Capacitor needed for phase angle change (RLC network)

1 reply · 1K views · last reply
D.B0004
Messages
16
Reaction score
0

Homework Statement


An inductive load is connected to a 120V (rms), 60Hz AC source. The load draws 5.0 kW at a power factor of 0.81 (lagging). You need to improve your power factor to 0.96 (lagging) by adding a capacitor.

What is the Capacitance needed (in uF)?

Homework Equations


P/|S| = cos(phi)
Q = V^2/X
S = sqrt(P^2 + Q^2)

The Attempt at a Solution


Please see photo with my solution attached. My professor says the answer is actually 398.17uF. I did this problem multiple times and never got that answer. I keep getting what I got in the photo attached (271uF).
 
Attachments
  • Handwritten calculation on lined paper, rotated sideways: a power triangle with P = 5 kW, angle 35.9 degrees, S = 2.73215 kVA; then |S| = 5/0.81 and related steps, ending with C = 271.44 uF.
    IMG_1295.JPG
    51.7 KB · Views: 499
It's hard to make out your work in that sideways photo. Can you explain your approach?