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54
Maintenance
01.4IB.51000C
PowlVac® Metal-Clad Switchgear
5kV & 15kV
13) Testing
The condition of each switchgear unit at
the time of inspection, should be listed in
a permanent record to become a guide for
anticipating the need for replacements, or
for special attention between the regular
maintenance periods.
a. Insulation resistance tests are suggested
for checking the insulation. A series of
these tests will indicate any tendency
towards a reduction in the dielectric
strength of the insulation. Insulation
resistance readings should be
taken before and after cleaning the
switchgear equipment, and in so far
as possible, under similar conditions
at successive periods. Records should
include the insulation resistance
reading, the temperature, and the
humidity (either by definite reading or
description).
b. Acceptable limits will vary with the
extent and design of the bus structure.
In contrast to a small installation, the
longer switchgear lineups will have
a more extensive bus structure with
a greater number of insulators, and
thereby, a larger number of parallel
insulation resistance paths to ground,
which will tend to decrease insulation
resistance readings. This variation in
insulation resistance between different
switchgear lineups emphasizes the
value of a series of readings that can be
charted to establish a normal insulation
level so that progressive weakening
of the insulation can be recognized.
Voltage transformers and control power
transformers should be disconnected
during these tests, as they may not be
able to withstand the switchgear tests
and they may provide direct paths to
ground.
c. The resistance of bus connections may
be checked by passing a measured
DC current of 200A or more, through
the joint and measuring the voltage
drop (in millivolts) across the joint. An
increase in the voltage drop indicates a
joint requiring maintenance.
d. Tests on circuit breakers, removable
elements, and other devices which
are included in the switchgear should
be performed in accordance with the
instructions applicable to each device.
14) Doors
Verify that all doors open without
interference.
a. Exterior doors utilizing tie-down bolts
should have gasket material around
the tie-down bolt holes. Confirm
the presence and functionality of
the gasket. If the gasket is damaged,
replace it.
b. 3000A doors have a ventilation pattern
of rectangular slots. Make sure all slots
are open and air flow is possible, not
blocked by foreign objects.