Quantcast Switch maintenance -Cont.

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TM 5-684/NAVFAC MO-200/AFJMAN 3 2 - 1 0 8 2
(2) Visual aids. Binoculars can facilitate spot-
that may be present. Refer to chapter 3, section IV
The presence of an excessive amount of contamina-
ting switches that are obviously in need of repair or
maintenance because of broken insulators or other
tion should be reported to the supervisor, as the
--
parts. Visual inspection of a wet switch, or the use
persistence of such a condition may require correc-
of a temperature-scanning detector,. may indicate
tive measures.
(3) Mounting. Check mountings for evidence of
hot spots which are possible sources of trouble. Di-
rectional microphones or ultrasonic detectors can be
rust and corrosion and to ensure proper alignment
used to locate local corona sources needing removal.
and securement. Ground connections must be tight.
b. Scheduling. A relatively small amount of
(4) Blades. The blade or movable contact of the
maintenance is required on modern switches, so
switch should be inspected for evidence of overheat-
where possible, it is recommended that the schedule
ing, which may be indicated by discolorations. If
for such maintenance be coordinated with that of
overheating is caused by poor contact, it should be
associated equipment. Schedule special inspection
corrected when contacts are adjusted and cleaned.
and maintenance whenever the switch has carried
Switches that appear to be overheated, due to load
heavy short-circuit current.
currents in excess of rating, should be reported to
the supervisor.
c. Checking. Examination of de-energized and
(5) Blade Latch. A blade latch is used on a hook
grounded switches should include the following
stick operated switch to hold blade in closed posi-
items:
tion. Such a switch should be checked in the closed
(1) Operating mechanism. Check the adjust-
position, to determine whether the catch is func-
ment of the operating mechanism, operating rod,
tioning properly.
and interphase tie rods (if used) to ensure simulta-
(6) Contacts. Contacts should be cleaned and
neous and smooth operation of the switch blades.
adjusted in accordance with manufacturer's instruc-
Mechanisms should be cleaned and lubricated only
tions. Modern switches are normally designed so
when so recommended, and then in accordance with
that the contacts are self-cleaning, by virtue of the
the manufacturer's instructions. (Many modern
opening and closing action of the switch. After a
switches are built with self-lubricating bearings.)
switch remains in either position for a long time, it
Examine all metallic parts of an operating mecha-
should be operated several times during a mainte-
nism including operating handle connection for
nance inspection. This operation will clean the con-
signs of rust, corrosion, and loose or broken connec-
tact surfaces. Operate only after getting clearance
tors. Switches located outside of a fenced and locked
and after the circuit has been deenergized.
area, and having operating handles at ground level,
(a) Do not use a coarse abrasive to clean con-
require locking provisions on handles for both the
tacts. If contact pitting is minor, smooth the surface
open and closed positions. Switches located within a
with clean crocus cloth or as the manufacturer rec-
fenced and locked area, are subject to local regula-
ommends.
tions for locking.
(b) Where arcing horns are used, ensure that
(a) Inspect all live parts for scarring, goug-
they make contact, as intended, during opening and
ing, or sharp points, which could contribute to ex-
closing operations.
cessive radio noise and corona. Check corona balls
(c) A nonoxidizing lubricant should be used
and rings for damage which could impair their ef-
to protect the contacts against oxidation and to lu-
fectiveness.
bricate the blade hinge. Silicone greases are excel-
(b) Power-operating
mechanisms
for
lent for this purpose, as they are relatively unaf-
switches are usually of the motor-driven, spring,
fected by changes in temperature and are highly
hydraulic, or pneumatic type. Follow the manufac-
water resistant.
turer's instructions with regard to the limit switch
(7) Terminals and connections. Terminals
adjustment. Check associated relay equipment for
poor contacts, burned out coils, and adequacy of
should be checked to ensure that they are secure.
supply voltage. The complete electrical circuit of a
Connections showing evidence of heat should be cor-
motor-operated mechanism should be checked to en-
rected as a high-resistance contact is indicated.
sure proper operation and wiring which is secure
(8) Interrupting elements. Load interrupter
and free of insulation defects.
switches are equipped with an interrupter element,
(c) Inspect, check, and test all safety inter-
designed to quench the arc that results when the
locks for proper operation.
switch is opened under loaded conditions. Basically,
(2) Insulators. Examine insulators for cracks,
these elements are shunt devices, installed as part
of the switch, through which current passes only as
chips, breaks, and evidence of flashover. Bad insu-
the switch is opened. In some designs the arc
lators should be replaced. Insulators should be
quenching medium is air, but for the higher voltage
cleaned to remove any contaminating materials
8-5





 


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