(Solved) In an induction motor under running condition, the rotor reactance per phase is ______ its standstill phase reactance.

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

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✅ Answer:

➡️ A) s times

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🧠 Detailed Solution

◆ Step 1: Key Concept

➡️ Rotor reactance depends on rotor frequency

$$X_2=2\pi f_{r}L$$

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◆ Step 2: Rotor Frequency Relation

$$f_r=s\times f$$

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◆ Step 3: Substitute in Reactance

$$X_2=2\pi (sf)L=s(2\pi fL)$$$$X_2=s{X}_{20}$$

Where:
→ $X_{20}$ = standstill reactance

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◆ Step 4: Interpretation

➡️ At standstill → $s=1\Rightarrow X_2=X_{20}$
➡️ At running → $s<1\Rightarrow X_2<X_{20}$

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❌ Why Other Options Are Incorrect

◆ B) equal → Only at standstill
◆ C) 1/s → Opposite relation
◆ D) (1 − s) → Not related to reactance

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🔑 Key Points to Remember

◆ Rotor reactance: $X_2=s{X}_{20}$
◆ Depends on slip (s)
◆ As speed increases → slip decreases → reactance decreases
◆ Maximum reactance at standstill

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🎯 Final Conclusion

➡️ Rotor reactance under running condition =
s × (standstill reactance) ✔️