Optical Communication Dispersion Quiz
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Questions and Answers

What does dispersion primarily affect in optical communication systems?

  • The color spectrum of the transmitted light
  • The overall power consumption of the system
  • The modulation frequency used in transmission
  • The timing of the signal pulses (correct)

Which of the following is a technique used to mitigate dispersion effects?

  • Frequency modulation schemes
  • Dispersion compensating fibers (correct)
  • Signal amplification modules
  • Pulse shaping algorithms

How does dispersion impact maximum transmission distance?

  • It increases the signal strength over longer distances
  • It decreases the transmission capacity
  • It deteriorates signal quality over distance (correct)
  • It eliminates the need for compensation techniques

What is often sacrificed in order to reduce dispersion effects in optical systems?

<p>Available bandwidth (D)</p> Signup and view all the answers

Why is managing dispersion crucial in optical communication systems?

<p>To ensure reliable and efficient operation (D)</p> Signup and view all the answers

What is a significant advantage of squirrel cage rotors in induction motors?

<p>Simplicity in construction (B)</p> Signup and view all the answers

Which of the following is a disadvantage of squirrel cage rotor motors?

<p>Lower starting torque (C)</p> Signup and view all the answers

What phenomenon occurs due to an improper combination of rotor and stator slots?

<p>Cogging and Crawling (A)</p> Signup and view all the answers

What is the purpose of designing the length of the air gap in induction motors?

<p>To improve cooling efficiency (D)</p> Signup and view all the answers

What is the empirical formula for calculating air gap length in induction motors?

<p>$l_g = 0.2 + 2vDL$ mm (D)</p> Signup and view all the answers

Which rotor type generally exhibits better starting torque?

<p>Slip ring rotor (B)</p> Signup and view all the answers

What effect does a longer air gap have on the magnetizing current?

<p>Increases magnetizing current (B)</p> Signup and view all the answers

What does the presence of odd harmonics in a rotating magnetic field generally cause in induction motors?

<p>Crawling (C)</p> Signup and view all the answers

What is the primary purpose of connecting external resistances to slip rings at starting?

<p>To increase starting torque (B)</p> Signup and view all the answers

What is the maximum allowed flux density in the rotor teeth?

<p>1.5 Tesla (C)</p> Signup and view all the answers

What is a crucial consideration when determining the number of rotor slots?

<p>It should not be equal to the number of stator slots (C)</p> Signup and view all the answers

How is the rotor current calculated in relation to stator current?

<p>Ir = (Kws x Ss x Z's) / (Kwr x Sr x Z'r) (A)</p> Signup and view all the answers

What is the allowed range for current density in rotor conductors?

<p>4 to 6 Amp/mm2 (D)</p> Signup and view all the answers

What determines the size of the rotor slot?

<p>Conductor arrangement based on the stator (D)</p> Signup and view all the answers

What is the safety limit for the voltage between slip rings for medium voltage machines?

<p>400 volts (D)</p> Signup and view all the answers

What should the area of one rotor tooth be calculated based on?

<p>Tooth width and iron length (D)</p> Signup and view all the answers

What is used to limit the total copper loss in a rotor?

<p>Calculating the rotor winding resistance (B)</p> Signup and view all the answers

What effect do the 5th and 7th harmonics have on the magnetic poles compared to the fundamental?

<p>They produce five and seven times the number of poles of the fundamental, respectively. (A)</p> Signup and view all the answers

What is the effect of 7th harmonic on the speed of a three-phase induction motor?

<p>It tends to run the motor at one seventh of its normal speed. (C)</p> Signup and view all the answers

What is the phenomenon called when a motor refuses to run due to improper rotor and stator slot numbers?

<p>Cogging (B)</p> Signup and view all the answers

How can the tendency of cogging be minimized?

<p>By selecting proper rotor slots in relation to stator slots. (C)</p> Signup and view all the answers

What is one consequence of skewing rotor slots?

<p>It increases leakage reactance. (B)</p> Signup and view all the answers

What guideline is used to avoid synchronous hooks in torque-speed characteristics?

<p>Ss - Sr ? ±P, ±2P, ±5P (C)</p> Signup and view all the answers

What is the formula to determine the current per rotor bar in a squirrel cage induction motor?

<p>Ib = (Kws x Ss x Z's) x I'r / (Kwr x Sr x Z'r) (A)</p> Signup and view all the answers

What type of rotor slots are generally preferred for better performance in induction motors?

<p>Semi-closed or closed slots (C)</p> Signup and view all the answers

Which of the following is an effect of using fully closed rotor slots?

<p>Reduced starting current (C)</p> Signup and view all the answers

What is the area of the end ring calculated from, considering the end ring current?

<p>Area = Ie / de (C)</p> Signup and view all the answers

What is the calculated current in the rotor based on the given formula?

<p>343.8 amps (B)</p> Signup and view all the answers

What is the standard conductor size selected for the rotor?

<p>13 mm x 4.5 mm (B)</p> Signup and view all the answers

How is the rotor bar resistance calculated?

<p>Resistance = resistivity x length / area (A)</p> Signup and view all the answers

What is the primary material used for stator windings?

<p>Copper (B)</p> Signup and view all the answers

Which of the following best describes the purpose of rotor windings?

<p>Induce current and create torque (B)</p> Signup and view all the answers

What technique is NOT typically used to measure stator winding resistance?

