1️⃣ Heating of motor
2️⃣ Unbalancing of motor shaft
3️⃣ Both (1) and (2)
4️⃣ None of these
✅ Answer (Detailed Solution Below)
✔️ Option 3: Both (1) and (2)
📖 Detailed Solution
🔹 In an induction motor, uniform air gap is essential.
🔹 If the air gap becomes uneven, magnetic field distribution becomes unbalanced.
🔹 This produces Unbalanced Magnetic Pull (UMP).
🔹 UMP pulls the rotor toward the side with smaller air gap.
🔹 This leads to shaft deflection and vibrations.
🔹 Bearings experience extra stress.
🔹 Friction and losses increase.
🔹 Localized high flux density increases core losses.
🔹 Excess heat is produced.
👉 Hence, uneven air gap causes both heating and shaft unbalancing.
⚙️ Effects of Uneven Air Gap
✔️ Unbalanced magnetic pull
✔️ Increased vibration
✔️ Shaft bending
✔️ Bearing wear
✔️ Increased losses
✔️ Motor heating
✔️ Reduced life
🌊 Unbalanced Magnetic Pull (UMP)
🔹 Occurs due to unequal air gap.
🔹 Magnetic force becomes asymmetrical.
🔹 Rotor is attracted to smaller gap side.
🔹 Causes mechanical and electrical problems.
❌ Why Other Options are Incorrect
(1) Heating of Motor ❌
🔹 Only partial answer.
🔹 Shaft unbalancing also occurs.
(2) Unbalancing of Shaft ❌
🔹 Only partial answer.
🔹 Heating is also produced.
(4) None of These ❌
🔹 Incorrect because both effects occur.
📌 Additional Information
Effect of Uneven Air Gap in Squirrel Cage Motor
🔹 Increased vibrations ✔️
🔹 Increased speed ❌
🔹 Increased torque ❌
🔹 Increased current ⚠️ (Secondary effect)
👉 Main effect → Vibrations and UMP
📌 Key Exam Notes
⭐ Uneven air gap → Unbalanced magnetic pull
⭐ Main effects → Heating + Vibration
⭐ Result → Reduced motor life
⭐ Maintenance → Essential for alignment
📝 Final Summary
📍 Uneven air gap causes unbalanced magnetic pull, leading to shaft unbalancing and excessive heating.
👉 Hence, Option 3 is Correct.