. Electric traction and transmission engineering . A s N A s N A S N A s [8 POLES] [4 poles! 1 2 3 4 5 6 7 8 1 \ Cc ^ Sh v_ ^ / \ ) 1 c Fig 1 > 44 into the two parts 1-2 and 2-3 by a tap 2 at the middlepoint of the winding. Terminals i and 3 connect with thewindings of the two other phases, which for clearness arenot shown in this figure. The winding shown in Fig. 44differs from the usual induction motor winding in that onlyalternate poles are wound. To produce an 8-pole magneticfield the windings 2-1 and 2-3 are placed in parallel with eachother by connecting tap 2 to one of the line wires
. Electric traction and transmission engineering . A s N A s N A S N A s [8 POLES] [4 poles! 1 2 3 4 5 6 7 8 1 \ Cc ^ Sh v_ ^ / \ ) 1 c Fig 1 > 44 into the two parts 1-2 and 2-3 by a tap 2 at the middlepoint of the winding. Terminals i and 3 connect with thewindings of the two other phases, which for clearness arenot shown in this figure. The winding shown in Fig. 44differs from the usual induction motor winding in that onlyalternate poles are wound. To produce an 8-pole magneticfield the windings 2-1 and 2-3 are placed in parallel with eachother by connecting tap 2 to one of the line wires and tapsI and 3 to the neutral point of the phase windings. Thecoils are so arranged that when tliu§ connected they prg- RAILWAY MOTOR CONTROL. 99 duce poles which are all of the same polarity. Interme-diate poles of opposite polarity will therefore be formedbetween them, thus producing an 8-pole field as , however, a 4-pole field is desired, windings 1-2 and2-3 are placed in series by connecting terminals i and 3 to POLES POLES Lj:. o- -GROUND Fig. 45. line wires of the three-phase supply. One of the windingsis thereby reversed with respect to the other and conse-quently the poles pertaining thereto will be of oppositepolarity. The intermediate poles will then disappear, re-sulting in a 4-pole field. Fig. 45 shows the schematic ar-rangement and the controller connections for simultaneouslychanging the number of poles of all three stator phases. lOO TRACTION AND TRANSMISSION. (c) Cascade Method. The third method of three-phaseinduction motor control consists in operating two motorsin cascade. In the cascade connection, or concatenation,of two induction motors, the rotors of both machines aremounted on the same shaft or otherwise mechanicallycoupled as by gears or connecting rods. The primary ofthe first motor is connected to the line and its secondaryis connected to the primary of the second motor. Thesecondary windings of the latter machine are short-cir-cuited t
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