<p>Slip-ring method (C)</p> Signup and view all the answers

What is the calculated copper loss in rotor bars according to the given equations?

<p>398 watts (B)</p> Signup and view all the answers

What is the effect of dispersion in optical fibers on signal transmission?

<p>Causes signal distortion (D)</p> Signup and view all the answers

What is the role of the stator windings in an electric motor?

<p>Create a magnetic field (D)</p> Signup and view all the answers

What is the main reason for measuring stator and rotor winding resistance?

<p>To analyze electrical characteristics (A)</p> Signup and view all the answers

Flashcards

Squirrel Cage Rotor

A type of induction motor rotor with copper or aluminum bars embedded in slots.

Slip Ring Rotor

Induction motor rotor with star-connected three-phase windings.

Air Gap Length

The space between the stator and rotor, critical for motor performance.

Cogging

Undesirable phenomenon in induction motors caused by incorrect stator/rotor slot numbers.

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Crawling

Induction motor running at a very slow speed due to unwanted harmonic components in the rotating magnetic field.

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Rotor Slots

The slots in the rotor where the bars or windings are located.

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Magnetizing Current

The current component in the induction motor that creates the magnetic field.

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Air Gap Length Formula

An empirical formula to determine the optimal or minimum air gap: lg = 0.2 + 2vDL mm

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Harmonics in Induction Motor Flux

Harmonic components in the magnetic flux wave of an induction motor affect its torque-speed characteristics.

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7th Harmonic Effect

The 7th harmonic flux in an induction motor causes a dip in the torque-speed curve at 1/7th of the motor's normal speed.

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Cogging in Induction Motors

An effect where improper rotor and stator slot numbers cause the motor to refuse to move.

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Rotor Slot Skewing

Skewing rotor slots helps to reduce cogging, torque defects, and noise in induction motors.

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Proper Rotor Slot Selection

Selecting the number of rotor slots based on the stator slot number to avoid cogging and other torque-related issues.

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Rotor Bar Current

The current flowing through the rotor bars of a squirrel cage motor, calculated using the stator and rotor parameters and their winding factors.

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Rotor Bar Cross-Sectional Area

Calculated based on the rotor bar current and a chosen current density, affecting rotor resistance and losses.

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Rotor Slots (Shape)

Semi-closed or closed slots with narrow openings are preferred for rotor slots to improve motor performance.

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Copper Losses in Rotor Bars

Losses estimated from rotor bar length, resistance, and current, influencing motor efficiency.

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End Ring Current

Current flowing through the end rings connecting the rotor bars, crucial for motor operation.

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Optical Dispersion

The spreading of light pulses in optical fibers, causing signal distortion.

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Wound Rotor Induction Motor

An induction motor with external resistors connected to slip rings for adjustable starting torque.

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Rotor Slots

Number of slots in the rotor should not equal stator slots. Proper number to avoid issues like cogging and crawling, keeping tooth width within limits.

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Dispersion Effects on IM Systems

Dispersion in optical fibers degrades signal quality, limiting data rates, transmission distance, and requiring compensation techniques in intensity modulation systems.

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Rotor Turns Calculation

Calculated based on safety considerations (safe voltage) from induced rotor voltage compared to stator voltage and winding factors.

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Compensation Techniques

Methods used to mitigate the effects of dispersion in optical communication systems, including specialized fibers, modules, or signal processing; these add complexity and cost to the system.

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Rotor Current Calculation

Calculated using amp-turns balance between stator and rotor winding and factors like winding and slot dimensions.

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Transmission Distance Limitation

Increased dispersion reduces the maximum distance optical signals can travel reliably, impacting long-haul communication systems.

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Rotor Conductor Area

Calculated based on assumed current density in rotor conductor and its calculated current. Choose shape and size based on area.

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Dispersion-Bandwidth Tradeoff

Increasing bandwidth often worsens dispersion, while reducing dispersion usually decreases bandwidth; careful balance is needed for optimal system performance.

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Rotor Slot Sizing

Design considerations for rotor slots based on conductor size, arrangements, and depth/width ratio (3:4 usually).

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Total Copper Loss

Calculated using mean turn length, number of rotor turns, and rotor winding resistance.

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Flux Density in Rotor Tooth

Critical calculation. Needs to be around 1.8 Tesla. Dimensioning slots depends on this.

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Depth of Stator Core

Calculated based on rotor core flux density (1.2 to 1.4 Tesla), and stator core area.

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Rotor Inner Diameter

Calculated from outer diameter, air gap, and depth of stator core below slots.

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Rotor Bar Resistance

The electrical resistance of the rotor bars in an induction motor.

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Rotor Bar Size

Dimension (area) of the conductors used in the rotor bars, determined based on current density.

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Stator Windings

Stationary coils in electric motors/generators that produce a rotating magnetic field.

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Rotor Windings

Coils (or bars for squirrel cage) on the rotor that interact with the stator field.

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Current Density

Current flowing per unit area (e.g., amps/mm²).

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Copper Loss

Energy dissipated as heat in rotor or stator windings due to resistance.

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Rotor Bar Length

The length of the conductor bar in the rotor slot.

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Induction Motor Performance

The overall effect of stator and rotor resistances, current density on the performance of an induction motor (e.g. Efficiency, torque).

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Stator Winding Resistance

Resistance encountered by current in the stator windings of an electric motor or generator.

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Rotor Winding Resistance

Resistance to current through the rotor windings of motors.

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