Power Factor Correction
Prerequisites
A factory draws 1,000 kVA from the grid but only 700 kW does useful work. The other 714 kVAR sloshes back and forth as reactive power, heating cables and occupying grid capacity without producing anything. The utility must size its transformers and wires for the full 1,000 kVA. Who pays for the wasted capacity?
Power factor is the ratio of real power (kW) to apparent power (kVA). A power factor of 0.70 means only 70% of the current drawn actually does work. Motors, fluorescent lighting, and inductive loads are the primary culprits, drawing current that lags behind voltage and creating reactive power demand. The grid must supply this current even though it performs no useful function at the customer's site.
Calculate the wasted capacity. At power factor 0.70, delivering 700 kW requires 1,000 kVA of apparent power: I = 1,000 kVA / 480 V = 2,083 A. At power factor 0.95, delivering the same 700 kW requires only 737 kVA: I = 1,537 A. That is 26% less current for the same useful work.
How can a customer improve power factor without changing their equipment?
Capacitor banks. Capacitors supply reactive power locally, offsetting the reactive demand from inductive loads. Installing capacitor banks at the factory reduces the reactive current flowing through utility lines. The utility sees higher power factor; its wires and transformers serve more real power with the same capacity. Utilities enforce this through power factor penalties: charges for customers below 0.85-0.90.
A factory has a power factor of 0.70, meaning it draws 1,000 kVA to deliver 700 kW of useful power. The remaining 714 kVAR of reactive power:
Reactive power flows back and forth between source and load, contributing to current magnitude but not to useful work. The utility must size all its equipment (wires, transformers) for the total apparent power, not just the real power.
The answer is DLesson complete
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