Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 363)

Component Definition and Maintenance 6-19
7000 “C” Frame 7000L-UM300I-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,
29.2

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.