Document 7O068nk4k2kan021YjqZZ6wGE

ELECTRONICS FOR THE POWER ENGINEER By F A ANNETT, Auecteh IdHof 8--Reactors and Transformers USB OF OH FOR FUEL greotly simplifies plont layout. Eight l-ln.-Hg bockpresiure turbines. The boilers are served by lu- '2j boilers rated 300,000 lb per hr serve four 900-pslg 900-F bular air heotars and bora-tube economisers, two sets of font ^ FM-jot wcthing tfiambtr \ ( 3,000-* twitch far \ / / ScnSbtrt -Hr MAIN TURBINt-GINIRATORS will bo arranged lengthwise in Flue-oos cleaning equipment for oil units will be ecntrollied turbine room with boilers in o single row in the boiler room. obout th.stock locoted ot ptont center toword the rhrer uos up of four 60,000-kw units. The first two ore under construction. The units will operate with 900-psig 900-F steam and exhaust at l-in.-ffg back-pressure. Five bleed points will give a final feedwater temperature of 380 F. The 2cosing tandem-compound units will have double-flow low-pressure casings and will turn at 3000 rpm. The alterna tors are designed for 3-phaso 50-cycle 15,000-v 0.075-pf operation. Separately driven external fans will air cool the main generators. Each unit wifi have (win condensers with a total surface oi 50,000 iq ft or* ronged in two panes using 40,000 gpm (imperial). Duplicate 3-stage steamjet air ejectors serve each unit. Feedwater System. The 5-stage feed heating system will hove s drain cooler. low-pressure heater, gland stcao con- , denser and deoerator on the eucuoo aide of the boiler feed pump* ^ throe high-pressure heaters ,n ^ charge side. This completely d**" circuit will have water flow conlr0 by o closed feedwater valve, sdus , by water level In the condensate ceiver below the main eondener*(Continued on page lw 121 1790) POWER Decern*/ p Ws CoHtwue our study of inductance by considering some of the devices whose design and operation involve either self-inductoncs or mutual Inductmce. One of these is an Inductive resetor, used in several forms In elec tronic and control circuits- leductlve Rooctor. An Inductive reictor may have one coil. Fig. 1, or two, Fig. 2. When it has two coils they ere wound so they magnetize the core in the some direction. In that way tech coil assists -in mognetizing the core. If the. coils were connected in opposition as In Fig. 3, one would neutrslite the magnetising effect o! the other and prevent them acting as an inductive reactance in the circuitSometimes resistance coils are con nected that way to obtain a resistor In which the effects of inductance are negligible. Such a device is a nonindaethre resistor. An inductive reactor In an so circuit bsi the same effect as a resistor. For example, in Fig. 4, assume that when 2 imp flow in the circuit 35 v are induced in the reactor coil, which wo will assume has negligible'resistance. If 115 v is applied across the circuit only 115 -- 35 = 80 v i| effective across the 40-ohm resistor. Vs get the same results in Fig. S, here the reactor is replaced by a 17.5ehms resistor. Total circuit resistance ** <0 + 17.5 ss 57.5 ohms. Current in amperes equals volts divided by ohms, r 115 57.5 = 2 amp. A current of 2 amp through 17.5-ohms resistance | causes a voltage drop oi 2 X 17.S = 35 *, the same u with the reactor. Fig. 4. But the resetor has the advantage of being constructed so it is easily ad* . fat'd by simple means like a saturnt- "ai coil in what is ealled a saturable re*cior. Also, the power losses are fek smaller in a reactor thon In an bivalent resistant*. fetwublo Rsocfer. A saturable re*Qor is a special inductive one through Jj*e sc coil the current it controlled 0 small dc current in a saturating coil. Sinoe on inductance stores energy in Its magnetic field, when current is increasing, end returns it to the power source when current decreases, its energy lessee ere low. Thus, with a saturable-core reactor many kilowatts of power load through its oe coils can bo efficiently controlled by a few hundred welts of power in its dc coil. When we start to msgnetlxe a closed iron core the magnetic flux increases rapidly--in fact, almost directly in pro portion lo the current in the coil. Be yond a certain magnetising current value, increase in flux becomes less and (css for a given current increase. Event- Simple and Saturable Reactors Siegle-coll reactor Is O Double-coil reoctor It Q RDoctor colls grouped ore fitted with 2-l#o core V for opposed polarities 60V -| 4 5An inductive reactor In on ac circuit has the some effect os o resistor Reoctor, Fig. 4, is replaced by I7.Sohm resistor for same voltoge drop *e --7b e*e power supply N frftd-c: tupppffyr\ --1 O ot 02 03 04 O S O 6 07 0 Amperes 0 Magnetic-saturatiIon currvvie'"for Iran ' core like that In saturable reoctor <s. __~.>5 i?-: * 'Soturetlng mi Saturable reoctor has two ec coils ond o dc coil on o 3-legged iron cord *OWEg Qactmber 1948 (791) 129