TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
switches the interrupter may use some other me-
instructions. Interrupter contacts should be in-
dium, such as sulfur hexifluoride gas. Interrupters
spected for damage caused by arcing. Contacts
should receive the same inspection and mainte-
showing evidence of excessive wear should be re-
nance as the switches on which they are installed.
placed in accordance with manufacturer's recom-
Many interrupter switches are designed so that ma-
mendations. Interrupters with sealed gas-filled
terial is consumed from the walls which are exposed
chambers have pressure gages to indicate loss of
to the electric arc. Particular attention should be
pressure. Field experience indicates that interrupt-
given to such parts, and they should be maintained
ers using a sealed gas chamber will require recharg-
or replaced in accordance with the manufacturer's
ing every 2.5 to 3 years or more often.
Section IV-CIRCUIT BREAKERS
8-12. Circuit breaker usage.
(7) The circuit breaker is grounded.
(8) Suitable b arriers are installed between the
Circuit breakers are a special form of switching
circuit breaker and adjacent apparatus that may be
mechanism, which can open and close circuits under
energized. In crowded installations, barriers may be
both normal and abnormal conditions. When they
of rope or net, with suitable danger flags, or of
are electrically controlled, they can be operated lo-
temporary rigid construction using insulating mate-
cally or remotely, or by both modes. Oil, SF,, gas,
vacuum, and air are the insulating mediums used
(9) Requirements of departmental safety publi-
on most installations. The selection of the insula-
cations are being observed.
tion generally relates to the voltage level being in-
8-13. Frequency of circuit breaker mainte-
a. Voltage level relative to the insulating media
A circuit breaker is a much more complex and ex-
(1) High-voltage units. Until recently most in-
pensive item than the switch and fuse combination,
stalled high-voltage circuit breakers were of the oil-
which fulfills the same function to a lesser degree.
insulated type. However, the use of SF,, gas insu-
Circuit breakers are therefore generally used for
lated units is increasing as SF, units take less space
the more important circuits, where increased reli-
for a given voltage and are environmentally prefer-
ability and flexibility is required for equipment op-
eration and prompt restoration of service.
(2) Medium voltage units. Newly installed
a. Frequency of inspection. The frequency of in-
medium-voltage switchgear utilizes vacuum con-
spection should be based on service and operating
struction which provides a considerable space sav-
condition. A circuit breaker should be inspected
ing over air-magnetic units now being phased out.
whenever it has interrupted current at or near its
In the future, SF, switchgear units will probably
rated capacity. The average frequencies given here
become more common.
should be reconsidered if the following conditions
(3) Low-voltage units. Only air-insulated power
apply or as equipment ages.
circuit breaker switchgear of the solid-state type is
(1) High humidity and high ambient tempera-
described in this manual.
b. Safety measures. Before initiating any mainte-
nance inspection which requires touching a circuit
(2) Dusty or dirty atmosphere
breaker, check to ensure that:
(3) Corrosive atmosphere
(1) The circuit breaker has been tripped (open).
(4) Frequent switching operations
(2) The circuit breaker is disconnected from the
(5) Frequent fault operations
circuit on both sides, either by opening disconnect
b. Maintenance of nonmetalclad medium- and
switches or by removing the drawout portion of the
high-voltage circuit breakers. Most manufacturers
circuit breaker from the switchgear dependent upon
recommend complete inspections, external and in-
ternal, every 6 to 12 months for circuit breakers
(3) All contro1 circuits are open and potentiall
above 15 kilovolts. However, utility company expe-
transformer fuses are removed.
rience has shown that considerable unnecessary ex-
(4) The supply to pneumatically and hydrauli-
pense may be involved in adhering to the manufac-
cally operated circuit breakers is shut off.
turer's recommendations. With proper external
(5) Wound springs in stored-energy mecha-
checks, the expense, delay, and labor of internal
nisms have been released.
inspections may be avoided without sacrificing de-
(6) Circuit breakers and controls are properly
pendability. Internal conditions can be determined
through oil analysis, power factor testing, and the