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ElectricalMachine
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What is the Speed of Rotating magnetic field (r.m.f) ├Шs produced in the stator?

A

Variable Speed

B

Synchronous Speed

C

Asynchronous Speed

D

Depends on Load

Correct Answer

тЪЩя╕П TE тАв Technical Concept & PrincipleElectricalMachine
Option B

Synchronous Speed

Quick Summary:

The speed of the rotating magnetic field (r.m.f) produced in the stator of an induction motor is known as synchronous speed. This speed is constant and depends solely on the frequency of the supply voltage and the number of poles in the stator without being affected by the load.

тЪЩя╕ПTETechnical SolutionConcept & Principle
ЁЯТб Explanation

The speed of the rotating magnetic field (r.m.f) produced in the stator of an induction motor is known as synchronous speed. This speed is constant and depends solely on the frequency of the supply voltage and the number of poles in the stator without being affected by the load.

ЁЯФв Key Formulas

Ns=120├ЧfPN_s = \frac{120 \times f}{P}NsтАЛ=P120├ЧfтАЛ тАФ Synchronous speed calculation

тЪЩя╕П Working Principle

Synchronous speed is calculated using the formula Ns=120├ЧfPN_s = \frac{120 \times f}{P}NsтАЛ=P120├ЧfтАЛ, where NsN_sNsтАЛ is the synchronous speed in RPM, fff is the frequency of the supply in Hz, and PPP is the number of poles. The rotating magnetic field is generated by the alternating current in the stator windings, creating a magnetic field that rotates at synchronous speed.

ЁЯУМ Key Points
  • тЦ╕

    Synchronous speed is independent of load.

  • тЦ╕

    It is determined by the supply frequency and number of poles.

тЬЕ Advantages
  • тЦ╕

    Provides constant speed operation.

  • тЦ╕

    Efficient for various industrial applications.

тЭМ Disadvantages / Limitations
  • тЦ╕

    Cannot operate below synchronous speed.

  • тЦ╕

    Requires specific design for speed control.

ЁЯЫая╕П Applications / Uses
  • тЦ╕

    Used in synchronous machines.

  • тЦ╕

    Common in applications requiring precise speed.

ЁЯУД Additional Information
  • тЦ╕

    Standard synchronous speed for 50 Hz supply and 4 poles is 1500 RPM.

  • тЦ╕

    Option A is incorrect because the speed is not variable; it is constant for a given frequency and pole configuration.

ЁЯУК Diagram / Illustration
Synchronous Speed Formula
Ns=120├ЧfPN_s = (120 \times f / P)NsтАЛ=P120├ЧfтАЛ
NтВЫ: Synchronous Speed (RPM)f: Frequency (Hz)P: Number of Poles
тЬЕ

B is correct тАФ The speed of the rotating magnetic field is known as synchronous speed, which is a fixed value based on frequency and number of poles.

Core Concepts Used
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Rotating magnetic field Synchronous speed Induction motors
ЁЯТб EXAM TIP

Understand the relationship between frequency, number of poles, and synchronous speed, as it frequently appears in various engineering problems.

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