Document 0qm2x4nLere9QY9rGwvVZ4qvk

when to generate w Industrial power generation has risen slightly ft*.' cent years but nowhere as last as has amQu ' J, energy purchased. This relative decline m irtduswfil! --&VCj.Iewtat'ePvrde*aCrt.oionintao--llast.ehihnnoouutPhlidareomvbd8eb--s the ulilily company, wconnwsiduemrewd in many economical In indus- generation stems lrom the (act that, In general ~ ^witor* large quantifies of process heal are re small private plant is less fitted to cope with jf''particularly where Ihe relationship of heal costs oi luel and labor than is the large central ttaw^ i ioat*a is auc^,tv^aIi or most *^e e^oc,ri' tYot in spile ol (his general trend, decision to aSb ? or buy depends on the ollen complex eoonomlc*S| ^ each individual situation. VuC* /'Sp^ergy can be generated as a byproduct ol ^^J^heal demand. AvoilabiJily ol cheap byprod- w^wCMte fuels also favor* generation. withhiah Purchasing energy avoids need to make a ralal^ > .-'.it* without procmeasys ^de^m^a' nod' sxorimby...p.a.r..o...dt..ue.. .c..t ftuhueo:,,lssKe. large investment in generating equipment. Many ^HT i tors wheve conditions apy duMriolUls today boliov# that capital invested l&fc, rmil etlirionl ufiUty opro''"be ab(e to bay manulacturing lacitiliBs yieldso prsoterreturn.rare cases, you may bre)iabmty, Btc. also believe lhal purchasing- ene--r9g*y give, mmoorres nomic flexibility to meel business slumps, or changejfvy need, in and don't over- in markets and products. And they feel it shifts pro\>i^ - lems ol operating and maintaining generating equlp'V* ` all cases. ru_. possibility ol buying part and making part. Is outdoor generation practical? Rising building costs make outdoor generating lacllities look more attractive. Yet among contra! sta tion designers wha have had wide experience wilh outdoor construction (hero's still lots than lull agree ment at to how iar ii pays lo go. Against savings In building structures you must slock cost of protecting outdoor equipment and. some soy, higher cost* of operation and mainte nance influenced by weather conditions. Certainly. If your new plant will enjoy a favorable climate, look Into the many possible outdoor and seml-outdoor layouts. Check carefully into effects on operation and maintenance. And H you decide to go outdoors, be sure to "sell" yaur operating force on the practicality and merits of it. If you decide to generate all your needs, or part, study faclor*0 `3affecting size and number of units, look into short-cirtuit ratio IIII y*Aou.. decide _t_o__g__e_n__e_r_a_t_e. you need to look into some basic considerations ol generator selection--size and number ol units, and their characteristics. Generating Unit*. We use the term "generating unlit" advisedly, since per formance ol the prime mover is perhaps Avon more important than that ol the generator and w must always think in terms ol the combination. Here are somo considerations that ofleci decision on number and site ot units; In general, cast per kv o( generating unlls goes down as site goes up. Ef ficiency usually improves as size goes up. (This'ie notably the case with steam plants; efficiency of diesel and hydro unite doesn't change as markedly wilh site.) Operating labor costs are more nearly proportional to number ol unito installed than to toial plant capacity. In any glvon generating unit, ellideney varies with load, ft's usually fow at light loads, rising to a "beet point" somewhere between 75% and lull lead and lolling off slightly at higher loads. Shape ot the eiHcloney curve depends on type of prime mover, and to a lesser degree on site, design, etc. Nature ei Load. Above characteristics oi generating units point In the direction ol supplying load with one large unit. Yet this is rarely possible because ol load conditions. Take the question of continuity, lor example. Where operation is continuous and Interruptions are costly, reserve capacity is indicated, not only lor (arced outages but lor scheduled maintenance outages, It's usually more economical WJ * See that ihe goneroior is able to with What significance has (hie in an in to provldo reserve lor several -`hidting unit *!** lo plant load conditions. units than lor one large one. A typleqp`V ProWeni ol obtaining a good balanco setup might use three units, any two oil '^between process-steam and electrical which can carry Iho load. This also pro- ' j' 'docndi also influences number of vide* economically lor load growth-'Hjj* -^tnlts. since more than one type of steam stand any overspood it may meet in service. This is generally 85 lo 100% lor walorwhoel generatore. 25% for enginedriven and 20*4 toy (urbine'-driven units. In probing ihe characteristics of Indue, dustrial-generator specification? High ecr gives desirable voltage stability characteristics, but lo got it designer must put more copper and (ran in the generator. This moons largor housing adding a unit gives (our machines vithU-'"'! -/'%'lurbine may be required. any three able to carry lull plant load.'!^ ;''Generator Characteristic*. Now let's look Where continuity is a lector, alwoyi .Vy ] at the generator Itself. Start by checking check to see what standby service, ii >3v| ^^'characteristic* as catalogued in manu- any, your utility can provide, and what -^! rt^hfsefurers' literature. Standard-design it costs. *V;J ^.yjvnerolore meet most ordinary require- Lead lacier also exerts strong Influence. "L- ' i' .eents but a "special" may bo Iho an- Low load (actor works ooainst use cl fntr to highly fluctuating loads, pulsat- one or two large units since much el the . 