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When Stator and Rotor windings of a 2-pole rotating electrical machine are excited, each would produce a sinusoidal mmf distribution in the air gap with peak values Fs and Fr respectively. The rotor mmf lags stator mmf by a space angle δ at any instant as shown in Fig. Thus, half of stator and rotor surfaces will form one pole with the other half forming the second pole. Further, the direction of torque acting on the rotor can be clockwise or counter-clockwise.
The following Table gives four sets of statements as regards poles and torque. Select the correct set corresponding to the mmf axes as shown in Fig.
[2 marks]Stator
Surface ABC
formsStator
Surface CDA
formsRotor
Surface
abc formsRotor
Surface cda
formsTorque is A North Pole South Pole North Pole South Pole Clockwise B South Pole North Pole North Pole South Pole Counter
clockwiseC North Pole South Pole South Pole North Pole Counter
clockwiseD South Pole North Pole South Pole North Pole Clockwise
asked in Electrical Engineering, 2003
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628.
Following are some of the properties of rotating electrical machines
P. Stator winding current is dc, rotor-winding current is ac
Q. Stator winding current is ac, rotor-winding current is dc
R. Stator winding current is ac, rotor-winding current is ac
S. Stator has salient poles and rotor has commutator
T. Rotor has salient poles and sliprings and stator is cylindrical
U. Both stator and rotor have poly-phase windings
DC machines. Synchronous machines and Induction machines exhibit some of the above properties as given in the following table. Indicate the correct combination from this table
[2 marks]DC machines Synchronous machines Induction machines A P.S Q.T R.U B Q.U P.T R.S C P.S R.U Q.T D R.S Q.U P.T
asked in Electrical Engineering, 2003
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629.
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630.
