Qr = Qc * (U_in / Uc)² * (f_in / fc)
Qc = Qr * (Uc / U_in)² * (fc / f_in)
Qr = Capacitor power at different voltage (kVAr)
Qc = Capacitor power (kVAr)
U_in = In voltage (V)
Uc = Capacitor voltage (V)
f_in = Supply frequency (Hz)
fc = Capacitor frequency (Hz)
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.
1. Industrial substation reactive power compensation
2. Capacitor bank selection verification
3. System voltage fluctuation analysis
4. Capacitor lifespan evaluation (overvoltage/undervoltage)
| 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 |
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
1. Avoid long-term operation above the capacitor's rated voltage
2. Select capacitors with slightly higher rated voltage than system voltage (e.g., 400V for 380V systems)
3. Use step-by-step switching in multi-level capacitor banks to prevent overcompensation
4. Combine with power factor controllers for dynamic reactive power management
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