Document 3JVpLdKyay0rVLr1yb7RV6Xp6

2/b components: transformers Today's transformers offer lop reliability and highier efficienty',,v gsliarcl an(t dry types are moving ahead for indoor installationTransformers get a heovy play the industrial plant for primary and secondary substations, chang ing voltage at individual ma chines, matching lighting needs (p 123). They're broadly classed as wet or dry. In wet types the liquid, oil or askarel, serves as a primary heat-transler medium and insulator. Dry types use air or in ert gas in place of liquid. Askarel and dry types are being used increasingly In unit substations. Transformer Design. Trend is to ward greater solely, dependabil ity, sleek appearance, and to higher voltages and ratings lor single units. In large transformers, tap-changing under load Is now well established (pp 82. 63). Im pulse testing as the manufac turer's "proot tost1' o! design has contributed much to growing de pendability. Grain-oriented steels in cores have raised flux densitie^ v during WS",0[ *or^h^"*- Field experience has conformed!/'' *gffih.prov*l steels have boen manufacturers' belief that the lour*- * i^j Vdctor in reducing physical available oil-preservation V'ritsrfor a given rating. Further ods (Power. June 1952, p ?9| .rjSaeering may come with im- maintain oil in serviceable centk'Jfe V^eyed insulations. But pendulum tion. Even so. mineral oil is nov'^ It fray'swing in (he other direction If available with inhibitors aimed tgi;*'' tf^ol aluminum grows; lor given cut oxidation and sludging. Port-vV; k<^en( rating, more aluminum able oil reclaimers "ar"e ubeing uxed -V l^'^&sectiona) area is required. while transformers are energy li-.V.-^oane manufacturers are now lurn- to sandwich in mafntenatno oper-:& out aluminum-wound units. Another factor in size reduction that also cuts cost is the single 3phase unit, now used in place of three single units. Considering top reliability ol today's transformers there's (ittie justification for lean ing on more costly open-delta plan. Insulation. As more is learned about (he (rue limits of each In sulation, the amount is generally reduced. Greater dependence Is placed on arresters to cope with overvo-lt-a--g--e--s----r-a-tahTMer than Insula tion bulk. Sealed tanks and mod ern oil-preservation methods have helped to stretch insulation life. Tomorrow's insulations will grow out ol synthetics rather than organic materials. Typical today is class H (p 114). Vented dry types are now available with class H; this permits operation in humid atmospheres without using space heaters during shutdowns. Od^and askarel-filed units offer highest impulse levels while?: $0r types boast light weight, greater simplicity of installation m*1' ( I: Biggest Wo voiutno ol transformers i ol|-ll)l*d. generally limited >o today's outdoor primary substations. Flroprool vault is needed ll put indoors. Watar-spray or CO* extinguishing systsms. manual or automatic, are used for Important units. Water spray is insulator (POWER. Oct. 19S0. pp II0-H3) and protects adjoining bays. CO. is good lor vaults. free-breathing units are largely superseded by conserva tor type and sealed-nitrogen units to hold absorption oi oxy gen and moisture to a minimum. Hewer design* employ an oil-conditioning unit, built Into transformer lank wall. Astare/, a nonllammable liquid, side-steps oil's lire hatred yet rotalns high impulse level. Uso only In transformers spe cifically designed lor it. Indoors or out. II indoors above IS kv, keep in vaults lor high-voltage prelection. Chlorine gas is generated II arcing occurs in tank. So units over 2$ kva have (I) pressure-relie! vent leading to outdoor Hue. or (2) gas absorber installed on transformer case. Engi neer* lean toward gas absorbor to avoid running Uue. In some plants, especially vrelt-vonUlated ones, local Inspscwt may permit venl alone, minus flue or absorber. l^lhm are getting a big bid In industry today. They eViminat* oainlvnance o( liquid*, yet present new problems of their own. Dirt accumulates within housing so side plates must bo \`- ' rsmoved occasionally and the unit blown oul. !?. Avoid inslallation in production areas ol textile and chcmi- _tal plants,- lint and lumes ore trouble sources. Consider locat ing in well-ventilated, separate room in such plants. With - Mne Insulations you may run Into moisture-absorption prob lem during shutdown in seasonal plants. Power ongineors are ticking this