Quantcast Maintenance of low-voltage power circuit breakers

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
(2) Clean insulating parts, including bushings.
values. Also check alignment and contacts of pri-
mary disconnecting devices for abnormal wear or
(3) Check the alignment and condition of the
damage. Check for sulfide deposits and use a sol-
movable and stationary contacts, and adjust accord-
vent, such as alcohol, for removal of these deposits.
ing to the manufacturer's instruction book.
(e) After cleaning and adjusting, run insula-
(4) Check arc chutes and replace any damaged
tion resistance tests to measure resistance to
ground and compare with previous readings for any
(5) Inspect the circuit breaker operating
sign of weakening of the insulation system. Com-
mechanism for loose hardware and missing or bro-
parisons should be made using a common tempera-
ken cotter pins. Examine the cam, latch, and roller
ture and humidity base.
surfaces for damage or wear.
(3) Miscellaneous checks. Check supporting de-
(6) Clean and lubricate the operating mecha-
vices such as protective relays and controls as cov-
nism with a light machine oil (SAE-20 or SAE-30)
ered in chapter 11 and as follows:
for pins and bearings. A nonhardening grease
(a) Test key interlock systems by a key ex-
should be used for the wearing surfaces of cams,
change made with devices operating in an off-
rollers, and other operating parts.
normal position to ensure that they have not been
(7) Set the circuit breaker's operating mecha-
bypassed. A closure attempt is required on locked-
nism adjustment, as described in the manufactur-
open devices and an opening attempt is required on
er's instruction book. Excessive wear and the need
locked-closed devices.
for a complete overhaul is usually indicated when
(b) Finally, c ompare equipment nameplate
these adjustments cannot be made within the speci-
information with latest one-line diagram and report
fied tolerances.
(8) Replace contacts, if badly worn or burned,
8-16. Maintenance of low-voltage power cir-
and check the control device for freedom of opera-
cuit breakers.
(9) Inspect wiring connections for tightness.
The following guidelines are provided for mainte-
b. Switchgear. Follow the appropriate recommen-
nance of low- voltage circuit breakers. Also follow
dation for medium-voltage switchgear.
the manufacturer's detailed instruction.
a. Maintenance.  Maintenance is given for
8-17. Repair of circuit breakers.
drawout circuit breakers. Modify instructions, as
Table 8-1 is a troubleshooting chart for the oil por-
required, if circuit breakers are of the fixed type.
tion of medium- and high-voltage oil-insulated cir-
(1) Initially check that the circuit breaker is in
cuit breakers. Table 8-2 is a troubleshooting chart
the test position, prior to withdrawing it from its
for medium- and low-voltage power circuit breakers.
Table 8-l. Troubleshooting chart for oil problems
Locate point of leakage and repair. Tighten
Leakage of oil. Oil throw during opera-
Insufficient oil (in oil-circuit-breaker
up joints in oil lines. Fill oil tanks to
proper oil level.
Drain poor oil, and filter or replace with
Carbonization from many operations.
Dirty oil (in oil-circuit-breaker tanks).
new oil. Clean inside of tank and all inter-
nal parts of breaker.
(1) Condensation of moist atmosphere.
(1) Drain and filter oil or put in new oil.
Moisture present in oil.
(2) Repair source of water entrance.
(2) Entrance of water from rain or other
Filter or put in new oil. Remove source of
Sludging of oil.
Put in new gaskets, treated in accordance
Improper installation of gaskets at a pre-
Gaskets leaking.
with circuit breaker instruction book.
vious inspection or repair. Oil saturation.
Thoroughly clean all insulated parts. Bake
Absorption of moisture and accumulation
Insulation failure.
or dry out water-soaked parts (or treat in
of dirt, grime, carbon and the like on
accordance with directions in the circuit
bushing and insulating parts.
breaker instruction book).


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