📘 DC Machine – Construction & EMF Equation
DC machines convert mechanical energy into electrical energy (generator) or electrical energy into mechanical energy (motor).
🔹 1. Construction
Main parts:- Yoke
- Poles & Pole Shoes
- Field Winding
- Armature Core
- Armature Winding
- Commutator
- Brushes
🔹 2. Working Principle
Based on:- Faraday’s Law (Generator)
- Lorentz Force (Motor)
🔹 3. EMF Equation
Generated EMF:E = (P Φ Z N) / (60 A)
Where: P = Number of poles Φ = Flux per pole (Wb) Z = Total armature conductors N = Speed (rpm) A = Parallel paths Lap winding → A = P Wave winding → A = 2 Very important formula.🔹 4. Example
Given: P = 4 Φ = 0.02 Wb Z = 500 N = 1200 rpm Wave winding → A = 2 Calculate generated EMF. Solution:E = (4 × 0.02 × 500 × 1200) / (60 × 2)
Step-by-step: Numerator = 4 × 0.02 × 500 × 1200 = 48000 Denominator = 120E = 48000 / 120 = 400 V
🔹 5. Important Observations
- EMF proportional to flux
- EMF proportional to speed
- Parallel paths affect voltage
🎯 GATE Important Points
- Remember EMF formula clearly
- Know difference between lap & wave winding
- Speed & flux directly affect EMF
- Used in torque derivation next
EMF ∝ Flux × Speed
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