GATE Electrical Engineering - Complete Master Library

 

📘 Synchronous Generator – Working Principle & EMF Equation

Synchronous generator converts mechanical energy into electrical energy. It is the primary source of power generation in power plants.

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🔹 1️⃣ Construction

Main parts:

• Stator – 3-phase armature winding
• Rotor – DC excited field winding

Rotor types:

• Cylindrical rotor (Turbo alternator)
• Salient pole rotor (Hydro generator)

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🔹 2️⃣ Working Principle

Mechanical input rotates rotor. Rotor magnetic field cuts stator conductors. According to Faraday’s law → EMF induced. Frequency relation:

f = (P N) / 120

Where: P = number of poles N = speed in rpm

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🔹 3️⃣ EMF Equation

RMS value of generated EMF per phase:

E = 4.44 f Φ T k_w

Where: f = frequency Φ = flux per pole T = turns per phase k_w = winding factor

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🔹 4️⃣ Winding Factor

k_w = k_p × k_d

k_p = Pitch factor k_d = Distribution factor Always less than 1.

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🔹 5️⃣ Example

Given: f = 50 Hz Φ = 0.05 Wb T = 100 k_w = 0.9 Find EMF per phase. Solution:

E = 4.44 × 50 × 0.05 × 100 × 0.9

Step by step: = 4.44 × 50 = 222 = 222 × 0.05 = 11.1 = 11.1 × 100 = 1110 = 1110 × 0.9

E ≈ 999 V per phase

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🔹 6️⃣ Important Observations

• EMF proportional to flux
• EMF proportional to speed
• Frequency depends on speed
• Winding factor reduces EMF slightly

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🎯 GATE Important Points

• Remember E = 4.44 f Φ T k_w
• Know pitch & distribution factor
• Frequency-speed relation very important
• Salient vs cylindrical rotor difference

Alternator = Heart of Power Generation