Understanding Power Factor Correction (PFC)

In commercial and industrial electrical systems, motors, transformers, and fluorescent lighting require a magnetic field to operate. Creating this magnetic field draws Reactive Power (kVAR). This reactive power does no actual "work", but it still takes up space in the cables and transformers, forcing the system to draw more total current from the grid.

The Beer Analogy

The easiest way to understand Power Factor is a pint of beer:

• Real Power (kW): The actual liquid beer. This is what you want and what does the actual work.
• Reactive Power (kVAR): The froth at the top. It takes up space in the glass but doesn't quench your thirst.
• Apparent Power (kVA): The total glass. The electricity provider has to supply the entire glass, froth and all.

The Power Factor is the ratio of liquid to the total glass. A Power Factor of 1.0 is a perfect pint with no froth. A Power Factor of 0.65 means your glass is 35% froth—you are paying for capacity you aren't using.

Why Install Capacitor Banks?

By installing Power Factor Correction (PFC) capacitors, you supply the reactive power (the froth) locally at your switchboard. This means the utility company no longer has to supply it through the incoming cables. The benefits are massive:

• Avoid Reactive Power Penalties: Most commercial energy tariffs will severely fine businesses if their Power Factor drops below 0.95.
• Free Up Transformer Capacity: As you can see in the calculator above, correcting your power factor directly drops your kVA demand. This allows you to add more machinery or electrical loads to a factory without having to pay the DNO for an expensive transformer upgrade.
• Reduce Cable Heating & Voltage Drop: By reducing the total Amps flowing through the cables, I²R losses (heat) decrease, improving the lifespan of switchgear and reducing voltage drop across the site.

The Calculation Formula

This TMUK tool calculates the required capacitor size using standard trigonometry: