Quantcast Influence of light duty

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
f . Influence of duty imposed. The need for main-
tank, visually inspecting the interior, and wiping
tenance is influenced by any circuit breaker's oper-
down the tank and interior parts.
ating duty. The influence of operating duty given
(a) Maintenance of the integral parts (con-
below for oil circuit breakers will also apply (except
tacts, interrupter assemblies, internal current
for the different insulating medium) to SF, gas-
transformers, resistors, capacitors, and lift rods) in-
insulated circuit breakers.
cludes checking, measuring, adjusting, aligning,
and making repairs as needed. Lubricate all parts
(1) Influence of light duty. If the circuit breaker
and components that are required to be lubricated.
has been energized on both sides, but the contacts
Replace any seals and gaskets, if necessary. Replace
are open, erosion in the form of irregular grooves
all desiccant materials, if applicable.
(called tracking) may appear on the inner surface of
(b) Reseal the tank after inspection and
the interrupter or shields, due to electrostatic
charging current. This is usually aggravated by a
deposit of carbon sludge, which has previously been
(c) Refill the tank to the proper oil level and
generated by some interrupting operation. If the
inspect for leaks.
circuit breaker has remained closed and is carrying
(2) Circuit breakers insulated with
current, evidence of heating of the contacts may be
move SF, gas from the circuit breaker; transfer the
found if the contact surfaces were not clean, have
gas from the circuit breaker (use a gas processing
oxidized, or if the contact pressure was improper.
unit); pull a vacuum on the circuit breaker to be
Any shrinkage and loosening of wood or fiber parts
certain that all of the gas has been removed; and
release the vacuum on the circuit breaker with dry
(due to loss of absorbed moisture into the dry oil)
air or nitrogen to avoid pulling moisture into the
will take place following the circuit breaker instal-
lation, independent of the circuit breaker operation.
(a) Inspecting the tank includes opening the
However, mechanical operation will make any loos-
tank, vacuuming any residue (if present), ventilat-
ening more evident. If possible, before inspection,
ing, and wiping the inside of the tank with approved
open and close the circuit breaker while energized.
If this is not possible, additional information may be
(b) Inspect all parts for wear and damage,
gained by operating the deenergized circuit breaker
including the fiberglass components and seals.
several times, measuring the contact resistance of
(c) Install factory-recommended overhaul
each pole before and after each operation.
and sealer kits. Replace all desiccant materials, if
(2) Influence of normal duty. The severity of
duty imposed by load switching, line deenergizing,
(d) Perform any repairs or adjustments.
and fault interruptions depends upon the type of
(e) Seal the circuit breaker tank and pull a
circuit breaker involved. In circuit breakers which
vacuum in accordance with manufacturer's specifi-
employ an oil blast generated by the power arc, the
cations. If the vacuum holds for the specified
interruption of low current faults or line charging
amount of time, this indicates that no leaks are
current may cause more deterioration, because of
low oil pressure, than the interruption of high cur-
(f) Refill the tank to the proper pressure.
rent faults. In some designs using this basic prin-
ciple of interruption, distress at low interrupting
e. Typical internal circuit breaker problems. Evi-
duty is minimized by multiple breaks, rapid contact
dence of the following tendencies indicate internal
travel, and turbulence of the oil caused by move-
problems which need to be corrected.
ment of the contact and mechanism. In designs em-
(1) Loosening of keys, bolts (especially fiber),
ploying a mechanically driven piston to supplement
cotter pins, operating rods, supports, and guides or
the arc-driven oil blast, the performance is more
an indication of wear or weakness.
uniform. Better performance is yielded b y designs
(2) Formation and accumulation of carbon or
which depend upon a mechanically driven oil blast
sludge in the interrupter or on bushings.
for arc interruption. In this type, contact erosion
(3) Indication that th e interrupter is inclined
may appear only with heavy interruptions. The me-
to flash over and rupture the static shield or resis-
chanical stresses that accompany heavy interrup-
tor or interrupter parts or barriers are disposed to
tions are always more severe. These variations of
burn or erode.
performance among various designs must be consid-
(4) Indication that bushing gaskets have
ered when evaluating the need for maintenance and
leaked moisture into the circuit breaker insulating
performance of a circuit breaker. Because of these
variations, the practice of evaluating each fault in-
terruption as the equivalent of 100 no-load opera-
(5) Cracks in any of the above parts.


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