Quantcast Maintenance of nonmetalclad switch gear circuit breakers -Cont.

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TM 5-684/NAVFAC M O - 2 0 0 / A F J M A N 32-1082
An abnormal increase in the resistance of this cir-
kilovolts, even though some manufacturer's instruc-
cuit may indicate foreign material in the contacts,
tions allow 16 kilovolts. If the oil is carbonized,
loose contact support, loose jumpers, loose bushing
filtering may remove the suspended particles, but
connections, or corrosion. Any one of these may
the interrupters, bushings, and other internal parts
cause localized heating and deterioration. Measure
must be wiped clean. If the dielectric strength has
been lowered by moisture, check and eliminate the
resistance of the main contact circuits with a por-
table double bridge (Kelvin) or a "Ductor." The cir-
source of the moisture (such as fiber or wood parts);
cuit breaker contacts should not be opened during
and dry the affected parts thoroughly before placing
this test, because of possible damage to the test
the circuit breaker in service.
equipment. Compare resistance values to the manu-
(2) Circuit breakers insulated with SF,. Circuit
facturer's values or to values found on a similar
breakers having SF, insulation should be tested
circuit breaker. These values should not vary more
every 3 months during the first year of service, and
than 25 percent between poles.
at least every 12 months thereafter, to determine
(9) Motion analyzers can provide graphic
the moisture content of the SF, gas. Moisture con-
records of close or open initiation signals; contact
tent must also be tested when gas is added. Service
closing or opening time with respect to initiation
equipment according to the manufacturer's instruc-
signals; contact movement and velocity; and contact
tions. Moisture content should be less than 50 parts
bounce or rebound. Circuit breaker motion analyz-
per million by volume (ppm,). Do not energize a
ers are portable devices designed to monitor the
section of the gas-insulated equipment, if the SF,
operation of power circuit breakers, as they permit
gas density is less than 50 percent of nominal or if
mechanical coupling of the motion analyzer to the
the moisture content of the gas exceeds 1000 ppm,.
circuit breaker operating rod. The records obtained
Refer to chapter 15, section II in regard to the tox-
not only indicate when mechanical problems are
icity of SF, gas.
present, but also help isolate the cause of the prob-
c. Internal inspection guidelines. When an inter-
lems. Obtain a motion-analyzer record on a circuit
nal inspection is required it should be made at the
breaker when it is first installed. This will provide a
same time as an external inspection. The circuit
master record which can be filed and used for com-
breaker tanks or contact heads should be opened
parison with future maintenance checks. Tripping
and the contacts and interrupting parts inspected.
and closing voltages should be recorded on the mas-
Follow these guidelines and the checklist furnished
ter record, so subsequent tests can be performed
by the manufacturer. Such a checklist may provide
under comparable conditions. Time-travel records
forms useful for recording inspection and mainte-
are taken on the middle pole from the operating
nance data.
mechanism.
(1) Internal difficulties are most likely to ap-
(10) Check the air system of a pneumatic
pear early in the use of a circuit breaker, which is
mechanism for leaks.
why early internal inspections are recommended.
(11) Check control wiring for loose connections.
As unsatisfactory internal conditions are corrected,
and if one or two later inspections indicate satisfac-
(12) Check the settings of compressor switches,
tory internal conditions, the frequency of internal
low pressure alarms, and cut-off switches.
inspections may safely be decreased.
(13) Inspect and check the operating mecha-
(2) For circuit breakers equipped with pneu-
nism. Lubricate all pins, bearings, and latches, us-
matic operators, drain and inspect the air tanks.
ing the recommended lubricant.
(3) Perform post maintenance diagnostic tests
b. External inspection guidelines specific to the
on circuit breakers in accordance with instructions
insulating medium used. Oil dielectric tests are
from test equipment and circuit breaker manufac-
needed for oil circuit breakers, and a moisture test
turers, and follow established maintenance proce-
should be provided for gas-insulated units.
dures.
(1) Oil-insulated circuit breakers. Check oil di-
(4) Test operate the circuit breaker and record
electric strength, power factor, acidity, and color.
the number of operations. The tests should include
The dielectric strength must be maintained to pre-
all alarms (including control alarms), switches, and
vent internal breakdown under voltage surges and
the manufacturer's recommendations.
to enable the interrupter to function properly. Its
d. Internal inspection guidelines specific to the
action depends upon changing the internal arc path
insulating medium used. The insulating medium
from a fair conductor to a good insulator, in the
must be removed, as necessary, to examine the cir-
short interval while the current is passing through
cuit breaker internally.
zero. A manufacturer's instructions should state the
lowest allowable dielectric strength. However, the
(1) Oil-insulated circuit breakers. Inspecting
dielectric strength should be maintained above 25
the tank includes removing the oil, ventilating the
8-8





 


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