Power Factor

Power Factor (PF)

In AC circuits, the Power Factor (PF) is the ratio of the real power. That is use to do work and the apparent power that is supplied to the circuit.

The power factor can get values in the range from 0 to 1.

When all the power is reactive power with no real power (usually inductive load) – the power factor is 0.

When all the power is real power with no reactive power (resistive load) – the power factor is 1.

In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred.

The higher currents increase the energy lost in the distribution system, and require larger wires and other equipment. Because of the costs of larger equipment and wasted energy, electrical utilities will usually charge a higher cost to industrial or commercial customers where there is a low power factor.

How to calculate power factor

To calculate power factor, you need a power quality analyzer or power analyzer that measures both working power (kW) and apparent power (kVA), and to calculate the ratio of kW/kVA.

The power factor formula can be express in other ways:

PF = (True power)/(Apparent power)



Where watts measure useful power while VA measures supplied power. The ratio of the two is essentially useful power to supplied power.

Power factor

As this diagram demonstrates, power factor compares the real power being consume to the apparent power, or demand of the load. The power available to perform work is call real power. You can avoid power factor penalties by correcting for power factor.

Poor power factor means that you’re using power inefficiently. This matters to companies because it can result in:

  • Heat damage to insulation and other circuit components
  • Reduction in the amount of available useful power
  • A required increase in conductor and equipment sizes

Finally, power factor increases the overall cost of a power distribution system because the lower power factor requires a higher current to supply the loads.

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