Power Factor: Read It Off a Real Bill

10 min · difficulty 5/10

Pull up a commercial demand bill and you might find a line like this: real demand 100 kW, billed demand 125 kVA, power factor 0.80, PF adjustment applied. The plant only did 100 kW of useful work, but the utility billed it for 125 kVA and tacked on a penalty. Before reading on, work out the power factor yourself and decide whether this customer is really being penalized for something real, or just nickel-and-dimed.

The number falls right out of the bill. Power factor is real power divided by apparent power, kW over kVA, and 100 divided by 125 is 0.80. That is the same 0.80 you would get from the cosine of the power-triangle angle. A perfect load would show 1.00, where every kVA delivered turns into a kW of work. At 0.80 the plant is pulling 25 percent more apparent power than the work it performs.

That gap is not a paperwork fee. Apparent power sets the current, so a 0.80 PF load draws 125 kVA worth of current to do 100 kW of work. The extra reactive current still flows through every transformer and conductor between the meter and the substation, heating them and burning real energy as I-squared-R loss the kWh meter never records. The utility bills for kVA, or adds a PF penalty, to recover the delivery cost the kWh charge misses.

The fix lives at the customer’s own plant. Most low-PF load is inductive, motors and transformers pulling lagging reactive power, and a shunt capacitor bank supplies that reactive power locally. The inductive load now draws its VARs from the capacitor instead of dragging them down the feeder, so line current and billed kVA both drop while the 100 kW of real work stays exactly the same.

Power factor correction with a capacitor Two power triangles drawn to the same scale. The before triangle has real power 100 kW, reactive power 75 kVAR, and apparent power 125 kVA, for a power factor of 100 divided by 125 equals 0.80. The after triangle keeps real power at 100 kW but the reactive leg has shrunk to 32 kVAR, giving apparent power 105 kVA and a power factor of 100 divided by 105 equals 0.95. A capacitor supplies about 43 kVAR locally, so the line delivers fewer reactive amps and the angle closes up. Correcting power factor with a capacitor same 100 kW load, fewer reactive amps from the line Before PF = 100 / 125 = 0.80 100 kW 75 kVAR 125 kVA add capacitor After PF = 100 / 105 = 0.95 100 kW 32 kVAR 105 kVA The capacitor supplies about 43 kVAR locally, so the load pulls its VARs from the cap, not the line. The reactive leg falls 75 to 32 kVAR, the angle closes up, and line current drops.
A capacitor supplies reactive power locally, shrinking the reactive leg from 75 to 32 kVAR. The same 100 kW load goes from 125 kVA at 0.80 power factor to 105 kVA at 0.95, cutting line current.

Run the same plant after correction and the meter tells the story: still 100 kW of real demand, but now only 105 kVA. Divide and the power factor is about 0.95, comfortably above most penalty thresholds, so the PF adjustment disappears. A capacitor adds no real power, it only supplies the reactive power the load was forcing the line to carry, which is why the same work now costs the utility, and the customer, far less to deliver.

Power factor penalties, reactive charges, and %Z mismatches show up as real line items on a utility bill or a bid rejection. DistroForge Insider applies these fundamentals to pricing and equipment-selection intelligence.

Question 1 of 4

A commercial bill shows real demand 100 kW and billed demand 125 kVA. What is the power factor? (PF = kW divided by kVA)

Educational material only. This is not engineering, safety, or procurement advice. Confirm any value against manufacturer documentation and a licensed professional before specifying equipment.