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The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What should be the minimum value of the earthing resistance to protect 90% of winding?
  • a)
    2.12 Ω
  • b)
     
    1.12 Ω
  • c)
    4.24 Ω
  • d)
    3.24 Ω
Correct answer is option 'A'. Can you explain this answer?
Most Upvoted Answer
The neutral of the three phase 20 MVA, 11kV alternator is earthed thro...
% winding protected = 76.4 %
resistance required to protect 90% of the winding
10 = Is x RV x 100
R = 2.12 Ω.
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Community Answer
The neutral of the three phase 20 MVA, 11kV alternator is earthed thro...
The minimum value of the earthing resistance can be determined using the formula:

Rmin = (1/3) * (Iunb * CT ratio / 2)

Where:
Rmin = minimum value of earthing resistance
Iunb = out of balance current (1.5 A)
CT ratio = current transformer ratio (100/5)

Substituting the given values into the formula:

Rmin = (1/3) * (1.5 * 100/5 / 2)
Rmin = (1/3) * (30 / 2)
Rmin = (1/3) * 15
Rmin = 5 ohms

Therefore, the minimum value of the earthing resistance should be 5 ohms to protect 90% of the winding.
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The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What should be the minimum value of the earthing resistance to protect 90% of winding?a)2.12 Ωb)1.12 Ωc)4.24 Ωd)3.24 ΩCorrect answer is option 'A'. Can you explain this answer?
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The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What should be the minimum value of the earthing resistance to protect 90% of winding?a)2.12 Ωb)1.12 Ωc)4.24 Ωd)3.24 ΩCorrect answer is option 'A'. Can you explain this answer? for Electrical Engineering (EE) 2024 is part of Electrical Engineering (EE) preparation. The Question and answers have been prepared according to the Electrical Engineering (EE) exam syllabus. Information about The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What should be the minimum value of the earthing resistance to protect 90% of winding?a)2.12 Ωb)1.12 Ωc)4.24 Ωd)3.24 ΩCorrect answer is option 'A'. Can you explain this answer? covers all topics & solutions for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What should be the minimum value of the earthing resistance to protect 90% of winding?a)2.12 Ωb)1.12 Ωc)4.24 Ωd)3.24 ΩCorrect answer is option 'A'. Can you explain this answer?.
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