Power-Factor Correction Capacitance
Worked example: 5 kvar at 240 V, 60 Hz → 230.26 µF — press Try an example to run it live, then adjust anything.
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Power-Factor Correction Capacitance explained
A capacitor's vars are Q = V²/XC, and since XC = 1/(2πfC), that rearranges to Q = 2πfCV² — solve it for C and you have your capacitor. Getting 5 kvar at 240 V and 60 Hz takes 5000/(2π × 60 × 240²) ≈ 230 µF, a physically large oil-filled can, which is why correction capacitors are bulky and why higher voltages are so much cheaper per var. The var field here uses watts: vars and watts share dimensions.
The V² is the sting. A capacitor bank rated 25 kvar at 480 V delivers only 25 × (240/480)² ≈ 6.25 kvar if someone installs it on a 240 V system — a mistake that shows up as a stubbornly unimproved power factor. Frequency matters the same way, so a bank imported from a 50 Hz country loses a fifth of its vars at 60 Hz... and gains 20% the other way, along with the overcurrent that comes with it.
Power-Factor Correction Capacitance formula
- = Capacitance (μF)
- = Reactive power wanted (var) (W)
- = Supply frequency (Hz)
- = Voltage across the capacitor (V)
Missing one of these? Work it out first, then come back
- Capacitance — Q Factor of a Series Resonant Circuit, RC Cutoff Frequency
- Reactive power wanted (var) — Reactive Power (Power Triangle), Power-Factor Correction kvar
- Supply frequency — Synchronous Speed from Frequency and Poles, 555 Astable Frequency
- Voltage across the capacitor — Uniform Field Between Parallel Plates (E = V/d), Three-Phase Real Power