Power factor correction (Electrical Engineering) 3

Question

In practice, power factor correction is accomplished by adding a capacitor that will return the power factor to about 0.95. Why is it not corrected to 1.0?

Please supply an elaborate answer. Thank you very much.

Answer 1

Power factor is the ratio of true power or watts to apparent power or volt amps. They are identical only when current and voltage are in phase than the power factor is 1.0. The power in an ac circuit is very seldom equal to the direct product of the volts and amperes. In order to find the power of a single phase ac circuit the product of volts and amperes must be multiplied by the power factor. Ampmeters and voltmeters indicate the effective value of amps and volts. True power or watts can be measured with a wattmeter. If the true power is 1870 watts and the volt amp reading is 2200. Than the power factor is 0.85 or 85 percent. True power divided by apparent power. The power factor is expressed in decimal or percentage. Thus power factors of 0.8 are the same as 80 percent. Low power factor is usually associated with motors and transformers. An incandescent bulb would have a power factor of close to 1.0. A one hp motor about 0.80. With low power factor loads, the current flowing through electrical system components is higher than necessary to do the required work. This results in excess heating, which can damage or shorten the life of equipment, A low power factor can also cause low-voltage conditions, resulting in dimming of lights and sluggish motor operation.

Low power factor is usually not that much of a problem in residential homes. It does however become a problem in industry where multiple large motors are used. Power Factor Correction Capacitors are normally used to try to correct this problem.

Answer 2

hi mark is for u to chang the capacitor to a high wait than the one u used be for and see it,

Answer 3

In industrial plants, the advice is to limit power factor to 0.95 only.This is because when capacitors are connected to motor terminals for power factor correction, the terminal voltage rises higher than the normal line voltage during a brief start-stop or jogging operation. The motor windings get overheated and in some instances may result to burning of windings.

Answer 4

if p.f. = 1.0 and Xl=Xc, this may result in resonance which can be undesireable.

Answer 5

There is nothing "magical" about 0.95.  As you approach unity power factor (PF), you reach the point of diminishing returns.  Capacitors come in specific sizes and the one more of the size you're purchasing might "over-shoot" 1.00 and cause a leading PF.

Customers who are billed in kVA often install auto-switching capacitors to get far better than 0.95 lagging.  

Answer 6

It is the most economically feasible value.

Normally in power systems the power factor is inductive So capacitor are used to make it better (close to one)

The amount of capacitors required to  increase the pf by a same amount, increases as it closes to one

ex: if 0.85 to 0.9 requires x no. of capacitors

     0.9 to 0.95 requires more than x no. of capacitors