Power factor is an expression of energy efficiency. It is the ratio of working power measured in kilowatts (kW) to apparent power measured in kilovolt amperes (KVA). Apparent power is also known as demand. It is the measure of the amount of power used to run machinery and equipment during a certain period. Power factor is a dimensionless number in the closed interval of -1 to 1.

Power Factor = True power (KW)/Apparent power (KVA)

1. A machin runs at 100 kW (Working Power) and the Apparent Power meter records 125 kVA. To find the PF, divide 100 kW by 125 kVA to yield a PF of 80%. This means that only 80% of the incoming current does useful work and 20% is wasted through heating up the conductors.

. The “ideal” power factor is one. This is when there is no reactive power through the circuit, and hence apparent power (kVA) is equal to real power (kW).

. A load with a power factor of 1 is the most efficient loading of the supply.

. low PF indicates poor utilization of electrical power.

Reasons for low power factor

1. Inductive loading – 90% of the industrial load consists of induction machines (single and three phase). Such machines draw magnetizing current to produce the magnetic field and hence work at low power factor.
2. Variations in power loading – When the system is loaded lightly, the voltage increases and the current drawn by the machines also increases. This results in a low power factor.
3. Harmonic currents – Harmonic currents, generated by non-linear electronic loads, increase power system heat losses and power bills of end-users. These harmonic-related losses reduce system efficiency, cause apparatus overheating.

Why improve it?

Improving the PF can maximize current-carrying capacity, improve voltage to equipment, reduce power losses, and lower electric bills. if the power factor of the consumer drops below 0.85, they will be charged heavily. When the power factor is low, power and energy losses in power lines and transformers increase and the utilities include these costs in the electricity bill in the form of power factor penalty.

Methods of Power Factor Improvement

. Capacitor Banks

. Synchronous Condensers

. Phase Advancers

Capacitor Banks

Improving power factor means reducing the phase difference between voltage and current. Since the majority of loads are of inductive nature, they require some amount of reactive power for them to function.

The simplest way to improve power factor is to add PF correction capacitors to the electrical system. A capacitor or bank of capacitors installed parallel to the load provides this reactive power. They act as a source of local reactive power, and thus less reactive power flows through the line.

Capacitor banks reduce the phase difference between the voltage and current.

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