'V log* driving torques, abnormal power operation would necessarily be on th >ci .'factor*, especially loading or unhai- low pari oi Iho elllciency curve. A owed single-phase loads. Where you special problem In some industries ii , ,, Intend to operate new generators In weekend load, which may require a *j| * parallel with existing units, make sure special small unit. The load-duration TXT fT'-'thol prime-mover, governor and genera- curve proves a valuable device lor re- 'r\ ,-y' : Mr characteristics are compatible. trial generatore It's a good Idea to con sult suggested specifications proposed by NEMA lor ihe lypo oi genoralor unit under consideration. 8hort-Clfcul) Ratio. Mot in every gen erator specification, the term ihorf-c/rcuft ratio (ecr) may no) call immediately to mind Us full meaning. Th* textbook doll, nitfon i* "ratio ol Held current required to produce rated voltage at rated speed and no load lo ihe field current required to circulate rated stator current when oporallng at rated speed under sus tained short-circuit conditions." and structural parte, greater weight, higher cost. Other drawbacks are highor initial and sustained short-circuit cur rents and some increase in generator losses. Bui today desired stability character istics con be obtained at lower ecr values because ol improved excitation systems. These are more sensitive and able to produce iho rapid and large changes in Held current needed to ac commodate new conditions. Trend over the years is to lower values of ecr, smaller and less costly generators. AUo consider layout of cooling equipment, exciter cooling and speed, generator. In the past, generator air coalers were uxuolly in the base ment directly below the machine. Today's units oiler thorn built into the frame or directly alongside it. This is imporlani where noncondenelng units are used since tho basement may be eliminated. Choice dopends on a comparison ol cost el basement construction against increased cast ol generator with cooler built in or alongside. Don't overlook reduced duct work and installation cost and easier maintenance oi the above-floor layoul. Exciter*. Separate cooling syslome for generator oxdlert are now available. One justification lor a separate system is the difference in cooling requirements. Reducing cooling pres sure in the exciter rules out possibillly oi air bubbles work ing their way in and through bearing lubricant. White you look ai Ihe exciter (rom tho cooling angle, con sider its oplimum speed. This applies particularly to enginedriven ganeralore running below 600 rpm. In such cases, con sider belling the exdler eo it operates at a higher speed. Think in term* ol a maximum speed of 1750 rpm to gel maxi mum speed ol response in your voltage-regulating systemRegulation. Standard generator regulation figure of 4(MS% at 0.6 pi will satisfy most requirements. Bui thero are excep tions. Typical would be the case of a paper mill, where the large chipper motor, biggest single load, would influence selection ol generator capacity and eel a precise vollageregulalion requirement. Storting needs of this single heavy load might materially change the 40-45% figure above. Generator Voltage. In general, generator voltage Is o lunctfon of load size, distanco from generator to load, voltage of con nected system and, in a growing number ol eases.' the lz* of Ihe largest single load unit. Standard voltage ratings lor various generator sizes are catalogued by NEMA as tallows. For smalt ac turbine-genera tors in the 7S- to 400-kw range, standard ratings are 240, 480. 600 and 2400 v. For geared-lurbine synchronous generator* 500 to 1500 kw, voltage range is anywhere from 24Q lor 500 kv to 4160 for 1500. Minimum standard voltage for 1000- and lS00-kw units In this class is 490 v. All other geared units can TODAfS ElECYllCAl MACTICC eOWH '. regulation and voltage rating. Remember -- voltage trend keeps moving upward he luppiled at 240, 460. 600, 2400 and 4(60 v. Stick fo these standard volloge ratings; where passible select the highest. In still larger sites, namely dlreet-eonneclod turbine-generator* rated 2000 to 10,000 kw. Inclusive, available voltage rat ings ore shown In the chart, right. In all questions ol generator voltage, keep In mind the bend toward generating at higher voltages tup to 13.8 kv) Qnd distributing at that voltage to secondary substations. Modernisation. In any modernization program, review Ihe voitage quostion completely. Always think in term# ol higher generator and distribution voltages; transformers will serve well to tie sections ot different voltagos. In adopting higher ullages study Ihe insulation techniques used by each gen erator builder. How the makeif copes with winding bracing Snd insulation problems In general may aflect your malnte- ' nance requirements for years to come. If you plan, at somo later date, to swing from dolla fo Y connection to boost generator voltage, make sure Ihe gen erator (s now connected delta, ociosts foil TODAY'S ElECIIICAL PIACTICC