Quantcast Maintenance of metalclad circuit breakers

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TM 5-684/NAVFAC M O - 2 0 0 / A F J M A 3 2 - 1 0 8 2
tions is approximate, although it may be a useful
measurements, tests, and final checks before insert-
ing the drawout portion into the switchgear cubicle
guide in the absence of other information.
for re-energization as appropriate.
(3) Influence of seuere duty. Contact erosion
b. Air-circuit breaker maintenance requirements.
and damage from severe mechanical stresses may
Remove box barriers from the circuit breaker and
occur during large fault interruption. Reliable indi-
clean all insulating parts including the bushings
cation of the stress, which a circuit breaker is sub-
and the inside of the box barriers. The unit is now
jected to during fault interruptions, can be obtained
ready to be inspected, operated, and tested.
by automatic oscillograph records on systems which
(1) Visual inspections. Inspect the unit to de-
provide this feature. Deterioration of the circuit
termine its operating condition. Perform any re-
breaker is proportional to the energy dissipated in
pairs in accordance with the manufacturer's in-
the circuit breaker during the interruption. The en-
structions.
ergy dissipated is proportional to the current and
(a) Check the bushing primary disconnect
the duration of arcing, that is, the time from the
stubs and finger cluster. Bushing insulation should
moment the contacts part to current interruption.
be clean, dry, smooth, hard, and unmarred.
However, oscillographs do not always record the
(b) Check i nsulation and outside of arc
moment that the contacts part, and it may be nec-
chutes for holes or breaks; small cracks are normal.
essary to determine the parting from indicated re-
If ceramics or fins are broken replace arc chutes.
lay time and the known time for circuit breaker
The throat area of arc chutes may need to be cleared
contacts to part. When automatic oscillograph
of contamination with crocus cloth.
records are available, they may be as useful in guid-
(c) Check arcing and primary contacts for
ing oil circuit breaker maintenance as in showing
uneven wear, or impairment from burns and pit-
relay and system performance. When automatic
ting. Correction of damage by smoothing or resilver-
oscillographs are not available, an approximate in-
ing may be necessary. Replace badly damaged con-
tacts. Follow the same procedure for primary
dication of fault duty imposed on the circuit break-
disconnect stubs and other current-carrying parts.
ers may be obtained from relay targets and accom-
Grease contacts with an approved grease.
panying system conditions. All such data should be
(d) The tightness of all connections is of
tabulated in the circuit breaker maintenance file.
paramount importance. Check and tighten or se-
8-15. Maintenance of metalclad circuit break-
cure, as necessary, any loose nuts, bolts, retaining
ers.
rings, and mechanical linkages which are a part of
the circuit breaker and its operating mechanism.
The insulating media covered include air and
Ensure that all electrical wiring connections are
vacuum.
secure.
a. General maintenance procedures. The follow-
(e) Check all bearings, cams, rollers, latches,
ing suggestions are for use in conjunction with
and buffer blocks for wear. Teflon-coated sleeve
manufacturer's instruction books for the mainte-
bearings do not require lubrication. All other sleeve
nance of drawout medium-voltage circuit breakers
bearings, rollers, and needle bearings should be lu-
installed in metal-clad switchgear. Record all prob-
bricated with SAE 20 or 30 machine oil. Lubrication
lems.
is not required on ground surfaces having a dark
(1) Basic requirements. Drawout devices
molybdenum disulfide coating. Lubricate all other
should be removed for inspection and operation.
ground surfaces such as latches, rollers, or props
During inspection all deposits or dust will be re-
with an approved grease.
moved with a clean lint-free cloth; a vacuum cleaner
( f ) Check actuator relays, the charging mo-
might be helpful. All smoothing of surfaces should
tor, and secondary disconnects for damage, evidence
be done with crocus cloth.
of overheating, or insulation breakdown.
(2) Operating history. Record the number of op-
(g) Check contacts of control relays for wear
erations of the circuit breaker.
and clean as necessary.
(3) Test position. Before complete removal put
(h) Check fo r possible damage to wiring and
the circuit breaker in the test position. Use a test
replace any wiring with worn insulation.
coupler to operate the circuit breaker electrically.
( i ) Check for damage to magnetic blow-out
Check the performance of all controls such as pro-
coils if they are used.
tective relays, switches, motors, indicating devices,
(2) Operations and measurements. After cor-
and alarms.
recting any deficiencies revealed by the visual in-
(4) Remove the drawout portion of the circuit
spection, perform these circuit breaker operations
breaker and perform visual inspections, operations,
and measurements.
8-10





 


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