Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C-Frame) - ForGe Control - Manual (Page 286)

286 Rockwell Automation Publication 7000L-UM301D-EN-P - June 2014
Chapter 5 Component Definition and Maintenance
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 demonstrate how the capacitance value is
calculated.
Suppose a capacitor under test is rated at 400kVAR, 6600V, 50Hz, 29.2 μF. 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:
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
V 200 V I 1.87for L1-N = , =
Xc V I § 200 1.87 § 106.95 = = =
C 1 2 fXc § =
C 1 2 3.14 ¥ 50 ¥ 106.95 ¥ § =
C 29.7 F =