Freshers / Beginner level questions & answers
Ques 1. What is the significance of the term 'slip' in induction motors?
Slip is the difference between the synchronous speed of the rotating magnetic field and the actual speed of the rotor. It determines the rotor speed relative to the rotating magnetic field.
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Ques 2. What is the purpose of laminations in the core of a transformer?
Laminations reduce eddy current losses in the transformer core by minimizing the closed loops for current flow.
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Ques 3. Define torque in the context of electrical machines.
Torque is the measure of the rotational force exerted by a motor. In electrical machines, it is the product of the force applied and the distance from the axis of rotation.
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Ques 4. What is the function of the stator in an electric motor?
The stator provides a stationary magnetic field in electric motors, inducing a magnetic field in the rotor and causing it to rotate.
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Ques 5. What is the difference between a motor and a generator?
A motor converts electrical energy into mechanical energy, while a generator converts mechanical energy into electrical energy.
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Ques 6. Define the term 'flux' in the context of electrical machines.
Flux is the magnetic field generated by the flow of current in a coil. It plays a crucial role in the operation of transformers, motors, and generators.
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Ques 7. What is the role of the armature in an electric generator?
The armature in an electric generator is the rotating part that cuts across magnetic lines, inducing an electromotive force (EMF) in the coils and generating electrical power.
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Ques 8. What is the role of brushes in a DC motor?
Brushes in a DC motor maintain electrical contact between the rotating armature and the stationary part (stator), allowing current to flow into the armature windings.
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Ques 9. Define the term 'horsepower' in the context of electrical machines.
Horsepower is a unit of power measurement, equivalent to 745.7 watts. It is commonly used to express the power output of motors and engines.
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Intermediate / 1 to 5 years experienced level questions & answers
Ques 10. What is the principle of operation of an induction motor?
An induction motor operates on the principle of electromagnetic induction, where a rotating magnetic field induces current in the rotor, causing it to rotate.
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Ques 11. Explain the difference between synchronous and asynchronous machines.
Synchronous machines operate at a constant speed and are synchronized with the supply frequency, while asynchronous machines (like induction motors) don't operate at a fixed speed and may slip from the synchronous speed.
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Ques 12. How does a transformer work?
A transformer works on the principle of electromagnetic induction, where varying current in the primary coil induces a voltage in the secondary coil through a magnetic field, with the turns ratio determining the voltage transformation.
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Ques 13. Explain the concept of power factor in electrical machines.
Power factor is the ratio of real power to apparent power in an electrical system. It indicates the efficiency of power utilization and is crucial for electrical machines.
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Ques 14. What is the role of a commutator in a DC motor?
The commutator in a DC motor reverses the direction of current in the coil windings, ensuring a continuous unidirectional torque and preventing the motor from stalling.
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Ques 15. Explain the concept of slip rings in electrical machines.
Slip rings are conductive rings used in certain rotating electrical machines to maintain electrical connections with the stationary part, allowing for continuous rotation without tangling wires.
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Ques 16. Define the term 'cogging' in the context of induction motors.
Cogging is the phenomenon where an induction motor experiences jerky motion or hesitation at low speeds due to the interaction of rotor slots with the stator magnetic field.
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Ques 17. How does a three-phase induction motor differ from a single-phase induction motor?
Three-phase induction motors have three windings and generate a rotating magnetic field, while single-phase induction motors have only one winding and produce a pulsating magnetic field.
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Ques 18. What is the purpose of a capacitor in a single-phase induction motor?
A capacitor in a single-phase induction motor is used to create a phase shift, producing a rotating magnetic field necessary for starting and running the motor.
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Ques 19. Explain the concept of back emf in DC motors.
Back emf is the voltage induced in the armature of a DC motor due to its rotation. It opposes the applied voltage and is essential for controlling motor speed.
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Ques 20. What is the significance of the synchronous speed in synchronous machines?
Synchronous speed is the speed at which the rotating magnetic field in a synchronous machine travels. It determines the electrical frequency and plays a crucial role in power generation.
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Ques 21. Explain the term 'regenerative braking' in the context of electrical machines.
Regenerative braking is a mechanism in which a motor acts as a generator, converting kinetic energy into electrical energy and feeding it back into the power supply.
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Ques 22. What are the advantages of using a stepper motor?
Stepper motors provide precise control over angular displacement, exhibit high torque at low speeds, and do not require feedback for position control.
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Ques 23. How does a squirrel cage rotor differ from a wound rotor in an induction motor?
A squirrel cage rotor has shorted conductors, while a wound rotor has external resistances connected to its windings. The squirrel cage rotor is simpler and more commonly used.
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Ques 24. Explain the concept of torque-speed characteristics in DC motors.
Torque-speed characteristics depict the relationship between the torque developed by a DC motor and its speed. These curves are essential for motor selection and performance analysis.
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Ques 25. Explain the role of the main field winding in a synchronous generator.
The main field winding in a synchronous generator produces the magnetic field necessary for inducing voltage in the stator windings as the rotor rotates.
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Ques 26. What is the purpose of a governor in a hydroelectric generator?
A governor in a hydroelectric generator controls the flow of water to the turbine, regulating the generator's speed and ensuring stable power output.
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Ques 27. Define the term 'crawling' in induction motors.
Crawling is a phenomenon in induction motors where the motor runs at speeds slightly less than the synchronous speed, causing vibrations and noise. It can be mitigated by using skewed rotor slots.
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Ques 28. Explain the principle of operation of a universal motor.
A universal motor can operate on both AC and DC power. It has a series-wound armature and is commonly used in applications requiring variable speed.
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Ques 29. What is the function of a choke in a fluorescent lamp ballast?
A choke (inductor) in a fluorescent lamp ballast limits the current flowing through the lamp, ensuring proper operation and preventing excessive current.
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