# Both stator and rotor have poly phase windings so dc

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Both stator and rotor have poly-phase windingsSoDC motor/machines:The stator winding is connected to dc supply and rotor winding flows ac current.Stator is made of salient pole and Commutator is connected to the rotor so rotorwinding is supply ac power.Induction machines:In induction motor the ac supply is connected to stator winding and rotor andstator are made of poly-phase windings.Synchronous machines:In this type machines the stator is connected to ac supply but rotor winding isexcited by dc supply. The rotor is made of both salient pole and slip rings andstator is made of cylindrical.Q. 46When stator and rotor windings of a 2-pole rotating electrical machine areexcited, each would produce a sinusoidal mmf distribution in the airgap withpeal valuesFsandFrrespectively. The rotor mmf lags stator mmf by a spaceangledat any instant as shown in figure. Thus, half of stator and rotor surfaceswill form one pole with the other half forming the second pole. Further, thedirection of torque acting on the rotor can be clockwise or counter-clockwise.The following table gives four set of statement as regards poles and torque. Selectthe correct set corresponding to the mmf axes as shown in figure.Downloaded From : Downloaded From :
GATE SOLVED PAPER - EE2003StatorSurfaceABC formsStatorSurfaceCDA formsRotorSurfaceabc formsRotorsurfacecda formsTorqueis(A) North Pole(B) South Pole(C) North Pole(D) South PoleSouth PoleNorth PoleSouth PoleNorth PoleNorth PoleNorth PoleSouth PoleSouth PoleSouth PoleSouth PoleNorth PoleNorth PoleClockwiseCounterClockwiseCounterClockwiseClockwiseSol. 46Given thatFsis the peak value of stator mmf axis.Fris the peak value ofrotor mmf axis. The rotor mmf lags stator mmf by space angled. The direction of torque acting on the rotor is clockwise or counter clockwise.When the opposite pole is produced in same half portion of stator and rotorthen the rotor moves. So portion of stator is north-pole in ABC and rotor abc isproduced south pole as well as portion surface CDA is produced south pole andthe rotor cda is produced North pole.The torque direction of the rotor is clock wise and torque at surface is in counterclockwise direction.Hence (C) is correct option.Q. 47A 4-pole, 3-phase, double-layer winding is housed in a 36-slot stator for an acmachine with 60cphase spread. Coil span is 7 short pitches. Number of slots inwhich top and bottom layers belong to different phases is
Sol. 47Given that:A 4-pole, 3-f, double layer winding has 36 slots stator with 60cphase spread, coilspan is 7 short pitchedso,Pole pitchpoleslot=4369==Slot/pole/phase3=so,3-slots in one phase, if it is chorded by 2 slots thenOut of 32"have different phaseOut of 3624"have different phase.

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Term
Summer
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Tags
Electric motor, Sol