Capacitor Bank

A capacitor bank is an assembly of capacitor units connected to supply reactive power to the electrical system. Its main purpose is to support voltage, reduce reactive-power demand from upstream sources, and improve power factor in transmission, distribution, or industrial networks.

Capacitor banks are attractive because they are relatively simple, efficient, and low cost compared with many dynamic reactive-power devices. Their limitation is that their reactive output depends on system voltage, so they are least effective precisely when voltage has already fallen significantly.

Key Aspects of Capacitor Banks:

• Reactive-Power Supply: Capacitor banks inject reactive power locally, which helps support voltage and reduces the reactive burden seen by lines, transformers, and generators. This can lower losses and free capacity for active-power transfer.
• Voltage Dependence: Capacitor reactive output changes with the square of voltage. If voltage drops, the bank provides less reactive support, which is why it is useful but not always sufficient for fast dynamic voltage problems.
• Stepwise Control: Many installations use switched capacitor steps so reactive support can be increased or reduced in discrete blocks. This provides practical coarse control but not the smooth response of a fully dynamic compensator.
• Common Locations: Capacitor banks are widely used in distribution substations, industrial plants, and some transmission applications. The choice of location strongly affects how much they improve local voltage and upstream reactive loading.
• Operational Risks: Switching transients, harmonic resonance, and overvoltage must be considered when applying capacitor banks. Proper switching strategy and harmonic assessment are important parts of sound design.