1
GATE EE 2003
MCQ (Single Correct Answer)
+2
-0.6
A 3-phase Inductor Motor is driving a constant torque load at rated voltage and frequency. If both voltage and frequency are halved, following statements relate to the new condition if stator resistance, leakage reactance and core loss are ignored.
P. The difference between synchronous speed and actual speed remains same
Q. The air-gap flux remains same
R. The stator current remains same
S. The p.u. slip remains same
Among the above, correct statements are
A
All
B
P, Q and R
C
Q, R and S
D
P and S
2
GATE EE 2003
MCQ (Single Correct Answer)
+2
-0.6
A single phase induction motor with only the main winding excited would exhibit the following response at synchronous speed
A
Rotor current is zero
B
Rotor current is non-zero and is at slip frequency
C
Forward and backward rotating fields are equal
D
Forward rotating field is more than the backward rotating field
3
GATE EE 2003
MCQ (Single Correct Answer)
+2
-0.6
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

A
DC
Machines
Synchronous
Machines
Induction
Machines
P.S Q.T R.U
B
DC
Machines
Synchronous
Machines
Induction
Machines
Q.U P.T R.S
C
DC
Machines
Synchronous
Machines
Induction
Machines
P.S R.U Q.T
D
DC
Machines
Synchronous
Machines
Induction
Machines
R.S Q.U P.T
4
GATE EE 2003
MCQ (Single Correct Answer)
+2
-0.6
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 $$\delta\;$$ 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. GATE EE 2003 Electrical Machines - Induction Machines Question 45 English 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 Figure.
A
Stator
Surface
ABC
forms
Stator
Surface
CDA
forms
Rotor
Surface
abc
forms
Rotor
Surface
cda
forms
Torque
North
Pole
South
Pole
North
Pole
South
Pole
Clock
wise
B
Stator
Surface
ABC
forms
Stator
Surface
CDA
forms
Rotor
Surface
abc
forms
Rotor
Surface
cda
forms
Torque
South
Pole
North
Pole
North
Pole
South
Pole

Counter
Clock
wise
C
Stator
Surface
ABC
forms
Stator
Surface
CDA
forms
Rotor
Surface
abc
forms
Rotor
Surface
cda
forms
Torque
North
Pole
South
Pole
South
Pole

North
Pole

Counter
Clock
wise
D
Stator
Surface
ABC
forms
Stator
Surface
CDA
forms
Rotor
Surface
abc
forms
Rotor
Surface
cda
forms
Torque
South
Pole
North
Pole
South
Pole
North
Pole
Clock
wise
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