面试题与答案

An induction motor operates on the principle of electromagnetic induction, where a rotating magnetic field induces current in the rotor, causing it to rotate.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Stepper motors provide precise control over angular displacement, exhibit high torque at low speeds, and do not require feedback for position control.

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.

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.

The main field winding in a synchronous generator produces the magnetic field necessary for inducing voltage in the stator windings as the rotor rotates.

A governor in a hydroelectric generator controls the flow of water to the turbine, regulating the generator's speed and ensuring stable power output.

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.

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.

A choke (inductor) in a fluorescent lamp ballast limits the current flowing through the lamp, ensuring proper operation and preventing excessive current.