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Power factor correction

Date post: 14-Jan-2016
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Power factor correction. √. P ower factor is the cosine of angle between V and I. S 2 = P 2+ Q 2. Power factor is the cosine of angle between V and I. From power triangle p f = (VIcos Φ )/VI = Active power/ Apparent power S 2 = P 2+ Q 2 - PowerPoint PPT Presentation
Power factor correction
Page 1: Power factor correction

Power factor correction

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Page 3: Power factor correction

Power factor is the cosine of angle between V and I

• From power triangle• p f = (VIcosΦ)/VI • = Active power/ Apparent


• S2 = P2+Q2

• Apparent power2 =active power 2+ reactive power2

S2 = P2+Q2

Page 4: Power factor correction

• Pf plays an important role in ac ckts since power consumed depends on pf

• P=VLIL cosΦ , IL = P/VL cosΦ , for 1Φ ,

• P= √3 VLIL cosΦ IL = P/ √3 VL cosΦ , for 3Φ

• It is clear that for fixed P and V the load current is inversly proportional to pf

• Therefore for lpf ,higher will be the load current

Page 5: Power factor correction

Disadvantages of lpf

• Large kVA rating of the equipment-kVA=kW/cosΦ .This makes the equipment large

and costly.Greater conductor size-Large Cu lossPoor voltage regulation

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Causes of lpf

• If pf is less than 0.8 it is regarded as lpf.• Most of ac and induction type motors have lpfThey work with very small pf during no load

(0.2-0.3) and rises to 0.8 - 0.9 at full load.Arc lamps ,Electric discharge lamps , heating

furnaces etc operate at lpf.Load variations in the power system causes

increase in magnetising current.

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Pf improvement

• Cause of lpf is the presence of inductive load.• Therefore some devices taking leading pf can

be connected in parallel to improve pf of the load.

• One such device can be a capacitor.It completely or partially cancells out lagging current.

Page 9: Power factor correction

C draws current Ic that leads supply voltage by 90 degree. Resulting current is

the phasor sum of IR and IL-IC, I1is at Φ1 and I2 is at Φ2. Since Φ2 is less than Φ1 , angle of lag has been reduced and the power factor has been improved

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Foll. points may be noted

•The ckt current I2 is less than I1 after pf correction•Active component remains the same before and after pf correction•I1cos Φ1 =I2cos Φ2

•But I2sin Φ2 =I1sin Φ1 - IC

•VI1cos Φ1 =VI2cos Φ2

•Active power remains the same

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•VI2sin Φ2 =VI1sin Φ1 -VIC

•Therefore net kVAR after pf correction =lagging kVAR before pfcorrection – leading kVAR of equipment

Page 13: Power factor correction

Pf improvement devices

• Static capacitors• Synchronous condensors• Phase advancers