What is Power Factor Beer Analogy & Misconception Behind

Definition of Power Factor:

The power factor is defined as the amount of wattful power in a system to that of total apparent power flowing in the system. It can also be defined as the phase angle between voltage and current phasors.

 Power Factor =  kW/ kVA = Cos(Theta) 

Active Power, Reactive Power & Power Factor :

We know that total electrical power is the vector summation of active power and reactive power. Active power is the one which is called wattful power as some work is done due to this in the system or some energy is dissipated as heat (resistance). When active power flows in a system both voltage and current phasors will be in phase to each other. Reactive power is the one due to which magnetic field gets generated but doesn't do any wattful work. The current phasor will be in lead or lag with voltage phasor. 

If the system is having purely resistive loads like resistive heating then the reactive power is absent in the system and the power factor will be unity. But for the systems like motors, UPS, drives, etc., there will be a reactive power flow in the system along with active power, and hence the power factor will be less than unity. The value of the power factor can be from 0 to 1 both leading and lagging.

If only inductive loads are there in the system then the system will have a lagging power factor and if it is having only capacitive loads then the power factor will be in leading. If you take an example of a motor due to winding there will be an inductive load and due to connecting power cables, there will be a little capacitive power too in the system. Finally its the combined effect of both inductive and capacitive loads and the system will behave accordingly.

Power Factor Beer Analogy :

Beer analogy is very famous and in fact an interesting way of explaining the concept of power factor. This analogy says that the beer is active power and foam as reactive power. When foam becomes more in a mug whose volume is constant the quantity of drinkable beer becomes low. Up to this, it's perfectly fine but I came across some misconception among some people who explain the analogy stating reactive power is an unwanted component in a system similar to that of foam in a beer mug. This is an absolutely wrong understanding of the analogy. If you take an induction motor it requires both active and reactive power to run. Without reactive power, no magnetic field will be generated in the motor and it can't be started. Actually, active power cannot be generated onsite but reactive power can be generated with the help of capacitors. So with the help of capacitor banks, the reactive power can be supplied locally which can easily avoid the distribution losses in the system. Hence reactive power cannot be treated as an unwanted component instead it's a useful component that can be compensated locally.

Effects of Poor Power Factor :

There are many negative effects in an electrical system due to poor power factor. Poor power factor includes low power factor and even leading power factor due to overcompensation. Below are some of the effects of low power factor:

• Line currents get increased causing more I square R losses.
• System capacity will get reduced ( KVA/ MVA Capacity reduction), This will lead to an increase in capital cost to accommodate new equipment for catering the full load. 
• Attracts penalty from power distribution companies. This is not an effect caused due to technical reasons but the effect caused due to compliance which again, in turn, an effect caused due to the increase in line currents.
• Poor system voltage due to low power factor affects many loads that are sensitive to voltage like lighting, induction machines, etc. This, in turn, causes losses in individual equipment.