Selection Principles for High-Voltage or Low-Voltage Capacitors for Power Factor Correction in Industrial Power Systems
Technical Support
Both low-voltage and high-voltage capacitors can improve power factor (PF), reduce electricity costs, and ease the load on equipment. Low-voltage capacitors also help reduce line losses between the power supply and the load side.
With proper control, high-voltage capacitors can be easily monitored and used to improve the power factor of the entire plant. Their investment cost is lower compared to low-voltage capacitors. Additionally, power losses of high-voltage capacitors are typically only about 20% of those of low-voltage capacitors, which also impacts electricity costs. If harmonics exist in the power system, using high-voltage capacitors can localize power factor correction to a single point, reducing the risk of harmonic-related problems.
If the voltage applied to capacitors exceeds their rated voltage during use, it can shorten their lifespan. Therefore, it is essential to ensure that the applied voltage does not exceed the maximum rated operating voltage.
If the current flowing into the capacitor exceeds its maximum allowable rated current, its lifespan will also be shortened. It is necessary to monitor the operating current to avoid exceeding this limit. Excessive current is often caused by harmonic currents (Ih) flowing into the capacitor.
Countermeasure: Install series reactors or harmonic filters at appropriate locations. When implementing such measures, discussions with manufacturers, accurate measurements, and careful planning are recommended.
When using capacitors with series reactors, special attention must be paid to the selection of the capacitor’s rated voltage.
| Series Reactor in Capacitor Circuit |
The voltage between capacitor terminals is higher than the power supply voltage |
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| 6% |
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| 8% |
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| 13% |
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Calculation Examples
High-Voltage Calculation Example
Assume a system voltage of 22.8 kV and a required capacitor capacity of 200 kVAR.
To account for harmonics or voltage rise caused by a series reactor, the capacitor rated voltage is increased to 25.4 kV.
Required capacity becomes
：
200 × 1.241 (value from table) = 248.2 kVAR
Formula：
Low-Voltage Calculation Example
Original capacitor rating: 380V, 50 kVAR
After increasing the rated voltage to 440V, the required capacity becomes ：
50 × 1.341 (value from table) = 67 kVAR
Formula：
