Quantcast Chapter 13. Power Capacitors

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
13-1. Description of power capacitors.
vided for power-factor improvement. The benefits of
improved voltage level, released system capacity,
Power capacitors for use on electrical distribution
reduced system losses, and the reduction in the
systems provide a static source of leading reactive
power bill all stem from the improvement in power
current. Power capacitors normally consist of alumi-
num foil, paper, or film-insulated cells immersed in
a biodegradable insulating fluid and sealed in a
13-3. Application of power capacitors.
metallic container. Depending on size and rating,
Shunt capacitors are used on distribution circuits to
they are available as either single- or three-phase
reduce the kilovoltampere load on a low power fac-
units. Power capacitors are rated for a fundamental
tor circuit. Fixed shunt capacitors are used to im-
frequency, voltage, and kilovar (kilovoltamperes-
prove the voltage level and switched shunt capaci-
reactive) capacity and are generally available in
tors are used to improve voltage regulation.
voltage ratings up to 34,500 volts and 200 kilovar.
Capacitor installations will generally be connected
Individual units may be connected in series and
grounded wye because of undesirable effects of
multiples to provide banks of various capacities and
other connections. All capacitor banks should be
voltage ratings.
equipped with a means to disconnect them from the
13-2. Types of power capacitors.
electric system. Some systems utilize ungrounded
connections to minimize interference and because
The terms "series capacitor" and "shunt capacitor"
this connection is considered easy to fuse.
are used to identify the type of connection and do
not indicate a difference in the power capacitor con-
13-4. Permissible power capacitor dielectrics.
a. Series power capacitors. Series power capaci-
Capacitors containing polychlorinated biphenyl
tors are primarily used for voltage regulation and
(PCB) should have been disposed of under the pro-
receive very limited application in electrical distri-
cedures of the Environmental Protection Agency to
bution systems. In the usual application for power
implement the Toxic Substances Control Act of
service, the series-capacitor kilovar rating is too low
1976. If not disposed of, they should have been
to improve the power factor significantly.
marked as containing PCB's. ANSI/IEEE 18 now
b. Shunt power capacitors. The shunt power ca-
requires an impregnant identification visible from
pacitor is a capacitive reactance in shunt with the
the ground with a glue color used to designate a
electrical load or system and is fundamentally pro-
nonPCB liquid.
13-5. Ensuring safe capacitor deenergizing.
of light load on the circuit. In addition to visual
observations, this inspection should include voltage
Capacitors retain a charge after they are deener-
and current readings to ensure that voltages and
gized. After capacitors are deenergized allow at
currents do not exceed capacitor rating limits. Op-
least 5 minutes for discharge and then short the
erating kilovars (the sum of the fundamental fre-
capacitor terminals to ground and to each other.
quency kilovars and any harmonic frequency
These grounding provisions should remain until
kilovars) should not exceed 135 percent of the ca-
work on the installation is completed. Although
pacitor rating. Routine maintenance and inspection
most power capacitors have a discharge resistor in-
should be accomplished at least four times per year.
stalled to automatically discharge them after they
are disconnected from the circuit, it is not advisable
13-7. Ventilation of power capacitors.
to depend entirely on such resistors for safety.
Power capacitors are very efficient but do generate
13-6. Power capacitor inspection schedule.
some heat which must be adequately ventilated.
The initial inspection should be made within 24
Make sure that airflow around the individual ca-
hours after energizing a new capacitor installation.
pacitor units is not obstructed. Be especially careful
This inspection should be made at a time of maxi-
in checking vertical capacitor banks, where heated
mum circuit voltage, usually during the first period
air around the lower units rises to the top rows.


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