AC Machines: Master Alternating Current Motors and Generators

Question 1

In an induction motor, what is the name of the component that rotates?

Accepted Answer

Rotor

Answer

Stator

Answer

Armature

Answer

Field

Question 2

In an induction motor, the rotating magnetic field is produced by:

Accepted Answer

Alternating current flowing in the stator windings

Answer

Permanent magnets embedded in the rotor

Answer

Direct current flowing in the rotor windings

Answer

Residual magnetism in the stator core

Question 3

The synchronous speed of an AC generator is determined by:

Accepted Answer

The number of poles in the machine and the frequency of the AC supply

Answer

The voltage of the AC supply and the load connected to the generator

Answer

The power factor of the load and the efficiency of the generator

Answer

The type of winding used in the stator and the rotor

Question 4

The power factor of an AC circuit is defined as the ratio of:

Accepted Answer

Real power to apparent power

Answer

Apparent power to real power

Answer

Reactive power to real power

Answer

Real power to reactive power

Question 5

The torque developed by an AC machine is proportional to:

Accepted Answer

The product of the stator and rotor currents

Answer

The square of the stator current

Answer

The difference between the stator and rotor currents

Answer

The ratio of the stator and rotor currents

Question 6

What is the primary function of the damper winding in a synchronous generator?

Accepted Answer

To mitigate hunting

Answer

To enhance starting torque

Answer

To improve voltage regulation

Answer

To optimize power factor

Question 7

What is the intended purpose of employing a star-delta starter for an induction motor?

Accepted Answer

To reduce starting current

Answer

To increase initial torque

Answer

To safeguard the motor against overload

Answer

To enhance power factor

Question 8

Describe the relationship between slip and torque in an induction motor.

Accepted Answer

Slip is inversely proportional to torque.

Answer

Slip is directly proportional to torque.

Answer

Slip is independent of torque.

Answer

Slip is inversely proportional to the square of torque.

Question 9

What is the main purpose of the stator in an AC machine?

Accepted Answer

To create a rotating magnetic field.

Answer

To convert electrical energy into mechanical energy.

Answer

To provide structural support for the rotor.

Answer

To regulate the machine's voltage.

Question 10

Which of the following is NOT a classification of AC machines?

Accepted Answer

DC motor

Answer

Induction motor

Answer

Synchronous generator

Answer

Permanent magnet synchronous motor

Question 11

What is the function of slip in an induction motor?

Accepted Answer

To allow the rotor to rotate at a speed slightly less than the synchronous speed.

Answer

To regulate the torque produced by the motor.

Answer

To enhance the motor's efficiency.

Answer

To minimize the starting current of the motor.

Question 12

What is the purpose of the damper winding in a synchronous generator?

Accepted Answer

To facilitate the synchronization of the rotor with the rotating magnetic field.

Answer

To reduce the generator's starting current.

Answer

To improve the generator's overall efficiency.

Answer

To protect the generator from overloading.

Question 13

Which of the following is NOT a type of AC machine?

Accepted Answer

DC motor

Answer

Induction motor

Answer

Synchronous generator

Answer

Stepper motor

Question 14

Identify the primary difference between an induction motor and a synchronous generator.

Accepted Answer

Induction motors have a rotating magnetic field, while synchronous generators have a stationary magnetic field.

Answer

Induction motors operate at a constant speed, while synchronous generators operate at a variable speed.

Answer

Induction motors are AC motors, while synchronous generators are DC motors.

Answer

Induction motors are more efficient than synchronous generators.

Question 15

What is the primary function of a squirrel-cage rotor in an induction motor?

Accepted Answer

Provide a path for current flow

Answer

Generate a rotating magnetic field

Answer

Reduce starting torque

Answer

Enhance efficiency

Question 16

What key advantage does a synchronous generator possess over an induction generator?

Accepted Answer

Synchronous generators can generate power at a consistent frequency.

Answer

Synchronous generators are inherently more efficient.

Answer

Synchronous generators are more compact than induction generators.

Answer

Synchronous generators are less expensive than induction generators.

Question 17

Which of the following is not a type of AC machine?

Accepted Answer

DC motor

Answer

Induction motor

Answer

Synchronous motor

Answer

Synchronous generator

Question 18

Which component is the core of an induction motor?

Accepted Answer

Stator

Answer

Rotor

Answer

Exciter

Answer

Commutator

Question 19

What is the primary purpose of the damper winding in a synchronous generator?

Accepted Answer

To prevent hunting

Answer

To provide a starting torque

Answer

To increase the efficiency of the generator

Answer

To regulate the output voltage

Question 20

What is the role of the starting capacitor in an induction motor?

Accepted Answer

To provide a starting torque

Answer

To increase the efficiency of the motor

Answer

To reduce the current drawn from the supply

Answer

To regulate the output speed

Question 21

Which of the following is NOT a factor that affects the efficiency of an AC machine?

