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- 1. Power Factor basics By: Jafar Khan
- 2. Content What is power factor What causes low power factor Why should I improve my power factor How should I correct (Improve) my power factor
- 3. What is Power Factor? Power factor is the measure of how effectively your electrical equipment converts electric power (supplied by your power utility) into useful power output. In technical terms, it is the ratio of Active Power (kW)) to the Apparent Power (kVA) of an electrical installation.
- 4. • KW is Working Power (also called Actual Power or Active Power or Real Power). It is the power that actually powers the equipment and performs useful work. • KVAR is Reactive Power. It is the power that magnetic equipment (transformer, motor and relay) needs to produce the magnetizing flux. • KVA is Apparent Power. It is the “vectorial summation” of KVAR and KW.
- 5. Simple analogy in order to better understand these terms…. P.F. = KW KVA P.F. = KW KW+KVAR P.F. = Beer Beer+Foam The more foam you have (the higher the percentage of KVAR), the lower your ratio of KW (beer) to KVA (beer plus foam). Thus, the lower your power factor. The less foam you have (the lower the percentage of KVAR), the higher your ratio of KW (beer) to KVA (beer plus foam). In fact, as your foam (or KVAR) approaches zero, your power factor approaches 1.0.
- 6. Let’s look at another analogy …… Mac here is dragging a heavy load. Mac’s Working Power (or Actual Power) in the forward direction, where he most wants his load to travel, is KW. Unfortunately, Mac can’t drag his load on a perfect horizontal (he would get a tremendous backache), so his shoulder height adds a little Reactive Power, or KVAR. The Apparent Power Mac is dragging, KVA, is this “vectorial summation” of KVAR and KW.
- 7. KVAR (Reactive Power) Power Traingle …… Power Traingle… KV A (Ap par e nt P ow er) Ø KW (Real Power) = COS Ø Power Factor (COS Ø) should be close to unity
- 8. What causes Low Power Factor? Low power factor results when KW is small in relation to KVA. Remembering our beer mug analogy, this would occur when KVAR (foam, or Mac’s shoulder height) is large. What causes a large KVAR in a system? The answer is…inductive loads. Transformers Induction motors Induction generators (wind mill generators) High intensity discharge (HID) lighting
- 9. KVAR KVAR KVAR Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in distribution system. This increase in reactive and apparent power results in a larger angle measured between KW and KVA. As θ increases, cosine θ (or power factor) decreases. KV A KV A KV A Ø Ø KW KW
- 10. Why should I Improve my Power Factor? • Lower the Utility bill inductive loads require reactive power, caused your low power factor. This increase in required reactive power (KVAR) causes an increase in required apparent power (KVA), which is what the utility is supplying. So, a facility’s low power factor causes the utility to have to increase its generation and transmission capacity in order to handle this extra demand. By raising your power factor, you use less KVAR. This results in less KW, which equates to savings from the utility. • Increased system capacity and reduced system losses By adding capacitors (KVAR generators) to the system, the power factor is improved and the KW capacity of the system is increased. Reduces I2R losses in conductors
- 11. • Increased voltage level and cooler, more efficient motors As uncorrected power factor causes power losses in distribution system. As power losses increase, you may experience voltage drops. Excessive voltage drops can cause overheating and premature failure of motors and other inductive equipment. So, by raising power factor, minimizes these voltage drops along feeder cables and avoid related problems. Your motors will run cooler and be more efficient, with a slight increase in capacity and starting torque. A 10% drop in terminal voltage from the rated, Will reduce the Induction motor torque by approx 19%, Increase full load current by approx 11%, Reduce overload capacity Increase temperature rise by approx 6-7 degrees.
- 12. Five lightson Fourlight on Three lights Twolightson on Onelights on Six lights on No 25 24 23 Watts total 20Watts total 14 0 (room gets brighter) (some light darker) (room is dark)room) in Voltage drops more Voltage is normal some
- 13. 12/11/97 13
- 14. • Reduces loading on transformers For example, a 1,000 KVA transformer with an 80% power factor provides 800 KW (600 KVAR) of power to the main bus. 1000 KVA = (800 KW)2 + ( ? KVAR)2 KVAR = 600 By increasing the power factor to 90%, more KW can be supplied for the same amount of KVA. 1000 KVA = (900 KW)2 + ( ? KVAR)2 KVAR = 436 The KW capacity of the system increases to 900 KW and the utility supplies only 436 KVAR.
- 15. How do I correct my Power Factor? We have seen that consumers of Reactive power (Inductive loads) decrease power factor Similarly, Sources of Reactive Power increase power factor: Capacitors Synchronous generators (utility and emergency) Synchronous motors One way to increase power factor is to add capacitors to the system.
- 16. • Installing capacitors (KVAR Generators) Installing capacitors decreases the magnitude of reactive power (KVAR), thus increasing your power factor. Reactive power (KVARS), caused by inductive loads, always acts at a 90-degree angle to working power (KW). Capacitance (KVAR) Working power (KW) Reactance (KVAR) Capacitors store KVARS and release energy opposing the reactive energy caused by the inductor.
- 17. If the motor is unloaded and is located a short distance from the generator, the energy from the generator causes magnetic fields to form around the motor coils. Reactive power In both directions between the generator and the motor Feeder line True power delivered to load Generator Output—apparent power (Combination of true and reactive power)
- 18. Since the coils of the motor are reactive, the current causes a magnetic field to expand around the coils during one portion of the alternation. During another portion of the alternation, the magnetic field collapses, induces a voltage at the coil, and causes current from the motor to flow back to generator.
- 19. The current causes a magnetic field to expand around the coils during one portion of the alternation. Reactive power from the generator to the motor For Ascending Positive Alternation
- 20. During another portion of the alternation, the magnetic field collapses, induces a voltage at the coil, and causes current from the motor to flow back to generator. Reactive power from the motor to the generator For Descending Positive Alternation
- 21. The current causes a magnetic field to expand around the coils during one portion of the alternation. Reactive power from the generator to the motor For Ascending Negative Alternation
- 22. During another portion of the alternation, the magnetic field collapses, induces a voltage at the coil, and causes current from the motor to flow back to generator. Reactive power from the motor to the generator For Descending Negative Alternation
- 23. Individual Correction
- 24. Group Correction
- 25. Capacitor sizing KVAr required = kW (tan Ø 1 – tan Ø 2) Where Ø 1 = Cos-1 (PF 1) and Ø 1 = Cos-1 (PF 2) and PF1 and PF2 are initial and final Power factors respectively Q= S2 - P2
- 26. Conclusion PF is the ratio of Active Power (kW)) to the Apparent Power (kVA). More the reactive power, less is the power factor Power factor can be improved by locally providing required Reactive power
- 27. Thank You

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