Quantcast Chapter 16 Electrical Service Interference

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
16-1. Electrical power quality.
bances. The first evidence of this type of interfer-
ence will usually show up as impaired radio or tele-
Electrical end-users are experiencing increased
vision set reception.
problems from the expanding use of disturbance-
producing electrical equipment. Most equipment
16-3. Harmonic interference.
served by electrical facility exterior distribution
lines can tolerate short-term voltage and current
Harmonic interference is produced by nonlinear
variations without operational problems. The con-
loads which draw current discontinuously, or whose
cerns discussed in this chapter are voltage and cur-
impedance varies with the applied voltage.
rent sources which produce excessive and/or con-
a. Sources. Gaseous discharge lamps and solid-
tinuous electrical noise, resulting in unacceptable
state equipment, such as variable frequency drives
electric power quality. These sources may interfere
and computers, are harmonic interference sources.
with adjacent communications equipment or gener-
The accelerated use of solid-state devices has mul-
ate damaging waveforms, which flow back into the
tiplied harmonic input sources operating on resi-
electrical distribution system and extend the inter-
dential, commercial, and industrial electrical sys-
16-2. Electromagnetic interference (EMI).
b. Occurrence. Harmonics can be differentiated
from transients, since harmonics occur as a periodic
EMI occurs when undesirable electrical signals
wave which contains multiples of the fundamental
from an emitting source are transferred, by radi-
ated or conducting media, to a receptor or receiver
60-hertz frequency and transients occur as a tempo-
element. These unwanted electrical signals with
rary variable of the fundamental frequency only.
their undesirable effects are known as electrical
Harmonics have always occurred in power systems
noise (designated simply as noise hereafter). EM1
but increased use of high-level harmonic-producing
includes radio interference (RI) which, as defined by
equipment has made harmonic interference control
the Federal Communications Commission (FCC),
a matter of general concern to both electrical power
includes only 10 kilohertz to 300 gigahertz distur-
distributors and users.
16-4. Electrical distribution system interfer-
16-5. Electrical noise origin.
Noise generated by EMI originates from two
sources: electric distribution power lines and pre-
Electromagnetic interference on a power system is
mises wiring (residential, commercial, or indus-
an avoidable problem. Such interference indicates
trial). Noise is caused by defective installations of
potential line trouble, which may sooner or later
premises utilization equipment and wiring or by
cause an outage on the circuit. Distribution appara-
faulty construction of the exterior electric distribu-
tus and devices have design features which mini-
tion system.
mize electromagnetic interference. Interferences oc-
a. Utilization equipment noise. Utilization equip-
curring on distribution systems result from poor
ment noise can easily be isolated in a building by
quality workmanship or maintenance. Loose con-
disconnecting suspected equipment, item by item,
nections, inadequate grounding and bonding, and
and listening for changes in the noise. These noises
even the location of staples securing the ground
generally result from conducted interference and
wire to the pole are possible sources of EMI. Defec-
will affect consumers connected to a common trans-
tive or improperly adjusted apparatus can add to
former, but do not spread over the system for any
the trouble. Do not wait until a complaint comes in
great distance.
before taking action. Be alert to the problems asso-
ciated with electromagnetic interference, so that
b. Noise originating on electric power lines. Elec-
noise developing on the system can be detected and
tric power line noise can be attributed to three main
eliminated during regular system surveillance. Ad-
causes. The first is defective insulation in some ap-
ditional information on this subject can be found in
paratus part; the second is loose primary or second-
ary connections; and the third is electrostatic leak-


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