Accepted Answer

Output power factor

Answer

Copper losses

Answer

Iron losses

Answer

Mechanical losses

Question 22

Describe the function of a damper winding within a synchronous motor:

Accepted Answer

Prevention of oscillations during starting and stopping

Answer

Improvement of motor efficiency

Answer

Regulation of motor speed

Answer

Provision of starting torque

Question 23

Identify the characteristic associated with a squirrel-cage rotor in an induction motor:

Accepted Answer

Elevated starting current

Answer

Reduced starting torque

Answer

Enhanced efficiency

Answer

Improved speed regulation

Question 24

State the primary purpose of a power factor correction capacitor in an AC induction motor:

Accepted Answer

Reduction of reactive power consumption

Answer

Enhancement of motor efficiency

Answer

Improvement of starting torque

Answer

Regulation of motor speed

Question 25

Identify the option that does not represent a type of loss in an AC machine:

Accepted Answer

Capacitive loss

Answer

Copper loss

Answer

Iron loss

Answer

Mechanical loss

Question 26

Which of the following factors does not influence the efficiency of an AC machine?

Accepted Answer

Ambient temperature

Answer

Load factor

Answer

Power factor

Answer

Speed

Question 27

Which of the following is not a type of AC machine?

Accepted Answer

DC motor

Answer

Induction motor

Answer

Synchronous generator

Question 28

What is the primary function of the squirrel cage rotor in an induction motor?

Accepted Answer

To create a magnetic field that interacts with the stator field

Answer

To convert electrical energy to mechanical energy

Answer

To reduce the starting torque of the motor

Question 29

What is the main purpose of a damper winding in a synchronous generator?

Accepted Answer

To prevent hunting

Answer

To improve the starting torque

Answer

To reduce the voltage regulation

Question 30

What is the effect of increasing the field current in a synchronous generator?

Accepted Answer

Increased terminal voltage

Answer

Decreased terminal voltage

Answer

No change in terminal voltage

Question 31

What is a characteristic of a salient-pole synchronous machine?

Accepted Answer

High reluctance torque

Answer

Low reluctance torque

Answer

No reluctance torque

Question 32

Which of the following is NOT a type of AC machine?

Accepted Answer

Stepper motor

Answer

Induction motor

Answer

Synchronous generator

Answer

Synchronous motor

Question 33

What is the primary function of the stator in an AC machine?

Accepted Answer

To produce a rotating magnetic field that interacts with the rotor.

Answer

To convert electrical energy into mechanical energy.

Answer

To carry the armature windings.

Answer

To provide a magnetic path for the flux.

Question 34

What is the main advantage of a synchronous generator over an induction generator?

Accepted Answer

Precise voltage and frequency control

Answer

Higher power density

Answer

Higher efficiency

Answer

Lower cost

Question 35

What is the significance of the power factor in AC machines?

Accepted Answer

It affects the power consumption and efficiency of the machine.

Answer

It influences the speed regulation.

Answer

It has no significant impact.

Answer

It determines the starting torque.

Question 36

What is the purpose of using a variable frequency drive (VFD) with AC motors?

Accepted Answer

To control motor speed and torque.

Answer

To enhance reliability.

Answer

To reduce power consumption.

Answer

To reduce noise.

Question 37

The slip of an induction motor is defined as:

Accepted Answer

The difference between the synchronous speed and the rotor speed, expressed as a percentage of synchronous speed.

Answer

The speed at which the rotor rotates.

Answer

The ratio of the stator current to the rotor current.

Question 38

The rotor of a squirrel-cage induction motor is typically made of:

Accepted Answer

Aluminum or copper bars embedded in a laminated iron core.

Answer

Wound coils.

Answer

Solid steel.

Answer

Permanent magnets.

Question 39

A synchronous generator is able to maintain a constant output frequency because:

Accepted Answer

Its rotor speed is synchronized with the frequency of the AC supply.

Answer

It has a high power factor.

Answer

It has a high efficiency.

Answer

It uses a DC field winding.

Question 40

What is the main purpose of a stator winding in an AC machine?

Accepted Answer

To produce a rotating magnetic field that interacts with the rotor.

Answer

To act as a brake.

Answer

To regulate the speed of the motor.

Answer

To provide a path for the rotor current.

Question 41

A three-phase induction motor is typically preferred over a single-phase motor because:

Accepted Answer

It has higher efficiency and starting torque.

Answer

It is smaller in size.

Answer

It requires less maintenance.

Answer

It is simpler to control.

Question 42

How can the speed of an induction motor be controlled?

Accepted Answer

By varying the frequency of the AC supply.

Answer

By adding a brake.

Answer

By adjusting the rotor resistance.

Answer

By changing the magnetic field strength.

Question 43

Which of the following is a key advantage of a synchronous generator over an induction generator?

Accepted Answer

Ability to operate at a constant frequency.

Answer

Lower cost.

Answer

Higher efficiency.

Question 44

A wound-rotor induction motor is different from a squirrel-cage induction motor because:

Accepted Answer

It has a wound rotor with slip rings and brushes.

Answer

It has a higher starting torque.

Answer

It is smaller in size.

Answer

It is more efficient.

Question 45

You are tasked with selecting an AC motor for a variable-speed application. Which type would be most suitable?

Accepted Answer

An induction motor with variable frequency drive (VFD) control.

Answer

A synchronous motor.

Answer

A stepper motor.