Capacitor Bank Calculator
Bank the kvar — kvar, volts and hertz into microfarads per phase, delta against star.
Capacitor Bank Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Balanced three-phase; single banks, no steps or detuning reactors
- Sinusoidal supply — harmonic environments need detuned units
In short: 30 kvar of correction at 480 V, 60 Hz, wired delta: 115.13 µF per phase — each capacitor sees the full 480 and three of them split the duty. Rewire the same bank star and every leg sees only 277.128129 V, so it takes 345.39 µF per phase to deliver the same kvar. The bank draws 36.084392 A of line current — 30 kvar of burden removed from the utility's side of the meter.
Formula
CΔ = kvar × 1,000 ÷ (3 × 2πf × V²); C_Y = 3 × CΔ
A capacitor's reactive power is 2πfCV² at the voltage it actually sees. Delta wiring puts every unit across the full line voltage, so three units deliver 3 · 2πfC·V² — divide the kvar target by it for the per-phase capacitance. Star wiring puts each unit on V/√3, and since kvar scales with voltage squared, star needs three times the microfarads for the same correction. Same kvar, very different capacitor — the wiring is a purchasing decision.
Worked Example
- Enter the kvar target from the power-factor math.
- Enter the line voltage and mains frequency.
- Read the delta microfarads, the star alternative, and the line current.
Defaults: 115.13 µF delta, 345.39 µF star, 36.084392 A. Drive the frequency to 50 Hz and the bank grows to 138.155 µF — capacitance scales with 1/f, the 50 Hz world's small tax.
Strengths & Limits Of This Model
Where this engine is strong
- Delta AND star priced side by side — the wiring is the decision
- The 1/f law shown live at 50 Hz
Where it stops
- Stepped automatic banks need per-stage sizing
Practical Use Cases
Bank orders
microfarads off the kvar target
Rewiring checks
what star costs in capacitance
50 Hz conversions
the 1/f rescale
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Capacitor Bank Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why does star need three times the capacitance?
Because kvar scales with voltage SQUARED, and each star leg sees 1/√3 of the line voltage: (1/√3)² = 1/3 the kvar per microfarad. Delta puts the full line on every can — fewer, beefier capacitors; star spreads the work across more.
How is the 115.13 µF computed?
Reactive power per phase is 2πfCV²; three delta phases make 3 · 2πfC·V². Solve for C: 30,000 var ÷ (3 × 376.99 × 480²) = 115.13 µF. The frequency and the square of the voltage are the whole sensitivity.
What happens at 50 Hz?
The same kvar needs 6/5 the capacitance — 138.155 µF against 115.13, exactly the 60/50 ratio. A 60 Hz bank moved to a 50 Hz grid delivers only 83% of its nameplate kvar, quietly.
What current does a bank draw?
Line current is kvar ÷ (√3 · V): the default 30 kvar bank draws 36.084392 A — leading current that cancels the load's lagging amps upstream of the connection point.
Delta or star in practice?
Delta dominates low-voltage power-factor correction: smaller capacitors per unit, and a failed unit does not leave the bank floating the way an open star point does. Star appears at medium voltage where per-unit ratings rule.
Why do banks step in blocks?
Fixed capacitance over-corrects at light load, and leading power factor has its own sins — voltage rise and resonance risk. Contactors step units in so the kvar follows the load's lagging curve.
What is the resonance danger?
A bank's C and the system's source inductance form an LC pair; if a harmonic lands on that frequency, amplification eats the bus. Utilities and factories detune banks with series reactors for exactly this reason.
Does the bank save energy?
It saves current, not kWh at the load — the gains are the removed I²R losses (current, squared), the released transformer capacity, and the penalty line on the bill. The kWh meter barely notices; the demand meter does.