Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive - Air-Cooled (A Frame) - Manual (Page 286)

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Component Definition and Maintenance
7000A-RM001A-EN-P – January 2011 7000 “A” Frame
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. (Refer to “Filter
Capacitor Replacement” guidelines in the Classic User Manual -
Component Definition and Maintenance chapter (Chapter 6) for using
proper torque when reconnecting the capacitors)
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.
A T T E N T I O N A T T E N T I O N 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 stock or other
voltage-measuring device, verify that the capacitor
is fully discharged before touching it.
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 +15% of the
capacitor nameplate micro-Farad. If it is outside this range then the
capacitor must be replaced.
Example: An example is given below to illustrate how the capacitance
value is calculated.
e.g. - the capacitor under test is rated at 400 kVAR, 6600 V, 50 Hz,
29.2µF. You are using 200 V, 50 Hz test power and have recorded the
values of voltage and current for each test as given in the table below.
Phase - Neutral L1-N L2-N L3-N
Test Voltage 200V 200V 200V
Measured Current 1.87A 1.866A 1.861A
D.C. Link / Fan / Control
Components (cont.)