Inputs
Example Data
| Item | Example Value | Unit | Why it matters |
|---|---|---|---|
| Max demand | 120 | kW | Higher demand increases kVA exposure. |
| Actual PF | 0.82 | — | Low PF raises current and apparent power. |
| Target PF | 0.90 | — | Penalty begins below this threshold. |
| Energy | 45,000 | kWh | Base energy cost for the period. |
| Energy rate | 38 | per kWh | Used to estimate energy charges. |
| Demand rate | 950 | per kVA | Used to price demand and penalty. |
Formula Used
- kVA = kW ÷ PF
- Target kVA = kW ÷ Target PF
- Extra kVA = max(0, Actual kVA − Target kVA)
- Penalty = Extra kVA × Demand Rate (per kVA)
- Points = max(0, (Target PF − Actual PF) ÷ 0.01)
- Base = Energy Cost + Demand Cost + Fixed Charges
- Penalty = Base × (Points × Surcharge% per point)
Article
Power factor (PF) is a measure of how effectively electrical power is being converted into useful work. On construction sites, heavy motors, welders, hoists, temporary chillers, and poorly loaded transformers often pull reactive power that does not create productive output. Utilities still need to supply that reactive component, so many tariffs apply a penalty when PF falls below a threshold. Understanding the likely penalty before you receive the monthly bill helps you defend project budgets, evaluate corrective equipment, and avoid surprises during peak activity.
This calculator estimates PF-related costs using two common billing styles. The kVA adjustment approach treats low PF as extra billed apparent power. You enter demand and PF, and the tool converts demand into kVA at both the actual PF and a target PF. The difference (extra kVA) is multiplied by the demand rate. The surcharge per PF point approach applies a percentage uplift for each 0.01 PF below the threshold, using a base made up of energy cost, demand cost, and fixed charges.
Example data illustrates how quickly costs can rise. Assume a temporary substation records 120 kW maximum demand at an actual PF of 0.82, with a target PF of 0.90. The period energy is 45,000 kWh, the energy rate is 38 per kWh, and the demand rate is 950 per kVA. Even if energy consumption stays the same, low PF increases apparent power, which can inflate the demand portion of the bill and add a direct penalty, depending on the tariff.
Beyond cost forecasting, PF correction can reduce cable heating, stabilize voltage, and free transformer capacity. The capacitor sizing estimate (kVAr) provides a starting value based on the difference between the tangent of the phase angles at the actual and target PF. Treat this as an engineering estimate: final sizing should consider load variation, harmonic content from variable-speed drives, switching steps, and the utility’s measurement method.
For best results, use measured PF from a power quality meter or the utility bill, and use the same billing period used for demand charges. If your tariff defines a different base for surcharges, update the method settings until the calculator matches one known invoice, then reuse it for future months and scenarios.
FAQs
1. What does PF penalty mean on a construction power bill?
A PF penalty is an extra charge applied when measured power factor falls below a utility threshold. It compensates for additional current and reactive power the network must supply to your temporary or permanent connection.
2. Which method should I choose in this calculator?
Use kVA adjustment if your bill shows billed kVA or maximum kVA demand. Use surcharge per PF point if your bill applies a percentage add-on for each 0.01 PF below the target.
3. Can I enter demand in kVA instead of kW?
Yes. Select kVA as the demand input type. The tool estimates kW using the actual PF, then completes all calculations. If you know kW directly, enter kW for the most accurate result.
4. Why is the capacitor kVAr result only an estimate?
It assumes steady demand and ideal sinusoidal conditions. Real sites have varying loads, switching events, and harmonics. Use the estimate to shortlist equipment, then confirm with a qualified electrical engineer and measurements.
5. Will improving PF reduce my energy (kWh) charges?
Usually, PF correction mainly reduces demand-related charges and penalties. kWh depends on real energy used by equipment. However, better PF can reduce losses in cables and transformers, which may slightly improve efficiency.
6. What PF target should I use?
Use your tariff threshold, commonly 0.90 or 0.95. If you are planning correction, set the target slightly above the threshold to provide margin for load changes during peak construction activities.
7. How do I validate the calculator against my bill?
Enter one historical billing period using known demand, PF, and rates. Adjust the method and surcharge setting until the estimate matches that invoice. Then keep the same settings for forecasting future months.
How to Use
- Pick a method that matches your utility bill format.
- Enter max demand and the measured power factor.
- Add energy use, rates, and any fixed charges.
- Click Calculate to show penalty and totals.
- Use the capacitor estimate to plan PF correction.
- Download CSV or PDF for project documentation.