3 Phase Systems (Problem)

[JohnielWhite]

Could someone tell me the general approach for a problem of this nature or lead me to useful information.
Problem
A 415V, 50Hz, three-phase motor takes a line current of 15A when operating at a lagging power factor of 0.65. When a capacitor bank is connected across the motor terminals, the line current is reduced to 11.5A. Calculate the kVAR rating and the capacitance per phase of the capacitor bank for:
1) A star connection
2) A delta connection
Find also the new overall power factor.

Any response will be greatly appreciated.

 

[Valkarie]

The general approach for a problem of this nature is to first calculate the total kVAR of the capacitor bank (by subtracting the old power factor from the new power factor and then multiplying by the total apparent power). Then, you need to find the capacitance per phase by dividing the total kVAR by the square of the voltage. Finally, you need to calculate the new overall power factor by dividing the real power (calculated using the new current and voltage) by the total apparent power.