Rockwell Automation Publication 7000L-UM301F-EN-P - March 2020
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Component Definition and Maintenance
Chapter 5
Testing Filter Capacitors
1.
Ensure there is no power to the equipment before testing the capacitor.
2.
Follow appropriate safety steps to isolate the equipment from medium
voltage.
3.
Verify that there is no voltage present on the capacitor by using a hot stick
or any other appropriate voltage-measuring device.
4.
Perform visual inspection to confirm there is no oil leak or bulge in any of
the capacitors.
5.
Note the location of all the cables and mark them accordingly.
6.
Disconnect power cables from the capacitor terminals on all four bushings
and isolate them from the capacitor.
7.
Connect a low voltage single-phase test power, for instance 110V or 220V,
across a phase and the neutral of the capacitor. Switch on the test power
and measure the test voltage and current drawn by the capacitor. Repeat
the test for all three phases and note down the test voltage and current.
8.
Now, calculate the capacitance from the measured values of test voltage
and current. For a good capacitor, the calculated capacitance value for each
of the three readings should be within ±10% of the capacitor nameplate
micro-Farad. If it is outside this range then the capacitor must be replaced.
ATTENTION:
To prevent electrical shock ensure the main power has
been disconnected before working on the capacitor. Verify that all
circuits are voltage free using a hot stick or appropriate voltage-
measuring device. Failure to do so may result in injury or death..
ATTENTION:
Verify the load is not running due to process. A
freewheeling motor can generate voltage that will be back-fed to the
equipment being worked on.
ATTENTION:
The capacitor will charge during this test so care must be
taken to prevent a shock or injury. When moving the test connections
from one phase to the next, wait for at least five minutes until the
capacitor is discharged. Using a hot stick.
