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WorksheetsElectrical Machines- II
Total questions: 50
Worksheet time: 17mins
What is the operating principle of an alternator?
Ohm's Law
Lenz's Law
Faraday's Law
Colomb's Law
In a power plant, where is the rotor generally placed:
Rotor
Stator
Exciter
Shaf
Which of the following is an advantage of a rotating field system?
Reduces weight of the alternator
Easy insulation of armature winding
Provides better cooling
All of the above
A cylindrical rotor alternator is preferred for:
Low speed applications
High speed applications
Medium speed applications
None of the above
What is the EMF equation of a power generation?
E=4.44fTΦKdKpE = 4.44 f T \Phi K_d K_p
E=2fTΦE = 2 f T \Phi
E=1.1fTΦE = 1.1 f T \Phi
E=3.14fTΦKdKpE = 3.14 f T \Phi K_d K_p
Based on the alternator, the relationship between frequency (f), speed (N), and poles (P):
f=NP60f = \frac{N P}{60}
f=60PNf = \frac{60 P}{N}
f=NPf = \frac{N}{P}
f=PNf = \frac{P}{N}
Pitch factor is used to:
Increase harmonics
Reduce harmonics
Reduce voltage
Increase spread
Which type of coolant is used for large transformers?
Air cooling
Water cooling
Hydrogen cooling
Oil cooling
What is the function of an alternator's exciter?
Provides mechanical power
Supplies DC to the field winding
Generates AC voltage
Reduces losses
Where are the best transformers used:
High-speed applications
Low-speed applications
Medium-speed applications
None of the above
The electric field configuration of a charge is:
When charge is removed
When speed increases
When wavelength increases
When excitation is removed
What is known as the simultaneous opposition method?
EMF method
MMF method
JPF method
Direct method
In an alternator, the armature reaction in the integrated power function:
Magnetizing
Demagnetizing
Cross-magnetizing
None of the above
Which test evaluates the compliance resistance of a converter production?
Open loop test
Closed loop test
Load test
Both
Electric voltage regulation can be negative, the power factor:
Leading
Lagging
Unity
Zero
Which method provides the most accurate voltage regulation?
EMF method
MMF method
ZPF method
Uniform resistance method
The main reason for using damper coils in alternators:
To improve efficiency
To reduce harmonics
To prevent hunting
To increase power factor
What factor affects the organization of the electric potential of a power?
Charge
Excitation
Power factor
All of the above
To determine the performance of an alternator:
Open circuit test
Short circuit test
Load test
All of the above
What happens when the thrust in an alternator increases?
Power outage increases
Power factor decreases
Speed increases
Torque increases
What creates a rotating magnetic field in a three-phase induction motor?
Single-phase supply
Three-phase supply
DC supply
Static magnets
Slip in an induction motor is defined as:
Difference between stator and rotor speed
Ratio of rotor speed to stator speed
Ratio of synchronous speed to rotor speed
Ratio of difference in speed to synchronous speed
How is a squirrel cage rotor identified:
High starting current
Wound coils and birds
Short-circuited copper or aluminum bars
Output resistance control
When an induction motor operates at steady state, its torque-slip characteristics are:
Unstable region
Negative slip region
Low-slip region
High-slip region
The efficiency of a three-phase induction motor:
Is lower than DC motors
Is higher than single-phase motors
Is not load-dependent
Is always 100%
Which method can be used to control the speed of an induction motor?
Voltage control
Rotor resistance control
Frequency control
All of the above
What is the disadvantage of a slip ring induction motor compared to a squirrel cage motor?
High starting current
More maintenance due to brushes
Low slip
Simpler construction
Cogging in an induction motor occurs due to:
High resistance of the rotor
Harmonic effects
Rotor not starting due to alignment with stator slots
Overloading
What is the suitable starting method for a small squirrel cage induction motor?
Star-Delta starting
Direct-On-Line (DOL) starting
Auto-Transformer starting
Rotor Resistance starting
What is the function of a double-cage rotor in an induction motor?
Improving starting current
Increasing efficiency
Reducing losses
Decreasing starting current
What is the reason for a single-phase induction motor not starting automatically?
Lack of rotating magnetic field
High starting current
Low power factor
High efficiency
In which state of India is the Kanchipuram district located?
Tamil Nadu
Kerala
Karnataka
Andhra
The main purpose of a capacitor-start motor's capacitor:
To improve power factor
To increase efficiency
To provide phase shift for starting current
To reduce electricity
In a shaded pole motor, the rotating magnetic field is created by:
Capacitors
Shading coils
Output resistors
DC excitation
Which motor is used in a ceiling fan?
Universal Motor
Capacitor Start Motor
Shaded Pole Motor
Repulsion Motor
For what purpose is the global electric motor designed to operate:
Only AC
Only DC
For both AC and DC
High frequency AC
A common cause for the failure of an induction motor:
Low voltage
High temperature
High efficiency
Low slip
In motor maintenance, the use of vacuum filling is for:
Reducing the component
Improving performance
Increasing power efficiency
Enhancing starting electricity
The purpose of achieving a stable equilibrium in an induction motor:
Reduce noise and vibrations
Increase efficiency
Reduce core losses
Improve torque
What is the main advantage of a shaded pole motor?
High efficiency
Low cost and simplicity
High starting torque
High speed
A synchronous motor always runs at:
Variable speed
Below synchronous speed
At synchronous speed
Above synchronous speed
What method is generally used to start a synchronous motor?
Direct-On-Line (DOL) starting
Rotor resistance starting
Damper winding starting
Capacitor starting
A singarone motor's V-curve shows the relationship between:
Power and speed
High quality and armature electricity
Power cut and electricity
Vibration and torque
In a balanced electrical machine, to reduce hunting:
Thyristor bars
Output resistors
High-speed operation
Load reduction
Which of the following is a correct application of electric motors?
Air compressors
Writers
Large industrial loads
All of the above
A permanent magnet DC motor does not require:
DC excitation
AC power
Rotor winding
Stator winding
Which of the following is a special AC motor?
Switched Reluctance Motor
Induction Generator
Linear Induction Motor
All of the above
Where are linear induction motors generally used:
Trains and transportation systems
Ceiling fans
Refrigeration appliances
Washing machines
How is the speed of an AC servo motor controlled?
Changing the voltage
Changing the frequency
Changing the load
Both a and b
The switch reluctance motor operates on:
Magnetic attraction between rotor and stator
Capacitive effects
Resistance variation
Synchronization operation
