Rockwell Automation 7000A PowerFlex Medium Voltage Drive (A-Frame) - Classic Control - Manual (Page 359)

Component Definition and Maintenance 6-55
7000 “A” Frame 7000A-UM150F-EN-P –June 2013
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.
Example: An example is given below to illustrate how the capacitance
value is calculated.
Suppose a capacitor under test is rated at 400kVAR, 6600V, 50Hz, 9.2

F.
Let us say, you are using 200V, 50Hz 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
Let us calculate the capacitance using the first reading. In this case:
V = 200V, I = 1.87 for L1-N
Xc = V/I = 200/1.87 = 106.95
F C
C
Xc f
C


7 . 29
95 . 106 50 14 . 3 2
1
2
1

  


Where, f = frequency of the applied voltage.
Similarly, you can calculate the capacitance for the remaining two
measurements for L2-N and L3-N.