Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - Classic Control - Manual (Page 308)

6-18 Component Definition and Maintenance
7000-UM150I-EN-P – June 2013 7000 “B” Frame
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.
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
Phase - Neutral L1-N L2-N L3-N
Test Voltage 200V 200V 200V
Measured Current 1.87A 1.866A 1.861A