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ElectricalMachine
PrevNext

For a synchronous motor, Curev A & Curve B representing ___________ & _________ respectively.image

A

Lagging & Leading PF

B

Leading & Lagging PF

C

Lagging & Unity PF

D

Lagging & Lagging PF

Correct Answer

тЪЩя╕П TE тАв Technical Concept & PrincipleElectricalMachine
Option A

Lagging & Leading PF

Quick Summary:

Curve A represents the condition of the synchronous motor at lagging power factor (PF), while Curve B represents it at leading power factor. This illustrates how the motor behaves under different load conditions.

тЪЩя╕ПTETechnical SolutionConcept & Principle
ЁЯТб Explanation

Curve A represents the condition of the synchronous motor at lagging power factor (PF), while Curve B represents it at leading power factor. This illustrates how the motor behaves under different load conditions.

ЁЯФв Key Formulas

P=VIcosтБб╧ХP = VI \cos \phiP=VIcos╧Х тАФ Active Power in an AC circuit

Q=VIsinтБб╧ХQ = VI \sin \phiQ=VIsin╧Х тАФ Reactive Power in an AC circuit

тЪЩя╕П Working Principle

Synchronous motors can operate at leading, lagging, or unity power factors depending on their excitation. At lagging PF, the motor draws reactive power, while at leading PF, it supplies reactive power to the system, leading to different slip and torque characteristics.

ЁЯУМ Key Points
  • тЦ╕

    Synchronous motors can maintain constant speed under various load conditions.

  • тЦ╕

    The power factor affects the overall efficiency of synchronous motors.

тЬЕ Advantages
  • тЦ╕

    Can operate at any power factor by adjusting excitation.

  • тЦ╕

    Higher efficiency compared to induction motors under similar loads.

тЭМ Disadvantages / Limitations
  • тЦ╕

    Requires a separate DC source for excitation.

  • тЦ╕

    Complex control systems needed for stability in certain applications.

ЁЯЫая╕П Applications / Uses
  • тЦ╕

    Used in industrial applications requiring constant speed.

  • тЦ╕

    Common in synchronous condensers for power factor correction.

ЁЯУД Additional Information
  • тЦ╕

    Standard synchronous motors operate at rated frequency and constant speed.

  • тЦ╕

    Option B is incorrect as it suggests leading and lagging PF are not represented accurately.

ЁЯУК Diagram / Illustration
Synchronous Motor Characteristics Lagging PFLeading PF Curve ACurve B
тЬЕ

A is correct тАФ it correctly identifies Curve A as lagging PF and Curve B as leading PF.

Core Concepts Used
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Power Factor Reactive Power Motor Efficiency
ЁЯТб EXAM TIP

Understanding the power factor is crucial for optimizing motor performance in various applications.

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