Power factor correction calculator
Find the capacitor kvar to lift a power factor.
Reads AS/NZS 3000:2018.
Try a job 6
Each job fills in example values. Replace them with your values.
- Correct a factory power factorThe kvar and bank steps to lift a 250 kW load from 0.78 to 0.95.
- Free supply capacity with power factor correctionThe kVA a 400 kVA site gets back when its power factor rises to 0.98.
- Correct a motor boardThe kvar to lift a 75 kW motor load from 0.82 to 0.95.
- Choose the capacitor stepsThe bank in 25 kvar steps for a 300 kVA load.
- Check a bank for resonanceThe bank against the fault level and 20 % harmonic load.
- Correct a single-phase loadThe kvar for a 15 kW single-phase load at 0.7.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Phases
- Three phase
- Voltage
- 400 V
- Load unit
- kW
- Load
- 100
- Present power factor
- 0.75
- Target power factor
- 0.95
- Bank step
- 25 kvar
- Current harmonic distortion (THDi)
- 0 %
- Fault level at the bank
- 0 MVA
Correction required
55.32kvar
- Bank installed
- 3 × 25kvar
- Power factor with the bank
- 0.991
- Current before
- 192.45A
- Current after
- 145.59A
- Released capacity
- 32.47kVA
- Bank conductors, at least
- 146.14A
This result is a design aid. Verify it against the current standard.
Calculation steps
- Real power100kW
- Reactive power at the present power factor88.19kvar
- Reactive power at the target power factor32.87kvar
- Correction requiredResult55.32kvar
- Bank steps
3 × 25 kvar
- Power factor with the bank0.99
- Current before192.45A
- Current after145.59A
- Released capacity32.47kVA
- Rated current of the bank108.25A
- Least capacity of the bank conductors, 135 %146.14A
AS/NZS 3000:2018 Cl 4.15.2.3
About this calculator
How this is calculated
The tool finds the capacitor bank that lifts a load to a target power factor. It then gives the current before and after.
- Real power. You enter kW, or kVA with a power factor. The tool finds the real power.
- Reactive power. It finds the reactive power at the present power factor. It does the same at the target.
- Correction required. The difference is the kvar the bank must supply.
- Bank steps. It rounds up to whole steps of the size you enter. It then recalculates the power factor with that bank.
- Currents. It finds the current before and after. The difference is the capacity the bank releases.
- Bank conductors. It sizes the bank conductors at 135 % of the bank rated current. This follows AS/NZS 3000 Cl 4.15.2.3.
AS/NZS 3000 Cl 4.15.2.2 covers switching, and Cl 4.15.3.1 covers discharge.
Worked example
- 100 kW three-phase load at 400 V, 0.75 to 0.95, 25 kvar steps. The correction required is 55.32 kvar. The bank is 3 × 25 kvar. The power factor with the bank is 0.991. Current falls from 192.45 A to 145.59 A. The released capacity is 32.47 kVA. The bank conductors need at least 146.14 A.
Limits
The tool does not assess harmonics unless you enter the THDi. Switch each step with a device rated for capacitors. The tool does not model resonance with the supply.
See also: Power factor and reactive power, Power factor correction for a 250 kW factory and Three phase power.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
How is the kvar worked out?
The tool finds the reactive power at the present power factor and at the target, both from the real power. The difference is the kvar the bank must supply. It then rounds up to whole bank steps.
Why does the current fall after correction?
The real power stays the same, but the bank supplies the reactive power on site. So the supply carries less apparent power. The current falls in proportion, and the kVA it frees is the released capacity.
When do I need a detuned bank?
Drives, rectifiers and LED drivers draw harmonic currents. Plain capacitors can resonate with the supply and amplify them. As a rule of thumb, above about 10 % THDi fit a detuned bank with series reactors. Above 20 %, get a harmonic study.
What does the resonance order mean?
A capacitor bank and the supply form a tuned circuit. The order is the square root of the fault level over the bank kvar. Near the 5th, 7th, 11th or 13th harmonic, the tool warns you.
Clauses and tables this tool reads
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