Question

To eliminate the 5th harmonic voltage from the phase voltage of an alternator, the coils should be short-pitched by an electrical angle of:

• A. 30 degree
• B. 36 degree
• C. 72 degree
• D. 18 degree

Hint:

Short-pitching is an effective technique in alternators for minimizing certain harmonics and enhancing the overall waveform quality.

Answer 1

The Correct Option is B

Step 1: In alternators, short-pitching (chorded winding) is applied to reduce harmonics, especially the 3rd, 5th, and 7th harmonics. 
Step 2: The required short-pitching angle (\(\alpha\)) to eliminate a specific harmonic is calculated as: \[ \alpha = \frac{180^\circ}{\text{Harmonic Number}} \] For the 5th harmonic: \[ \alpha = \frac{180^\circ}{5} = 36^\circ \] 
Step 3: Therefore, to remove the 5th harmonic voltage, the coils must be short pitched by 36 degrees.