Power Factor Correction?
Most loads employed in industry such as induction motors, transformers, light ballasts and induction heating furnaces are predominantly inductive. Such loads draw two kinds of power:
- Active power (kW) to perform work
- Reactive power (kVAr) to build the magnetic field.
The active and reactive power make up the total power – apparent power measured in kVA. Reactive power is considered as wasted energy as it does not contribute to useful work. The relationship between the three power quantities can be explained using the power triangle as shown in Figure 1.
Figure 1: Power Triangle
The power triangle illustrates that for a given active power rating (kW) a higher apparent power (kVA) need to be supplied. This means that more current is drawn from the utility to supply the reactive power (kVAr).
The ratio of active power to the apparent power is known as the power factor (cos φ).
What are the implications of low power factor?
An electrical installation with low power factor means that the apparent power (kVA) drawn is considerably larger than the active power (kW) needed for the loads to do work. For example with a power factor of 0.65, a system would need to draw almost 154kVA to produce 100kW whereas for a system with a power factor of 0.95, it would need 105kVA to produce the same active power. This has a huge implication on the electricity bills as will be explained hereunder.
Why should one invest in a power factor correction equipment?
As concerns the consumer, the simple answer is to save on utility bills. In Malta, for non-residential sites one can choose between 2 tariffs; Non-Residential kWh and Non-Residential kVA. Table 1 and 2 show the cost per unit consumed for different bands for the kWh and kVAh tariffs (2015).
Table 1: Non-Residential kWh tariffs
Table 2: Non-Residential kVAh tariffs
As shown in the Tables, for non-residential premises with a low power factor the sensible option would be to opt for the kWh tariff. This might look strange at first sight as kWh tariff is more expensive than the kVAh tariff, however metered kVAh units will be much more as exemplified above.
On the other hand, for non-residential premises with a high power factor the most advantageous tariff is the kVAh tariff as with a high power factor, the kVAh will be close or equal to the kWh consumed. Of course this depends on the level of power factor correction installed.
The following results are from a case study conducted in Malta on a company with an average consumption of 280 units per hour and a power factor of 0.7. The company was being charged using the most advantageous tariff for low power factor scenarios, i.e. the kWh tariff. After installing a power factor correction equipment to improve the power factor from 0.7 to 0.99 and changing the tariff to kVAh the annual utility bill dropped by nearly €35,000.
If you want to know more on how you can benefit from savings on your utility bills, we encourage you to contact us.