de-
in accordance with ANSI C84.1. However, to ensure
vices and, to a lesser degree, rotating machines.
overall proper operation of electrical systems, rec-
Static electric power converters which convert ac to
ommended harmonic distortion limits for voltages
dc, dc to dc, dc to ac, and ac to ac, are the largest
should not be exceeded. Limits are for individual
producers of nonlinear loads. Static power convert-
harmonic distortion and for total harmonic distor-
ers found on military installations are generally
tion (THD). THD is defined by equation. The per-
adjustable speed drives, uninterruptible power sup-
mitted harmonic distortion limits are given in table
plies, or computer work stations.
16-1. These limits are the permissible maximum
b. Effects. The characteristics of nonlinear loads,
harmonic distortion limits for service voltage at the
however, change the sinusoidal nature of the ac
point of common coupling (PCC) with the user or at
power current (and consequently the ac voltage
the building service point.
drop), resulting in the flow of harmonic current into
(Sum of the squares of the rms
the ac power system. This current can damage ca-
magnitudes of all harmonics)"'
pacitor banks, motors, transformers, and loadbreak
THD = [
1 x 100%
devices. Protective relays may malfunction; fuses
(Square of the rms magnitude
may blow erroneously; and inductive interference
of the fundamental)
(eq. 16-1)
may develop in communications circuits. Harmonics
16-12. Electric power quality data.
can significantly increase power losses in distribu-
tion circuits, causing a major increase in
From time to time, harmonic measurements should
unaccounted-for energy and operating costs.
be taken at selected points, where a high level of
harmonic distortion is suspected. Measurements in-
16-11. Electric power quality responsibilities.
dicate the system behavior, and whether harmonics
__
levels are within the limits given in table 16-1.
The facility electrical supervisor (that is the Army
a. Measurements. Instrument response require-
Director of Public Works, Navy Public Works Of-
ficer, or Air Force Base Engineer) is responsible for
ments are covered in IEEE 519. The basic equip-
ment used for harmonic analysis includes:
electrical power quality, as a part of facilities opera-
16-4
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