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Manual operation
The switch may be manually opened and closed by operat-
ing the yellow handle under the sleet hood.
Manual operation does not affect the status of the
N
ote:
electrically operated actuator. To electrically close
a switch which has been manually opened, the
electrical open circuit must be first activated to
change the status of the selector switch for a close
operation.
Oil condition
Oil plays an important role in the proper functioning of
the switch. It provides the internal insulating barrier from
phase to ground, and acts as an arc quencher. Switching
operations cause reductions of some of the oil into
chemical compounds, free carbon and gases. Some of
these compounds form water-absorbing particles which
reduce the dielectric strength of the oil. For effective switch
operation the oil must be replaced before it deteriorates
below a safe level. Oil that has been contaminated with
carbon sludge or has a dielectric strength of less than 22 kV
should be replaced.
Used oil must be reconditioned before using. Filtering may
remove absorbed and free water, and other contaminants to
raise the dielectric strength to an acceptable level. However,
it does not always remove water-absorbing contaminants.
Thus, the dielectric strength of the oil may fall rapidly after
the switch is returned to service. Therefore the switch
should be filled with new oil or oil that has been restored to
like-new condition. Oil used in these switches conforms to
ASTM Standard D3487 , Type 2; its property limits are listed
in Reference Data R280-90-1, Oil Specifications and Tests.
New oil should always be filtered before using even
though it is obtained from an approved source. Passing oil
through a blotter press will remove free water and solid
contaminants such as rust, dirt, and lint. When filtering
the oil, aeration should be kept to a minimum to prevent
moisture in the air from condensing in the oil and lowering
its dielectric strength.
Insulation level withstand tests
High-potential withstand tests provide information regarding
the dielectric condition of the switch. Testing is performed at
75% of the rated low-frequency withstand voltage (Table 3).
Table 3. Test Voltages for Insulation Level Withstand
Test
Switch Type
BIL (kV)
NR
95
NR*
125
* Extra creepage bushings
Test Voltage (kV)
35.0
42.0
TYPE NR OIL SWITCH MAINTENANCE INSTRUCTIONS MN230001EN February 2016
Test 1: Proceed as follows:
1.
Close the switch.
2.
Ground switch tank and head.
3.
Apply proper test voltage to one of the bushing
terminals.
The switch should withstand the test voltage for 60
•
seconds.
Test 2: Proceed as follows:
1.
Open the switch.
2.
Ground switch tank and head.
3.
Ground the bushing on one side of the switch.
4.
Apply proper test voltage to the ungrounded bushing.
The switch should withstand the test voltage for 60
•
seconds.
5.
Reverse the test and ground connections to the
bushings.
6.
Again apply proper test voltage to the ungrounded
bushing.
The switch should withstand the test voltage for 60
•
seconds.
Test results:
These high potential withstand tests provide information on
the dielectric condition of the switch.
1.
If the switch passes the closed-contacts test (Test 1)
but fails the open-contacts test (Test 2) the cause is
likely to be in the main contact assembly.
2.
If the switch fails the closed-contacts test (Test 1) the
cause is likely to be a diminished electrical clearance or
failed insulation.
3.
After correcting the problem, retest to confirm the
repair.
5
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