Use app×
Join Bloom Tuition
One on One Online Tuition
JEE MAIN 2025 Foundation Course
NEET 2025 Foundation Course
CLASS 12 FOUNDATION COURSE
CLASS 10 FOUNDATION COURSE
CLASS 9 FOUNDATION COURSE
CLASS 8 FOUNDATION COURSE
0 votes
307 views
in General by (237k points)
closed by
An alternator having 20 poles and running at 600 rpm will generate alternating voltage and current whose frequency is:
1. 300 Hz
2. 100 Hz
3. 50 Hz
4. 200 Hz

1 Answer

0 votes
by (239k points)
selected by
 
Best answer
Correct Answer - Option 2 : 100 Hz

Concept:

The synchronous speed of an alternator is determined by the frequency of the source and the number of poles.

Derivation:

  • 3-phase supply with a frequency of ‘fs’ is given to the 3-phase distributed winding the rotating magnetic field is set up by the windings.
  •  The speed of the rotating magnetic field is in synchronous with the supply frequency and hence called synchronous speed ‘Ns’ (in rpm).
  • 3-phase windings are wound for a specific even number of poles ‘P’, 2/4/6/8…
  • One cycle of AC current through the windings makes the pole axes move along one pair of poles (P/2).
  • Hence fs cycle per second AC current will give rise to the speed of rotating magnetic field as :

\(\frac{{{N_s}}}{{60}} = \frac{{{f_s}}}{{\frac{p}{2}}}\)  rps.

  • Rearrangement of the above equation will give the equation for synchronous speed in rpm as:

\({N_s} = 120\frac{{{f_s}}}{p}\) rpm.

Calculations:

Given synchronous speed Ns = 600 rpm.

Number of poles p = 20

Frequency, fs = (600 × 20)/120

Frequency, fs = 100 Hertz.

Welcome to Sarthaks eConnect: A unique platform where students can interact with teachers/experts/students to get solutions to their queries. Students (upto class 10+2) preparing for All Government Exams, CBSE Board Exam, ICSE Board Exam, State Board Exam, JEE (Mains+Advance) and NEET can ask questions from any subject and get quick answers by subject teachers/ experts/mentors/students.

Categories

...