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Electrical Engineering Objective Questions { Induction Motors }

337.  If the load on a squirrel-cage induction motor, operating on a constant voltage, constant frequency ac supply is increased, then
A. power factor angle will increase and slip will decrease
B. power factor angle will decrease and slip will increase
C. both power factor angle and slip will decrease
D. both power factor angle and slip will increase
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338.  A 3-phase 4-pole slip-ring induction motor is supplied with appropriate voltage at 50 Hz to its stator and voltage at 10 Hz to its rotor through slip-rings. The phase sequence of both the voltages is same. The motor will produce steady torque at a sped of
A. 1500 rpm
B. 1200 rpm
C. 300 rpm
D. zero
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339.  The rotor of a 4-pole 3-phase cage induction motor is replaced by a 3-phase, 4-pole wound rotor. When fed with normal supply, the machine will
A. not run
B. run at very low speed
C. run at slightly lower than normal speed
D. run at slightly higher than normal speed
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340.  Consider the following steps 1CSE 19941 (I) Raversing connections to the terminals of the capacitor (2) Changing the position of the capacitor from auxiliary winding circuit to main winding circuit (3) Reversing supply connection to the main winding (4) Reversing supply connection to the auxiliary circuit While installing a new ceiling fan, if the fan motor is found to be rotating in the wrong direction, then the direction of rotation of the motor can be corrected by
A. 1,2 and 3
B. 1, 2 and 4
C. 1,3 and 4
D. 2, 3 and 4
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341.  A 3-phase induction motor operates on a variable frequency, variable voltage supply such that V/f is constant. The breakdown torque of the drive will
A. decrease with decrease in frequency
B. remain constant irrespective of the frequency
C. be slightly lower at very low frequencies
D. increase with decrease in frequency
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342.  A 3-phase stator and rotor winding of a slip-ring induction motor is fed by 3-phase ac supply at a frequency f. If the rotor speed is Nr and synchronous speed is Ns, then the absolute speed of resultant flux in space is
A. N. irrespective of rotor speed Nr
B. (Ns + Nr) if the flux rotates in the same direction as the rotor
C. (Ns _Nr) if the flux rotates in the same direction as the rotor
D. Nr, irrespective of Ns
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343. A 3-phase induction motor draws 1000 kVA at a pf of 0.8 lag. A synchronous condenser is connected in parallel to draw an additional 750 kVA at 0.6 pf lead. The pf of the total load supplied by the mains is
A. unity
B. 0.707 lag
C. 0.707 lead
D. zero
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