Quantcast Vacuum interrupting units

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TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
dielectric strength before using, with breakdown
load pickup. Never hold the operating lever of series
coil reclosers in a closed position in an attempt to
across a standard O.l-inch (2.54-millimeter) gap oc-
pick up cold load.
curring at not less than 26 kilovolts root mean
b. Frequency of maintenance. Provide mainte-
square (rms), the minimum acceptable dielectric
nance after a number of operations, or after a time
strength for new oil. Breakdown at a lower test
interval, in accordance with the manufacturer's rec-
voltage usually indicates excessive moisture in the
ommendations, local operating experience, or a com-
oil. Remove any moisture by filtering before the oil
bination of these.
is used. Always test the oil before putting back in
(1) Maintenance based on elapsed time. Operat-
service a recloser which has been temporarily re-
ing service and local conditions influence mainte-
moved for repair. Replace with clean dry oil if the
nance frequencies. Inspect initially in accordance
dielectric strength of the oil is less than 22 kilovolts
with the manufacturer's recommendations. Humid-
rms.
ity and temperature can affect the frequency of nec-
(2) Vacuum interrupting units. Leaks caused
essary maintenance. Therefore, a study of mainte-
by excessive mechanical strain, insufficiently
nance records extending over several years can be
degassed contact materials, or other causes may
helpful in determining proper maintenance sched-
decrease the unit's dielectric strength. The dielec-
ules on large facilities.
tric strength of the vacuum gap can be tested with a
(2) Maintenance based on number of opera-
60-hertz high-potential test at the manufacturer's
tions. Reclosers may be maintained after a certain
recommended voltage.
number of operations, determined from the recloser
operation counter readings. A procedure for evaluat-
(a) Adjust vacuum contacts for proper con-
ing useful life of an oil-filled recloser, based on stan-
tact opening travel, contact closing overtravel, and
dard duty, is given in ANSI C37.61/IEEE 321, ap-
contact closing force, according to the manufactur-
pendix B but is not recommended for use by
er's recommended procedure.
maintenance  personnel.
(b) X-radiat'ion may be produced when
(3) Mainten ance based on elapsed time and
vacuum interrupters are energized above maximum
number of operations. The use of time interval alone
rated voltage. Follow the manufacturer's required
does not take into account the frequency and sever-
precautions.
-
ity of the recloser operations. On the other hand,
(3) Units insulated with SF, gas. Follow the
use of the number of operations alone ignores
manufacturer's recommendations as to the insulat-
elapsed time, during which the insulating medium
ing medium treatment.
may have deteriorated.
(4) Tests. Test in accordance with the limits set
(4) Suggested frequency. An industry-suggested
by the manufacturer and in accordance with
method of combining the elapsed time and opera-
ANSI/IEEE C37.60.
tion factors is as follows: Maintenance, internal in-
(a) Insulation. Aging, moisture, and the
spection, and testing of reclosers should be per-
sludge deposits can cause insulation on fiber parts
formed at 100 operations or every 3 years,
and wiring to deteriorate. Test insulation by a 60-
whichever occurs first if no better basis can be es-
hertz high-potential test, by power factor measure-
tablished.
ment, or by dc insulation tests.
c. Field inspection. After installation, a recloser
(b) Minimum tripping current. Make a mini-
should be carefully inspected at the established in-
mum tripping current test to determine that the
terval. An inspection should include examining the
recloser trips at the proper current value.
bushings for cracks, as well as other items recom-
(c) Time-current characteristics. Make a
mended by the manufacturer. Inspect oil-insulated
time-current characteristic test in accordance with
unit tanks for leakage. Record the counter reading.
the manufacturer's maintenance manuals and plot
Bypass and isolate the recloser by suitable means, if
to compare with the manufacturer's values. Permis-
possible, and perform an operating test. Manually
sible tolerance from rated characteristics are plus or
operate the recloser several times to the lockout
minus 10 percent of time or current, whichever is
position, by means of a switch stick or other control.
greater.
Operating tests can disclose possible troubles and
(d) Lockout. Check new or reconditioned
do prevent the accumulation of high-resistance ox-
reclosers by operating them through their sequence
ides on contact surfaces.
to lockout. The procedure will vary dependent upon
d. Maintenance. Give the following items particu-
the make and type of recloser.
lar attention:
(1) Oil-insulated unites. Never assume that
(e) Reset. Check the resetting time of a
new oil is free of moisture. It should be tested for
recloser during the lockout test.
8-15





 


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