when power factor drop , we add a capaciter across Ac moter. how does it work ?

Question

when my PF drop i add one capaciter across AC moter to incerese my PF . I just want to Know whow this capaciter work. Is their any equation to know that this much of Pf drop requir this much of capaciter.

Answer 1

When and AC motor runs it consumes both Active Power and Reactive Power.

The Active Power = kW= 1.732 x kVxIx cos phi
The Reactive Power = kVar=1.732 x kV x I x sin phi

Together they consitute what is called Apparent Power = kVA

(kW)^2 + (kVar)^2 = (kVA)^2

The power factor = cos phi(typically 0.8)

When the power factor is lagging the load is said to be reactive and consuming Reactive Power from the system for which the Power factor lags.

When the Power factor is leading the load is said to be capacitive and delivering Reactive Power to the system.

So as you can see when the lagging power factor drops(say 0.6-0.7),actually the motor is highly inductive and consuming more reactive Power.

A capacitor bank(Reactive power source) at the load terminal supplies the need of Reactive Power to the motor(inductive load) thus decreasing the consumption from the system(Power source).Thus the system power factor improves.

Typically the System Power factor is kept at 0.8 lagging and the capacitor is selected based on the present power factor and desired power factor(thus calculating the difference of Reactive Power requirement from the capacitor).

Answer 2

I can address only part of your question.

When the power factor is 1, the current and voltage are in phase. The go up and down exactly together. When the power factor is less than one, either the voltage leads the current, or the current leads the voltage.

These two conditions occur because of loads that are capacitive or inductive. If the load is capacitive, an inductor can bring the current and voltage back into phase. If the load is inductive, a capacitor can bring them into phase.These phenomena occur only with AC, and with loads that are not pure resistive.

Answer 3

There are 2 types of powers in ac electric circuits
(1) Active power= V*I*Cos phi kVA
(2)Reactive power= V*I*sin phi kVAR
Therefore, total power(apparent power)=(1)+(2)

The active power actually feeds the load requirements.
Reactive power consumes more current from the line and thus causing power loss

With inductive loads,reactive power is high.It is not desirable.
For that cases,we have to control reactive power by supplying another source of reactive power.
Capacitor is a reactive component.It supplies the needed reactive power and thus the powerfactor goes leading from lagging.Hence the losses are minimised

Answer 4

capacitor is an instument which stores energy and can be used when there is drop of PD.