Power Factor
The ratio of real power (kW) to apparent power (kVA) indicating how effectively electrical power is utilized.
Power factor = kW/kVA = cos(phi). PF 1.0 (unity) means all current produces work. Lagging PF (inductive loads) indicates reactive power consumption. Low PF means increased current, larger equipment needed, higher losses, utility penalties.
Correction using capacitor banks improves toward unity. Harmonics create displacement vs. true power factor differences.
QDTB specifies parameters for expected load PF and supplies capacitor banks for correction.
Related Products
Related Terms
Apparent Power (kVA)
The total power in an AC circuit combining real (active) and reactive power, measured in kilovolt-amperes (kVA).
kVA Rating
The apparent power rating of a transformer in kilovolt-amperes, determining load-carrying capacity.
Harmonics
Integer multiples of fundamental frequency from non-linear loads, causing increased transformer losses and overheating.
More Terms Starting with “P”
Power Transformer
A large transformer (>10 MVA) used in transmission networks for stepping voltage between system levels.
Partial Discharge (PD)
Localized electrical discharges in small insulation regions not bridging electrodes, indicating defects or aging.
Prefabricated Substation
A factory-assembled complete substation integrating transformer, switchgear, and protection for rapid installation.
Phasor Diagram
A graphical representation of AC voltage and current relationships in a transformer showing magnitude and phase angle.
More in “Electrical Fundamentals”
Apparent Power (kVA)
The total power in an AC circuit combining real (active) and reactive power, measured in kilovolt-amperes (kVA).
Eddy Current
Circulating currents induced in conductive materials by changing magnetic fields, causing energy losses in transformers.
EMF (Electromotive Force)
The voltage generated by electromagnetic induction in a transformer winding, proportional to flux change and turns.
Frequently Asked Questions
How do I calculate power factor?
Power factor = real power (kW) / apparent power (kVA), which for a sinusoidal load equals cos φ, the cosine of the angle between voltage and current. A plant drawing 800 kW at 1,000 kVA therefore runs at 0.80 PF. Where harmonics are present, also check true power factor, which accounts for distortion as well as displacement.
What causes a low power factor?
Inductive loads — induction motors, transformers, ballasts and lightly loaded drives — draw magnetising current that produces no useful work, so the current lags the voltage and PF falls. Plants that run motors at part load all day commonly sit between 0.70 and 0.85.
How is a low power factor corrected?
By supplying reactive power locally, normally with capacitor banks (fixed or automatically switched), detuned reactors, or active filters where harmonics are present. Correction reduces line current, cable and transformer losses, releases capacity and avoids utility low-PF penalties.
Need help with transformer selection?
QDTB engineers can help you choose the right equipment based on your specific requirements