kVAR
TILAK BHUSAL / ENGINEERING TOOLS
Power factor.
Real savings.
Size compensation. Recover capacity. Understand your demand bill.
ELECTRICAL UNITS · kW / kVA / kVAR · Balanced three-phase
THE ELECTRICAL ENGINEERING BEHIND THE NUMBERS
Correct the load. Check the whole system.
Qc = P(tan θ₁ − tan θ₂)
Correct the lagging fundamental reactive demand. Automatic steps match the bank to the changing load.
PF = P / S
Harmonic current adds RMS loading without useful active power in this sinusoidal-voltage model. A capacitor does not remove it.
Ploss = 3I²R
Lower upstream current reduces resistive losses in the corrected segment. Active load energy is otherwise unchanged.
Calculation basis, tariff formulas & references
Balanced three-phase load, fixed sinusoidal line voltage, lagging displacement PF and constant active load are assumed. This is an engineering estimate, not a stamped design or an IEEE 519 / NEC compliance assessment.
Capacitor compensation Qc = P[tan(acos(PF1)) - tan(acos(PF2))]. The peak-duty bank is scaled by peak kW / operating kW; it requires automatic steps at lower load. kVAR is reactive-power rating, not capacitance in microfarads.
Advanced mode uses true PF = displacement PF / sqrt(1 + THDi^2) for the initial state. After correction, harmonic amperes remain constant unless the AHF scenario is enabled. Residual THDi is referenced to the corrected fundamental current.
AHF sizing assumes proportional reduction of the harmonic spectrum and simultaneous worst-case peak load. The allowance is user-selected, not a code requirement. The AHF is allocated to harmonic filtering; fundamental VARs are supplied by the capacitor bank. Confirm spectra, neutral current, phase imbalance, voltage, duty and manufacturer derating.
IEEE 519 evaluates harmonic performance at the point of common coupling using voltage distortion, individual harmonic limits and current TDD with system short-circuit information. THDi alone cannot demonstrate compliance. NEC requirements for installation, ratings and protection require a separate design review.
Feeder losses = 3 I_RMS^2 R. R is the operating-temperature resistance of one phase in only the corrected, customer-metered upstream segment. Harmonic-frequency resistance changes, neutral current, transformer core/eddy losses and voltage drop are excluded. Banks at the service entrance do not reduce losses in downstream uncorrected feeders.
Operating kW is downstream useful load; modeled feeder losses are added once to the energy bill. Demand uses the separately entered peak and selected meter PF basis. The same peak/PF and rates repeat for 12 months, with no demand ratchet or minimum billing demand. Demand effects of feeder and correction-device active losses are excluded.
Monthly bill includes modeled demand, load energy, feeder losses, correction-device energy and entered fixed charges; taxes and unentered charges are excluded. Annual net savings subtract device energy and added maintenance. Simple payback and annual return exclude financing, incentives and time value of money.
Released kVA is the arithmetic peak apparent-load reduction, not an authorization to add load. Transformer harmonic derating, ambient temperature, cooling and protection may constrain usable capacity. Resonance order uses transformer impedance only and an infinite upstream source; use a complete harmonic study for selection.
Sources: Eaton plant-engineer PF guide · Eaton harmonic resonance guidance. Harmonic compliance and installation requirements must be checked against the applicable IEEE 519 and NEC editions.