with built-in electric heator*. Here U newest addition to transformer family. Although pre mium priced, U otters absolute sealing with inert gas at slight positive pressure. This keeps air. conlominants and moisture Irom windings. There is no maintenance other thon occasional inspection. And this design Is less noisy than vented dry type -- on Important angle In eorne installations. Befog submersible, there's no need for a special location whan installing. But If serious flooding is a possibility, give thought to addilional anchoring. Future: Power engineers will (ait see its advantages and lustily added cost. Fan cooling or a larger transformer? Here are the factors to check before deciding Power engineer* lean toward newer sealed dry type for wet, dirty or hot locations A forced-air coaled transformer with two eels el fans may have three ratings: (!) self cooled (2) with one set of fans (21 with all tans. This Is a tiiple-iated unit. Hlgh-velocfty fans can boost top rating ol large liquid-tUted transformers to 1.67 times soif-coofid rating. Dry-type units usually benefit greatly from Ians because cooling air comes in direct con tact with windings. Pros an'' Cons. Fans are often specified on industrial transformers since they are one ol the lew means ol increasing rating of an existing installation IPOWM, lune 1952. pp 76. 77). But be cause (ant increase rating by a per centage of the seif-cooled rating, bene fit ts small on small units. Cast ol Ians and conirots is relatively fixed, so many engineers can't see their value tor transformer" below 500, or even 750, kva. But at 150Q-2CQQ kva and up. tans olten prove quite economical. Consider' transformer losses when operating at higher ratings with Ian*. Other factors are noise and maintenance -olten higher for fans and controls than for unit itself. So carefully evaluate whether tans, or next larger transformer. Is best long-run bot. Using Fan*. Farced-alr cooling may be used to: 0) provide additional capacity for peaks, with normal foods handled by natural circulation (2) tower oil and capper temperatures where ambient is high and unit couldn't cany lull rated food without exceeding recommended temperature^ (3) carry larger continu ous load than tho sell-cooled rating would allow. This last scheme ollen leads lo select ing a smaller transformer than Is really needed. Power engineers (town on It a* shortsighted. Bent use of Ians is for peaks or lo provide for future loads In latter case, arrange for cooling when you buy the unit, then you can easily add fans later II capacity Is needed. TOOAT'i ClCCTIrtCAl tucrtcc fOW<* Looking info tho post, we can see the now.rollred air-blast transformer used forttreel-raiiwoy work as the forerunner el today's dry type. Modern designs, node their formal bow )n the early . 1930's. Some 12 years ago, sealed units cams in, and with them inert gases. Vseled Designs, Vented dry types with (fait B insulation have been used for years, usually In clean, dry surround ings. But Ihey'vo fared well even under tough ambients. During World War U many were exposed to moisture, JInt, dust and sometimes corrosive fumes. That they stood up under these nonrecom* mended conditions, even though for relatively short periods. Is q tribute to modern transformer dosign. Hewer seated designs would have been a better choice. When speetlying sealed units, power engineers consider their many advantages: (I) tittle main tenance Is needed. {21 Transformers can be installed in dirty locations provided periodic checks are mods on bushings and gas pressure. (3) Units can be used indoors, outdoors, even where flooding ts a possibility. (4) Contaminants can't got atInsulation todecrease voltage strength. <5) Minimum oxidation means longer insulation Hie. Today's Boated Units. These (alt into one of two groups, based on Insulation used: doss B ot class H, (Both insula tions are also available in vented units.) Right now, etas* H Is highest in cost. Some engineers, bating lhair thinking on held tests, lee) a nitrogen-seated unit with class 6 Insulation wfff operate in class H temperature tone without ma terial effect on (ffe. Bui majority looks to the dass-H-ln- suloted unit, preferably sealed In nitro gen, as (he one to select for holding tomorrow's maintenance cost* In check, ft ts being installed where exfremas in food, temperature and atmoepheric con ditions must be met successfully. oaoftii tew TOOAVS tlECUICAt HaCTICI 9T lib