Document a4v8q80pjbmgbayq02ew7VXDa

Here are Five Benefits From Installing Capacitor! 1 Lead power factor It Improved 1 Correnf, carried bp supply circuit* ond lho equipment, le redeced. Or more pow'*pro> duclng current con be Iremmlttod over the listing circuit $ System toIMS are cut 4 Voltage drop in the lepplf circuit* it cut 5 Monthly power bill map be reduced II the utility company hoi a pf clout# Capacitors Pay Off Within First Imlalling (hunt capacitor! in Cleveland department stare'! basement chopped pf penalty levied by local utility. Similar units may be the answer for overworked feeders in your plant By 6 W DOUOHERTY, Application Engineer, Genetol Electric Co Capacitors con pay big dividends end fast, at was the oaaa at Hallo Brothers Shaker Square store. The capacitor bank was installed In June 1950 with power factor hanging at about 72%. A penalty clause of the local electric utility company, leveled against a de mand of 147 kw per month, ran up a monthly penalty. Aim in installing the new oapacitor bank was to raise pf to at least 95%. And by so doing the total {n-pockel saving of penally plus bonus amounted to about $645 yearly. locotlen. Capacitors are connected in the power-distribution system adjacent to the central-distribution panel. They are set about 8 in. off the floor and fed through a 200-amp, fused, 3-pale safety switch lapped between the 600-smp main breaker end distribution breakers. Thus the main bresker kills power to all electrical equipment. The safely switch allows operation with or without cspacitort. Thought was given to installing in* dividual capacitors at motor loads, but that plan didn't fit this setup. First off, cable runs between distribution ond load were short'. On top of that, cables in these runs were big enough to rule out benefits that might ba reaped by reducing aoraewbet the ampere toad through such feeders. Capacitor Site. How did we arrive at the size capacitor needed for the desired pf improvement? As in si! pf improve* ineot, basic approach is through tho right-triangle relationship of true power (kw), reactive power (kvar), volt* amperes (kva). i'f being cosine of the angle formed between volt*omperes ond true power. To determine me, knowledge of ex- isting ond desired pf is necessary. Here are the data collected and applied, in our case. First off, metering Is done on the main transformer's primary side. To gel a representative picture of the (tower load a set of readings was tallied for three typical months. Then average nf these three readings was used for calculations. Here are the readings we come up with: 147 kwd, 71 :6% pf, 29,600 kwhr, 28,500 kvor-hr. These figures tepresettled readings taken over a period of 4.33 weeks, or 728 hr. Our desired pf was 95%. representing a pf angle of about 18 deg. Translating the desired pf condition Into kvar-hr, we get kwhr X tangent of 18 deg. coming to 29.600 X 0.329, or 9720. This meant 28,5009720, or 18,780 kvar.hr that had to be removed by capacitors. From here on, it was simply a matter n( considering the reactive power taken by the transformers ond figuring tho overage demand hours' use. The latter was determined by dividing the monthly kwhr by the kwd, or 29,600 -4- 147 201. Then on experience factor is Intro duced. This factor of 1.25, multiplied ly the overage use-hours demand, gives a more accurate picture. So 201 X 1-25 -- 252 hr. Total kvar-hr luod figured nut to lie 8940. Taking this figure, dividing by `T < { / * ^ \ If INOIHEIKIMO AND MANAGEMENT SECTION POWER Year Zooming Pf From 72 to 95 252 hr, and adding in the transformer reactive Joss yielded a figure of 52 kvar of capacitors needed. A 60-kvar unit was selected since that is the nearest stand ard site. /Following through on above, note that the advantage offered by a particu lar number of capacitors appears as the difference between total energy-cost reduclinn and installed cost of new equipment.- By determining this difference throughout a range of installed capaciloiive kvar, we arrive at the moil ef fective installation. Switching Capacitors. [,<t us leave this installation and discuss capacitor applications in general. In some letups automatic or manual twitching may be needed to meet supply or load condi tions that change continually. An unswitchcd shunt capacitor can increase elicuit voltage permanently, but its ef fect on regulation is negligible. A switched capacitor, however, con be arronged both to increase voltage and decrease regulation. The usual unit used to initiate switching of capacitor honks is voltage, but any other quantity (hat can be measured in the circuit Is a likely candidate for (his control job. Type of control selected depends on the prime objective in an installation. A capacitor bank Is conveniently switched in steps. This calls for a mint* mum of eslro equipment. Site of steps generally depends on the moximum change-in-voltage permitted at critical points on the system. Contactors or breakers in a switched bank must be elected with proper regard for the momentary currents and the interrupt* ing duty-imposed by a large concentra tion of capacitance. Equipment suitable for this type of duty is available, and no difficulties result if it is-properly selected and applied. Objectives of automatic switching may sometimes be more easily attained by manual switching of capacitors di rectly with the toad, or by switching that is interlocked with the toad. A limitation on switching capacitors di rectly with induction-motor loads has developed, making it necessary to limit capacitor site applied with a motor lo less than 25% of motor kva. If this limit is not respected the motor-capacitor combination, when dis connected from the supply circuit with the motor still rotating, may build up overvoltage by self-excilatinn in the local circuit formed in the motor reactance and connected oapaciionce. The setting of motor overcurrcnt devices should be rechecked after capacitors are connected directly nt the motor terminals to correct for any reduction in the line current. A workable combination for many plants is to install (1) a permissible and reasonable amount of capacitance along with individual loads, and (2) the required remainder as a portly witched capacitor bank at some con venient location on the distribution sys tem. This plan results in Installing maximum corrective kvar, with mini mum auxiliary switching equipment. Mora and more industrial plants are thinking in terras of secondary unitsubstations as the most feasible spot for the location of the bulk of their capacitors. At this point capacitors bene fit the primary distribution feeders by lowering their ampere load. Units may he automatically twitched as a function' of plant voltage. Capacitors may be installed right on nr near bus duet running throughout the plant. They may be tapped direct into bus duct through a sat of fuses ond disconnect switch. ThU technique fits well with the rapid growth of bus duct for secondary distribution in industrial plonts. When so used, total eapacitor kvar needed for a plant is split Into several units. Then each unit is in stalled in a specific location where it does most good from both pf and redticed-amp angle. JULY 1933 ENOINIfSING AMO MANAGEMENT SECTION il