1️⃣ Increase in no-load speed
2️⃣ Increase in full-load power factor
3️⃣ Increase in magnetizing current
4️⃣ Maximum available torque
✅ Answer (Detailed Solution Below)
✔️ Option 3: Increase in magnetizing current
📖 Detailed Solution
🔹 The air gap forms part of the magnetic circuit.
🔹 Increasing air gap increases magnetic reluctance.
🔹 Higher reluctance requires more magnetomotive force (MMF).
🔹 More MMF means higher magnetizing current.
🔹 Magnetizing inductance decreases.
🔹 Reactive current increases.
🔹 Power factor becomes poorer.
🔹 Magnetic coupling weakens.
👉 Hence, increasing air gap increases magnetizing current.
⚙️ Effect of Increased Air Gap
✔️ Reluctance increases
✔️ Permeability decreases
✔️ Magnetizing inductance decreases
✔️ Magnetizing current increases
✔️ Leakage flux increases
✔️ Power factor decreases
📈 Performance Changes Due to Large Air Gap
🔹 Main flux decreases.
🔹 Leakage flux increases.
🔹 Mutual coupling reduces.
🔹 Slip increases.
🔹 Speed decreases.
🔹 Maximum torque reduces.
❌ Why Other Options are Incorrect
(1) Increase in No-Load Speed ❌
🔹 Increased slip reduces speed.
🔹 Speed decreases, not increases.
(2) Increase in Power Factor ❌
🔹 Magnetizing current is reactive.
🔹 Power factor worsens.
(4) Maximum Available Torque ❌
🔹 Reduced flux lowers torque.
🔹 Breakdown torque decreases.
📌 Additional Information
If Air Gap is Increased:
🔹 Reluctance ↑
🔹 MMF required ↑
🔹 Magnetizing current ↑
🔹 Power factor ↓
🔹 Torque ↓
🔹 Speed ↓
📌 Key Exam Notes
⭐ Air gap ↑ → Im ↑
⭐ Air gap ↑ → PF ↓
⭐ Air gap ↑ → Torque ↓
⭐ Air gap ↑ → Speed ↓
📝 Final Summary
📍 Increasing the air gap increases magnetic reluctance, which raises magnetizing current and reduces power factor and torque.
👉 Hence, Option 3 is Correct.