At steady-state characteristics of a DC series motor, which of the following statements are correct?

I) The speed-torque relationship of a DC series motor is non-linear.

II) Both the armature current and the field current of a DC series motor decrease with increasing load torque.

III) The efficiency of a DC series motor is generally higher compared to DC shunt motor.

IV) The efficiency of a DC series motor is generally lower compared to DC shunt motor.

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  1. Statements I, II and IV are correct
  2. Only statements I and IV are correct
  3. Statements I, II and III correct
  4. Only statements I and III are correct

Answer (Detailed Solution Below)

Option 2 : Only statements I and IV are correct
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Detailed Solution

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I) The speed-torque relationship of a DC series motor is non-linear: TRUE

गति (N) बनाम बलाघूर्ण (Ta) विशेषता गति (N) बनाम धारा (Ia) के समान है क्योंकि बलाघूर्ण की विशेषता चुंबकीय संतृप्ति तक धारा के वर्ग के लिए आनुपातिक है और चुंबकीय संतृप्ति के बाद धारा के समानुपाती है।

F1 Nakshatra Madhuri 18.08.2021 D20

  • यह स्पष्ट है कि श्रेणी मोटर कम गति पर उच्च बलाघूर्ण विकसित करती है और इसके विपरीत।
  • ऐसा इसलिए है क्योंकि बलाघूर्ण में वृद्धि के लिए आर्मेचर धारा में वृद्धि की आवश्यकता होती है, जो कि क्षेत्र धारा भी है।
     

II) Both the armature current and the field current of a DC series motor decrease with increasing load torque.: FALSE

Torque (Ta) [Load] vs Current (Ia) Characteristic:

हम जानते हैं कि:

Ta ∝ ϕIa

चुंबकीय संतृप्ति तक, ϕ ∝ Ia

ताकि, Ta ∝ \(I_a^2\)

चुंबकीय संतृप्ति के बाद, ϕ स्थिर है

ताकि Ta ∝ Ia

F1 Nakshatra Madhuri 18.08.2021 D21

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