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Capacitor power at different voltage

V
Hz
V
Hz
Description

Capacitor Power at Different Voltage

In certain power networks, a significant difference may exist between the rated voltage and the service voltage. For example, a capacitor rated at 400 V may be used in a 380 V system. In such cases, the actual reactive power output of the capacitor varies with voltage and frequency. This tool calculates the real reactive power delivered by a capacitor under non-rated conditions.

Application Scenarios

  • Industrial substation reactive power compensation
  • Capacitor bank selection verification
  • System voltage fluctuation analysis
  • Capacitor lifespan evaluation (overvoltage/undervoltage)

Parameter Description

Parameter Description
Input Voltage Actual operating voltage of the network (e.g., 380V, 400V), unit: Volts (V)
Supply Frequency Operating frequency of the network (e.g., 50 Hz or 60 Hz), unit: Hertz (Hz)
Capacitor Rated Power Nominal reactive power rating of the capacitor, unit: kVAR
Capacitor Rated Voltage Rated voltage specified on the capacitor nameplate, unit: Volts (V)
Capacitor Rated Frequency Design frequency of the capacitor, typically 50 Hz or 60 Hz

Calculation Principle

The reactive power output of a capacitor is proportional to the square of the applied voltage:

Q_actual = Q_rated × (U_in / U_rated)² × (f_supply / f_rated)

Where:
- Q_actual: Actual reactive power output (kVAR)
- Q_rated: Rated reactive power of the capacitor (kVAR)
- U_in: Input voltage (V)
- U_rated: Rated voltage of the capacitor (V)
- f_supply: Supply frequency (Hz)
- f_rated: Rated frequency of the capacitor (Hz)

A 10% increase in voltage results in approximately 21% higher reactive power (due to quadratic relationship)
Overvoltage can cause overheating, insulation breakdown, or reduced lifespan

Usage Recommendations

  • Avoid long-term operation above the capacitor's rated voltage
  • Select capacitors with slightly higher rated voltage than system voltage (e.g., 400V for 380V systems)
  • Use step-by-step switching in multi-level capacitor banks to prevent overcompensation
  • Combine with power factor controllers for dynamic reactive power management

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