[Solved] In synchronous alternator, which of the following coils will

Concept

• The Electromotive Force (e.m.f.) generated in a Synchronous Alternator ideally follows a sinusoidal waveform.
• The presence of harmonics (especially the 3^rd, 5^th, and 7^th) causes distortion in the output voltage waveform.
• To obtain a waveform closer to a pure sine wave, designers use specific winding techniques to suppress these unwanted harmonics.

Key Points

Distributed Winding:

• In distributed winding, the coils are spread across several slots per pole per phase rather than being concentrated in a single slot.
• This distribution introduces a distribution factor (K_d), which significantly reduces the magnitude of high-frequency harmonics, making the resultant e.m.f. more sinusoidal.
• It also improves the cooling of the machine by spreading the heat generation.

Short Pitch Coils (Chorded Winding):

• A short pitch coil is one where the coil span is less than the pole pitch (180° electrical).
• By choosing an appropriate pitch factor (K_p), specific harmonics (like the 5^th or 7^th) can be completely eliminated or greatly reduced.
• Short pitching also saves copper in the end connections of the windings.

Conclusion

While concentrated and full pitch windings provide a higher magnitude of induced e.m.f., they contain a significant amount of harmonic distortion. To achieve an e.m.f. waveform that is closer to a sine waveform, the combination of distributed winding and short pitch coils is utilized in synchronous alternators.

Hence, distributed winding in short pitch coils provides an e.m.f. closer to a sine waveform.