Power Factor Capacitor Bank

Overview

Inductive loads, motors, transformers, welding sets, draw reactive power that does no useful work but loads the cables and the supply transformer, and that the utility bills for through a poor power factor. A power-factor capacitor bank supplies that reactive power locally, close to the loads, so the upstream network only has to carry the real current. This 250 kVAr bank is automatic and detuned: it switches capacitance in five steps to track the plant's changing reactive demand, and each step is fitted with a series reactor so the bank cannot resonate with harmonics on a modern, electronics-heavy supply.

How it works

The reactive power comes from the Capacitor Power Stage, a set of five Capacitor Step groups, each a three-phase cluster of dry Power Capacitor units forming one 50 kVAr increment. When a step is switched off, its Discharge Resistor bleeds the stored charge down to a safe voltage before anyone could touch the terminals.

Steps are connected and disconnected by the Step Switching stage. Capacitors draw a violent inrush current at the instant of connection, so each step uses a Capacitor-Duty Contactor with pre-charge contacts and an inrush resistor, and is protected against faults by HRC HRC Fuse cartridges. In series with every step sits a Detuning Reactor tuned below the lowest troublesome harmonic, which keeps the capacitors from amplifying harmonic currents.

A Power-Factor Controller is the brain: it measures the line current through its current transformer, computes the running power factor, and switches steps in or out to hold the target. Its display shows the present power factor and which steps are active. Power is distributed across the steps on a Copper Busbar, and the Cooling System fans hold the capacitor compartment within its temperature rating. Everything is built into the vented Enclosure.