Capacitor Reactive Power Calculator (Q_c = 2πfCU²)
Compute the reactive power produced by a known capacitor: Q_c = 2π·f·C·U². Supports single-phase, three-phase star (Y) and delta (Δ) connections. Returns Q_c in var/kvar, capacitive reactance Xc, and capacitor current Ic. Complementary to the power-factor-correction tool (which sizes a capacitor for a target cosφ).
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Key facts
Category
Math & Numbers
Input types
select, number
Output type
json
Sample coverage
4
API ready
Yes
Overview
Calculate the reactive power, capacitive reactance, and current of a capacitor using the standard formula Q_c = 2πfCU². This calculator supports single-phase, three-phase star (Y), and three-phase delta (Δ) connections, providing precise electrical engineering calculations for power systems.
When to use
When verifying the actual reactive power output of an existing capacitor bank under specific operating voltage and frequency conditions.
When calculating the capacitive reactance and current of a capacitor to ensure proper sizing of fuses, cables, and switchgear.
When analyzing three-phase power factor correction systems configured in either star (Y) or delta (Δ) topologies.
How it works
1Select the electrical connection type: single-phase, three-phase star (Y), or three-phase delta (Δ).
2Enter the capacitance value per phase (in Farads or Microfarads), the system frequency in Hertz, and the operating voltage.
3Click calculate to compute the capacitive reactance, phase current, and total reactive power in var and kvar.
Use cases
Determining the reactive power output of a legacy capacitor bank when relocated to a grid with a different voltage or frequency.
Calculating the current draw of a capacitor to select appropriate overcurrent protection devices.
Verifying the impedance and reactive power contribution of individual capacitor steps in an automatic power factor correction panel.
Examples
1. Single-Phase Capacitor Analysis
Electrical Maintenance Engineer
Background
An engineer needs to verify the current and reactive power of a 10 µF motor run capacitor operating on a 230 V, 50 Hz single-phase supply.
Problem
Manually calculating the capacitive reactance and current is time-consuming and prone to rounding errors.
How to use
Select 'Single phase' connection, enter 10 for capacitance, select 'µF', enter 50 for frequency, and 230 for voltage.
Outcome
The tool outputs a capacitive reactance of 318.3099 Ω, a current of 0.7226 A, and a reactive power of 166.1903 var.
2. Three-Phase Delta Capacitor Bank Verification
Power Quality Consultant
Background
A consultant is inspecting an industrial facility's power factor correction panel containing delta-connected capacitor steps of 50 µF per phase at 400 V, 50 Hz.
Problem
The consultant needs to determine the total kvar output of the step to verify if it matches the nameplate rating.
How to use
Select 'Three-phase Delta (Δ)' connection, enter 50 for capacitance, select 'µF', enter 50 for frequency, and 400 for voltage.
FAQ
What formula is used to calculate the reactive power?
The calculator uses Q_c = 2πfCU² for single-phase, Q_c = 3·2πfC(U_LL/√3)² for three-phase star, and Q_c = 3·2πfCU_LL² for three-phase delta.
What is the difference between line-to-line and phase voltage in this calculator?
For single-phase connections, enter the phase voltage. For three-phase star or delta connections, enter the line-to-line voltage.
Can I input capacitance in microfarads (µF)?
Yes, the calculator supports both Farads (F) and Microfarads (µF) as input units.
How does connection type affect the reactive power output?
A delta connection produces three times more reactive power than a star connection for the same per-phase capacitance and line-to-line voltage.
Does this tool calculate the required capacitance for a target power factor?
No, this tool calculates the output of a known capacitor. Use a power factor correction tool to size a capacitor for a target cosφ.