(Solved)For an induction motor under operating condition, the EMF in d-axis phase in rotor circuit is ______ its standstill rotor induced EMF per phase.

A) equal to
B) s times
C) (1 − s) times
D) 1/s times

---

✅ Answer:

➡️ B) s times

---

🧠 Detailed Solution

◆ Step 1: Key Concept

➡️ Rotor EMF depends on relative speed between RMF and rotor

➡️ This relative speed is represented by slip (s)

---

◆ Step 2: At Standstill

→ Rotor speed = 0
→ Slip $s=1$

➡️ Induced EMF is maximum

$$E_2=E_{20}$$

(where $E_{20}$ = standstill rotor EMF)

---

◆ Step 3: At Running Condition

→ Rotor speed increases
→ Slip decreases

➡️ Induced EMF reduces proportionally

$$E_2=s\times E_{20}$$

---

◆ Step 4: Interpretation

➡️ EMF ∝ relative speed
➡️ Relative speed ∝ slip

Hence:

➡️ Rotor EMF = s times standstill EMF

---

❌ Why Other Options Are Incorrect

◆ A) equal → Only at standstill (s = 1)
◆ C) (1 − s) → Related to speed, not EMF
◆ D) 1/s → Opposite relation

---

🔑 Key Points to Remember

◆ Rotor EMF: $E_2=s{E}_{20}$
◆ At standstill → $s=1\Rightarrow E_2=E_{20}$
◆ At synchronous speed → $s=0\Rightarrow E_2=0$
◆ EMF decreases as motor accelerates

---

🎯 Final Conclusion

➡️ Rotor EMF under operating condition =
s × (standstill EMF) ✔️