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Construction of synchronous machine and rotor types
Short answer
The stator core is laminated with three-phase distributed windings. The rotor carries the DC field. Salient-pole rotors have projecting poles, non-uniform air gap, many poles, and are used in low-speed hydro generators. Cylindrical (turbo) rotors are smooth forged steel, have uniform air gap, 2–4 poles, and are used in high-speed steam and gas turbine alternators.
With neat sketch, explain about constructional features of synchronous machine. Discuss different types of rotor and their applications.
A synchronous machine has a stationary armature (stator) and a rotating field system (rotor) excited by DC; the rotor runs at synchronous speed .
+-------------------------+
| stator frame |
| +-------------------+ |
| | stator core with | |
| | 3-ph winding slots| |
| | +-------+ | |
| | | rotor | <-- DC via slip rings
| | | (N/S) | | |
| | +-------+ | |
| +-------------------+ |
+-------------------------+
Stator (armature)
- Frame of cast iron or welded steel supports the core.
- Core of thin silicon-steel laminations (to reduce eddy and hysteresis losses) with slots on the inner surface.
- Three-phase winding, usually double-layer, short-pitched and distributed, placed in the slots; usually star connected.
Rotor and field
The field winding is fed with DC through slip rings and brushes (or a brushless exciter). There are two types of rotor:
| Point | Salient-pole rotor | Cylindrical (non-salient) rotor |
|---|---|---|
| Shape | Projecting poles bolted on a spider | Smooth solid forged-steel cylinder with slots |
| Diameter / length | Large diameter, short length | Small diameter, long length |
| Poles | Many (4 to 60+) | 2 or 4 |
| Speed | Low/medium (100–1000 rpm) | High (1500/3000 rpm) |
| Air gap | Non-uniform | Uniform |
| Damper winding | Fitted in pole faces | Not usually needed |
| Prime mover | Hydraulic turbine, diesel engine | Steam/gas turbine (turbo-alternator) |
| Application | Hydro power plants (e.g. most Nepali hydro plants) | Thermal and nuclear plants |
✓ Answer checked by Claude Sonnet 5.5
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