The starting current of a 15 hp, 460 v, 3 phase induction motor is 130 A. What voltage in volts should be applied to the motor so that the starting current will not exceed 84.8 A.
A238
B295
C300
D310
Electrical Engineering · Question Bank
3P Induction Motors
115 of 135 questions match · page 3 of 6. Answer in your head first, then check the solution.
Which one is a method of stopping an electric motor by momentarily reversing its connection to the supply?
AJogging
BInching
CSequencing
DPlugging
In a three-phase induction motor, copper bars are sometimes placed deep in the rotor. This is done for what reason?
ATo improve the efficiency of the motor
BTo improve the starting torque
CTo reduce the copper loss
DTo reduce the rotor reactance
In a wound rotor motor, the rotor winding is wound for a number of poles ____ that of the stator windings.
AEqual to
BLess than
CGreater than
DAny of these
Which of the following is the primary reason why an induction motor is more preferred than a dc motor?
AIt provides a much higher starting torque
BIt has a simple and rugged construction
CIt provides more fine speed control
DAll of these
How do you call the phenomenon in a squirrel cage induction motor showing tendency to run at very low speed?
ASkewing
BDamping
CCogging
DCrawling
How can the starting torque of a three-phase induction motor be increased? +
ABy increasing the rotor resistance
BBy increasing the rotor reactance
CBy increasing the supply frequency
DBy using a star-delta starter
An induction motor at no load is similar to a transformer with the ____.
ASecondary being short circuited
BSecondary being open circuited
CLow voltage winding being open circuited
DLow voltage winding being short circuited
A three-phase wound motor is otherwise called what motor?
ASynchronous motor
BSlip ring motor
CSeries motor
DStepper motor
What is the slip of an induction motor at standstill?
AZero
BOne
CInfinity
DUndefined
A three-phase induction motor is running at half of its rated load. What will happen if one of the line fuses gets opened?
AThe motor will immediately stop running
BThe motor will continue to run at the same speed
CThe motor will continue to run at slightly lesser speed
DThe motor will continue to run at an increased speed
Two induction motors A and B are identical except that the air gap of A is 50% greater than that of B. Which of the following statements is true?
AThe no-load pf of A is better than that of B
BThe no-load pf of A is poorer than that of B
CThe core losses of A are more than those of B
DThe operating flux of A will be smaller than that of B
A very large 3-phase induction motor is started using which of the following?
AStar-delta starting
BDOL starting
CAutotransformer starting
DPart winding starting
What is the effect of the magnetizing current drawn by an induction motor to its operating power factor
AIt makes the pf lagging
BIt makes the pf leading
CIt makes the pf unity
DIt makes the pf zero
The term “cogging” is normally associated to what type of motors?
AInduction motor
BDC series motor
CDC shunt motor
DRepulsion motor
The speed of an induction motor is comparable to which of the following dc motors?
ASeries motor
BShunt motor
CLong shunt compound motor
DShort shunt compound motor
The stator and rotor cores of an induction motor are made up of magnetic materials. Why?
ATo keep the cost of construction low
BTo make the parts strong
CTo reduce the magnetizing current
DTo increase the reluctance of the magnetic path
The slip rings for induction motors are made from which of the following materials?
AAluminum
BPhosphor bronze
CCarbon
DCobalt steel
Which one is true about the power factor of a squirrel cage induction motor?
AIt is low at light loads only
BIt is low at heavy loads only
CIt is low at rated load only
DIt is low at any loads
What is the reason why it is advisable to avoid direct on line starting of a large induction motor?
AThe starting torque is too high
BThe motor might run in the wrong direction
CThe motor will pick up speed dangerously
DThe motor takes dangerously high current
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