Power factor improvement

Editor's Notes

• #3 During recent years, increasing attention has been paid to minimize the energy cost and inefficiency in electricity generation, transmission and distribution In recent years, energy auditing and the power quality of the AC system has become a great concern due to the rapidly increased energy demand and numbers of electronic equipment, power electronics and high voltage power system, In order to reduce the energy consumption and harmonic contamination in power lines and improve transmission efficiency, power factor correction research became a hot topic
• #4 Power factor improvement may be defined as the ratio of the real power to the apparent power. It is a dimensionless quantity whose value lies between 0 and 1.
• #5 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. Let’s look at a simple analogy in order to better understand these terms…. Let’s say you are at the hotel and it is a really hot day. You order up a mug of your favorite beer. The thirst-quenching portion of your beer is represented by KW (Figure 1). Unfortunately, life isn’t perfect. Along with your ale comes a little bit of foam. (And let’s face it…that foam just doesn’t quench your thirst.) This foam is represented by KVAR. The total contents of your mug, KVA, is this summation of KW (the beer) and KVAR (the foam). So, now that we understand some basic terms, we are ready to learn about power factor: Power Factor (P.F.) is the ratio of Working Power to Apparent Power. Looking at our beer mug analogy above, power factor would be the ratio of beer (KW) to beer plus foam (KVA). Thus, for a given KVA: • 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 (Figure 2). 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. The “Power Triangle” (Figure 3) illustrates this relationship between KW, KVA, KVAR, and Power Factor: In order to have an “efficient” system (whether it is the beer mug or Mac dragging a heavy load), we want power factor to be as close to 1.0 as possible. Sometimes, however, our electrical distribution has a power factor much less than 1.0. Next, we’ll see what causes this.
• #7 These inductive loads constitute a major portion of the power consumed in industrial complexes. What is inductive load?
• #8 Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in your distribution system (Figure 4). This increase in reactive and apparent power results in a larger angle θ (measured between KW and KVA). Recall that, as θ increases, cosine θ (or power fac tor) decreases So, inductive loads (with large KVAR) result in low power factor.
• #10 In a c circuit there is generally a phase difference @ between voltage and currnent. the tern cosfive is called pf of the circuit.\ If the circuit is inductives,the current lags behind the voltages and pf is referred lagging. In capacitance circuit,current lead the voltages and pf is to be leading. Its aususlly a practise to attach the word lagging and leading with the numerical value of pf .if circiut has pf 0.8 means there is a 0.8lagging . Some times its expressed in percentages.
• #11 DISADVANTAGES OF LOW POWER FACTOR Its clear from the above that for fixed power and voltage, the load is inversly proportional to the power factor.lower the power factor,higher is the load and vice –versa.a pf less than unity results in following disadvantages
• #12 The electrical machinery(altenator,tranformer,switch gear) is always rated in kva. Kva =kw/ cos ∅ It is clear that kva rating of the equipment is inversly proprtional to pf. The smaller the pf.the larger is the kva rating.there for at low pf, the kva rating of the equipment has to be made more.making the equipment larger and expensive. ***the ele m/c is rated kva the pf of not known when its manufactured in the company. To transmmit or distribute fixed amount of power at constant voltage,the conductor will carry more current at low power factor.this neccesited large coductor size. **** large curent at low pf causes more losses. ****the larger curent at lagging pf cause a greater voltage drop in trasformer,alternator,transmission line and disrtibuton.thus imparing on perforemance of equipements.additional voltage regulator is required. ****bcoz reactive component of current prevents the full utilization of capacity of system.
• #13 You want to improve your power factor for several different reasons. Some of the benefits of improving your power factor include: By raising your power factor, you use less KVAR. This results in less KW, which equates to a rupees savings from the utility. Utilities usually charge customers an additional fee when their power factor is lessThus, you can avoid this additional fee by increasing your power factor.less than 0.95. By adding capacitors (KVAR generators) to the system, the power factor is improved and the KW capacity of the system is increased. Letter see the case study. Uncorrected power factor causes power system losses in your distribution system. By improving your power factor, these losses can be reduced. With the current rise in the cost of energy,increased facility efficiency is very desirable. And with lower system losses, you are also able to add additional load to your system. As mentioned above, uncorrected power factor causes power system losses in your distribution system. As power losses increase, you may experience voltage drops. Excessive voltage drops can cause overheating and15z premature failure of motors and other inductive equipment. So, by raising your power factor, you will minimize 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.
• #14 Thus, it comes as no surprise that one way to increase power factor is to add capacitors to the system. This--and other ways of increasing power factor--are listed here.