A) 2 − s
B) 2 + s
C) 1 + s
D) 1 − s
✅ Answer: A) 2 − s
🧠Detailed Solution:
◆ Step 1: Slip Formula
s = (Ns − Nr) / Ns
◆ Step 2: Before Interchanging Leads
Rotor rotates in same direction as stator field.
Slip: s = (Ns − Nr) / Ns
◆ Step 3: After Interchanging Two Phases
→ Phase sequence reverses
→ Rotating magnetic field reverses direction
→ Rotor continues in same direction due to inertia
◆ Step 4: Relative Speed
Relative speed = Ns + Nr
◆ Step 5: New Slip
s' = (Ns + Nr) / Ns
Substitute Nr = Ns(1 − s):
s' = (Ns + Ns(1 − s)) / Ns
s' = 1 + (1 − s) = 2 − s
❌ Why Other Options Are Incorrect
B) 2 + s → Incorrect formula
C) 1 + s → Incomplete expression
D) 1 − s → Wrong interpretation
🔑 Key Points
◆ Interchanging two phases reverses RMF direction
◆ Rotor continues due to inertia
◆ Relative speed becomes (Ns + Nr)
◆ Slip becomes greater than 1 (plugging condition)
🎯 Final Conclusion
Slip after reversing supply leads = 2 − s
Motor enters plugging (braking) condition