how can improve Power factor and method to improve power factor

Power factor and method to improve power factor:

POWER FACTOR:

   

       It's the ratio between the true power (real power) doing useful work and the apparent power of the supply system in a circuit in which both voltage and current are in step,  the power factor is 100%  or UNITY.

    

      For certain technical reasons,  such as the inductive effect of a motor or other apparatus,  the  current may lag behind the voltage.  In such a case,  only a part of the current becomes available for doing useful work,  and is referred a lagging power factor. 

     

      For example,  if only 75 current does useful work the true power is 75%  the apparent power,  and in this instant the power factor is said to be 0.75.  T remaining 25%  of the current in the circuit is termed wattles or idle current.

      Many supply authorities,  therefore penalize the consumer for a bad power factor,  or give a rebate for a satisfactory power factor which allows a better employment of their distribution system 

Disadvantages of Low Power Factor:

power factor equation

If  P &  V_L are constant,  the load current  l_L ,is inversely proportional to power factor.  Lower the power factor,  higher the current and vice versa.  Hence the current for a given load supplied at constant voltage,  will higher at lower power factor and low at high power factor The high current due to poor power factor

    The undesirable effect of operating a low load at a low power factor is due to the large current required for a low power factor. The important disadvantages of low power factor are

• Higher current is required by the equipment,  due to which the economic cost of the equipment is increased.
• At low power factor, the current is high which gives rise to high copper losses in the system and therefore the efficiency of the system is reduced.
• Higher current produced a large voltage drop in the apparatus. This results in the poor voltage regulation.

Since both the capital and running cost are increased, the operation of the system at low power factor (whether it is lagging or leading) is uneconomical from the supplier’s point of view.

                   

Mathods to improve Power Factor:

1) Static capacitors: PF can be improved by connecting the capacitors in parallel with the equipment operating at lagging power factor. Static capacitors have small losses,  requires almost no maintenance and are available in small size. 

2) Capacitors draw current leading the supply voltage by π/2 and neutralize the wattless component of current drawn by the equipment across which these are connected.Capacitors may be connected either in star or in delta. These capacitors remain connected permanently in parallel with the equipment 
  
3) Synchronous motors: Synchronous motor under over excited condition operates at a leading power factor. synchronous motors are therefore employed in large power installations for improving the overall power factor of the installation. 

4) A synchronous motor at no load behaves as a variable condenser or inductor by simply varying its excitation. The machine operated undersuch condition (motor on no-load or light load)  is known as a synchronous condenser and find application in large integrated power systems for improving the power factor under heavy load conditions and for deproving the power factor under light load conditions.