Why is POWER FACTOR CORRECTION important for electric utility bills?
The main contributor to a low power factor is normally motor loads, which may include:
- Heating and cooling equipment
- Pumps and fans
- Industrial machinery
In residential buildings, these types of loads are minimal, so residential electric rates typically ignore the power factor. However, this is not the case for commercial and industrial consumers. Normally, the minimum power factor is defined by the electric utility company.
- A minimum power factor may be required, for example, 90%.
- Alternatively, the reactive power (kVAR) may be capped in the function of real power (kW). For example, an electric company might bill consumers whose reactive power exceeds 40% or real power (this would correspond to power factors below 92.85%).
In either billing approach, the fee paid by the consumer increases as the power factor decreases – the bill may rise considerably in the case of large industrial consumers.
Improving the power factor using NRG Savers custom-built capacitor banks is extremely valuable to the consumer. It’s perhaps the most efficient way to clean up your power in your facility and increase your voltage while decreasing the harmonics through your facility.
How is power factor corrected?
The basic principle of power factor correction is to make inductive and capacitive loads balance each other. For instance, a motor (resistive-inductive load) drawing 10 kVAR of reactive power and a capacitor (capacitive load) rated at 8 kVAR will only draw a net reactive power of 2 kVAR. This is the reason why electric utility customers install capacitor banks to correct the power factor. The adequate kVAR rating of the capacitor bank will depend on the load and the billing method.
Power Factor Correction: Minimum Value Requirement
In this scenario, it is simply a matter of calculating the actual power factor, and the kVAR difference that would be required to drive it above the minimum. For instance, consider the following inductive load:
- P = 100 kW
- Q = 70 kVAR
- S = 122 kVA
- PF = 100kW / 122 kVA = 0.8192 (81.92%)
If a minimum of 90% was required, apparent power would need to be:
- S = P / 0.90 = 100 kW / 0.90 = 111.11 kVA
- Q = 48.43 kVAR
This means that the capacitor bank must have a minimum capacity of:
- Q (capacitor) = 70 kVAR – 48.43 kVAR = 21.57 kVAR
Power Factor Correction: Percentage of Real Power Cap
The calculation is much simpler in this scenario. Consider the same example and a reactive power cap of 40% of real power.
- Q (max) = 100 kW x 40% = 40 kVAR
- Q (actual) = 70 kVAR
- Q (capacitor) = 70 kVAR – 40 kVAR = 30 kVAR
Capacitors are normally oversized by a slight margin, in order to exceed the minimum requirements of electric utility companies.
Strictly speaking, power factor correction is not an energy-saving measure (real power remains the same). However, it is a cash-saving measure. Given that one of the main purposes of energy efficiency is to save money, power factor correction is typically carried out along with energy efficiency retrofits. There are slight energy savings through the reduction of line currents, but the effect tends to be negligible compared with eliminating the power factor fee from the electric bill.
Power factor is likely to be an issue in buildings with considerable motor loads, especially very dated buildings where motors may be old models with a low power factor.