Learn the detailed construction of Alternator (Synchronous Generator) with explanation of stator, rotor, and a comparison between Salient Pole and Cylindrical Rotor types. Best for SSC JE, RRB JE, GATE, and Electrical Exams.
🌀 What is an Alternator?
An alternator, also known as a synchronous generator, is an electrical machine that converts mechanical energy into electrical energy in the form of alternating current (AC). It works on the principle of electromagnetic induction.
⚙️ Construction of Alternator
The alternator consists of two main parts:
1. Stator (Stationary Part)
- Function: Contains armature winding where EMF is induced.
- Construction:
- Made of laminated steel to reduce eddy current losses.
- Three-phase winding placed in slots of stator core.
- Winding is generally connected in star configuration.
2. Rotor (Rotating Part)
- Function: Carries the field winding which is excited by DC supply.
- Types of Rotors:
- Salient Pole Rotor
- Cylindrical (Non-Salient) Rotor
🔁 Working Principle of Alternator
When the rotor’s field winding is excited with DC, it produces a rotating magnetic field. As the rotor spins, this magnetic field cuts across the stator conductors, inducing an alternating EMF according to Faraday’s Law. The EMF is sinusoidal and three-phase in nature.
🧩 Types of Rotor in Alternator
1. Salient Pole Rotor
- Structure: Poles project outward from rotor surface.
- Speed: Suitable for low-speed operation.
- Applications: Used in hydroelectric power stations.
- Poles: Typically 4, 6, 8, 12, or more.
2. Cylindrical Rotor
- Structure: Smooth cylinder with field windings in slots.
- Speed: Suitable for high-speed operation.
- Applications: Used in thermal and nuclear power stations.
- Poles: Typically 2 or 4 poles.
📊 Comparison: Salient Pole vs Cylindrical Rotor
| Feature | Salient Pole Rotor | Cylindrical Rotor |
|---|---|---|
| Shape | Projected poles on rotor surface | Smooth cylinder with slots |
| Speed | Low (100–1500 RPM) | High (1500–3000 RPM) |
| No. of Poles | 4, 6, 8, 12 or more | 2 or 4 |
| Applications | Hydroelectric power stations | Thermal/nuclear power stations |
| Air Gap | Non-uniform | Uniform |
| Rotor Diameter | Large | Small |
| Axial Length | Short | Long |
| Inertia | Less | High |
| Cooling | Air-cooled | Hydrogen/Forced air cooled |
| Efficiency | Comparatively Lower | Higher |
| Construction | Simple | Precise and Complex |
| Maintenance | Easy | Precision required |
🧠 Remembering Tip for Exams
"Salient → Slow → Hydro"
"Cylinder → Speedy → Thermal"
📌 Key Points for SSC JE & RRB JE Exams
- Alternator works on Faraday’s Law.
- Stator → Armature winding (stationary).
- Rotor → Field winding (rotating).
- Salient pole → Hydro → Low-speed.
- Cylindrical rotor → Thermal → High-speed.
📚 FAQs on Alternator Construction
❓ What are the main parts of an alternator?
Answer: The main parts are the stator and rotor.
❓ Which rotor type is used in high-speed alternators?
Answer: Cylindrical rotor is used in high-speed alternators.
❓ Why is the stator kept stationary in an alternator?
Answer: It avoids high-current transfer through slip rings and provides mechanical stability.
❓ What are the advantages of rotating field over rotating armature in alternator?
❓ Why do salient pole alternators have more poles?
Answer: They run at lower speeds, so more poles are needed to maintain the same frequency.
🔎 Search Description
Learn the complete construction of alternator or synchronous generator, with stator, rotor and comparison between salient and cylindrical pole rotor. Best for SSC JE, RRB JE, GATE EE, and other competitive exams.
🏷️ Tags
alternator construction, synchronous generator, salient pole vs cylindrical rotor, stator rotor, ssc je electrical, rrb je electrical, electrical machines, hydro vs thermal alternator