# 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).

> Canonical page: https://elysiatools.com/en/tools/capacitor-reactive-power

- **Category:** Math & Numbers

- **Keywords:** capacitor, reactive power, Q_c, 2πfCU², capacitive reactance, X_c, three-phase, star, delta, power systems, electrical engineering

## 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.

## Inputs

- **Connection** (select)
- **Capacitance C** (number): Capacitance value in the selected unit. For three-phase, enter the per-phase capacitance.
- **Capacitance Unit** (select)
- **Frequency f (Hz)** (number): e.g. 50
- **Voltage U (V)** (number): For single-phase: phase voltage. For three-phase star/delta: line-to-line voltage.
- **Decimal Places** (number)

## 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

- Select the electrical connection type: single-phase, three-phase star (Y), or three-phase delta (Δ).
- Enter the capacitance value per phase (in Farads or Microfarads), the system frequency in Hertz, and the operating voltage.
- Click 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.

## Frequently asked questions

### 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.

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