What is power factor correction (PFC)?
Power Factor Correction is the process of adding capacitors to an electrical system to eliminate waste. Equipment like motors introduces reactive power, which does no useful work but raises your billed maximum demand (kVA). PFC cancels that reactive power, so you pay only for the useful power (kW) you consume: lower demand charges, more capacity, and no power-factor penalties.
- Power factor is the ratio of useful power (kW) to total power supplied (kVA).
- Motors and transformers add reactive power, which raises billed maximum demand (kVA).
- PFC adds capacitors to cancel that reactive power, cutting demand charges and freeing capacity.
- In South Africa, tariffs penalise a power factor below about 0.90 to 0.92; correction removes the penalty.
Power factor is a fundamental measure of how effectively electrical power is converted into useful work. It is the ratio of Real Power (kW), the useful power, to Apparent Power (kVA), the total power supplied. The goal is a power factor as close to 1 (unity) as possible, yet most commercial and industrial sites run below it, sometimes as low as 0.6.
The mechanics: how PFC works
Power factor correction strategically adds capacitors to an electrical system. It counters the inefficiency caused by common industrial devices such as electric motors and transformers, which introduce reactive power. Reactive power does no useful work itself; it circulates, raising the total apparent power (kVA) and lowering the power factor.
By introducing capacitive reactive power, PFC counteracts the inductive reactive power from equipment, managing the total flow of power, reducing kVA, and improving overall efficiency.
The business case: benefits of improved power factor
- Cost savings: on a demand-based tariff, a better power factor cuts billed maximum demand (kVA), lowering the utility bill directly.
- Increased capacity: a better power factor uses existing infrastructure more efficiently, freeing capacity on transformers and cables.
- Better equipment life: PFC reduces the current burden on transformers and motors, promoting longer life and improved reliability.
Municipal and Eskom tariffs apply penalties, often a charge multiplier, when a customer's power factor drops below a set threshold, typically 0.90 or 0.92. Correction to between 0.98 and 0.99 eliminates those penalty charges entirely.
The path to optimal PFC
Getting PFC right is a measured process, not a one-off purchase: survey the site, confirm the financial case, size the system to the load, install it, verify the corrected power factor, then monitor it so correction stays effective as the load changes.
What is power factor?
It is a measure of how effectively electrical power is converted into useful work, expressed as the ratio of Real Power (kW) to Apparent Power (kVA). The goal is a power factor as close to 1 (unity) as possible; many sites run as low as 0.6.
How does power factor correction save money?
On a demand-based tariff, improving power factor reduces the site's billed maximum demand (kVA), which lowers the utility bill directly. It also frees capacity on transformers and cables and reduces stress on equipment.
What power factor penalty applies in South Africa?
Municipal and Eskom tariffs apply penalties, often a charge multiplier, when power factor drops below a set threshold, typically 0.90 or 0.92. Correction to around 0.98 to 0.99 removes those penalties entirely.
What causes a poor power factor?
Inductive equipment such as electric motors, transformers and refrigeration compressors draws reactive power to sustain magnetic fields. That reactive power raises apparent power (kVA) without doing useful work, lowering the power factor.