Inverters and conductors are limited by apparent power and current—reactive kVAR is part of that budget. This guide shows how to calculate kVAR for inverter and conductor sizing from load kVA, power factor, and the real kW your motors actually draw.
Benefits
- kVAR = √(kVA² − kW²) after kW = kVA × PF.
- kVA (not kW) drives breaker and inverter nameplate checks.
- Document kVAR in BOM for motor-heavy distribution quotes.
How it works
- Sum load kVA—or use a single motor branch kVA from nameplate.
- Enter power factor (measured or motor catalog typical).
- Read kVAR and kW; verify inverter kVA ≥ load kVA, not just kW.
FAQ
How do I calculate kVAR for inverter sizing?
From kVA and PF: kW = kVA × PF, kVAR = √(kVA² − kW²). Example: 8 kVA load at 0.8 PF → kW = 6.4, kVAR ≈ 4.8. Inverter must supply 8 kVA apparent—a 6.4 kW-rated inverter may trip if its kVA limit is only 7 kVA.
Why does kVAR affect conductor sizing?
Current depends on apparent power I = kVA × 1,000 ÷ (V × √3) on three-phase (or kVA × 1,000 ÷ V single-phase). Reactive kVAR increases kVA at the same real kW, raising amps without more useful work. Size feeders on calculated kVA including kVAR.
Can I reduce kVAR for sizing?
Power-factor correction capacitors at the load or panel reduce lagging kVAR, lowering apparent kVA and current. Calculate kVAR first to see if correction is cheaper than upsizing cable or inverter kVA. After correction, re-run with improved PF.
Technical specifications
- kVAR = √(kVA² − kW²).
- kVA_sizing ≥ √(kW² + kVAR²).
- I ∝ kVA at fixed voltage (per phase rules apply).
- Related: inverter-sizing, kva-to-kw, power-factor-and-reactive-power-calculator.