Hoe does capacitor improves power factor?

A capacitor only improves the power factor when the load impedance contains more inductive reactance than capacitive reactance. Capacitive reactance advances current with respect Voltage whereas inductive reactance delays current with respect to Voltage. Adding capacitance to an inductive load impedance advances the net load current forward toward being in phase with the applied load Voltage. Now since the power factor is equal to the cosine of the angle between the load Voltage and the load current it should be obvious that as the angle becomes less as a result of adding capacitance then the cosine of that angle will become greater until it reaches a maximum of 1. Of course 1 is the maximum value the cosine of any angle can have and thus is the maximum power factor any electrical load can have. The power factor equals 1 when the load`s inductive reactance equals the load`s capacitive reactance leaving the net load impedance completely resistive which is ideal for delivering the maximum power for a given amount of source Volt-Amps.

as you know, in capacitor the current has 90 degrees triangle forward than voltage and in inductors' current is 90 degrees backward than voltage, so because all motors are likes inductors because of theirs winding so capacitance reduces the angle between current and voltage and cause higher power factor and less energy consuming and high efficiency.

Power Factor Improvement Using Capacitor

The term power factor comes into picture in AC circuits only. Mathematically it is cosine of the phase difference between source voltage and current. It refers to the fraction of total power (apparent power) which is utilized to do the useful work called active power.



Need for Power Factor Improvement

• Real power is given by P = VIcosφ. To transfer a given amount of power at certain voltage, the electrical current is inversely proportional to cosφ. Hence higher the pf lower will be the current flowing. A small current flow requires less cross sectional area of conductor and thus it saves conductor and money.

• From above relation we saw having poor power factor increases the current flowing in conductor and thus copper loss increases. Further large voltage drop occurs in alternator, electrical transformer and transmission & distribution lines which gives very poor voltage regulation.

• Further the KVA rating of machines is also reduced by having higher power factor as,



Hence, the size and cost of machine also reduced. So, electrical power factor should be maintained close to unity.

Capacitors are used when the power factor is leading and inductors are used when the power factor is lagging. We have a lot of three phase motors where I work at that act as inductors and our power factor is very good. The best power factor is lagging a small amount to keep the electrical utility happy.

good job Rahma....I copied your answer for use at a later time...the E