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Determine the fault current in the system following a double line to ground short circuit fault at the terminal of a star connected synchronous generator operating initially on an open circuit voltage of 1.0 pu. The positive, negative, and zero sequences reactance of the generator are, respectively j0.35, j0.25, and j0.20, and the star point is isolated from the ground.
  • a)
    -2.165 pu
  • b)
    -2.887 pu
  • c)
    -3.75 pu
  • d)
    -5 pu
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
Determine the fault current in the system following a double line to g...
Here star point is isolated so the flow of fault current is not possible in neutral or ground ( also zero sequence current is zero because zero-sequence current flow through the ground and here the ground is not available) so current is absent in neutral but current available in phase so this fault is considered as line to line  (L-L) fault.
Positive sequence current (i1) for L-L fault is given by;
i1 = voc/(x1 + x2)
Where;
voc = open circuit voltage, x1 = Positive sequence reactance, x2 = Negative sequence reactance
Fault current (if) for L-L fault is given by:
if = √3 × i1
Calculation:
Given that:

voc = 1.0 pu, x1 = j0.35, x2 = j0.25 pu, xo = 0.20pu, xn = ∞ pu  (since Neutral is isolated from ground)
Here, voc = Open circuit voltage, x1 = Positive sequence reactance, x2 = Negative sequence reactance, xo = Zero sequence reactance, xn = Neutral reactance
Here L-L (line to line) fault happened so we will first calculate positive sequence current (i1) then calculate fault current (if) by help of positive sequence current.
Calculation of Positive sequence current (i1);
 i1 = 1/(j0.35+j0.25)
i1 = -j1.6666 pu
So fault current (if) ;
if = √3 × i1
If = -j2.887 pu
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Determine the fault current in the system following a double line to ground short circuit fault at the terminal of a star connected synchronous generator operating initially on an open circuit voltage of 1.0 pu. The positive, negative, and zero sequences reactance of the generator are, respectively j0.35, j0.25, and j0.20, and the star point is isolated from the ground.a)-2.165 pub)-2.887 puc)-3.75 pud)-5 puCorrect answer is option 'B'. Can you explain this answer?
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Determine the fault current in the system following a double line to ground short circuit fault at the terminal of a star connected synchronous generator operating initially on an open circuit voltage of 1.0 pu. The positive, negative, and zero sequences reactance of the generator are, respectively j0.35, j0.25, and j0.20, and the star point is isolated from the ground.a)-2.165 pub)-2.887 puc)-3.75 pud)-5 puCorrect answer is option 'B'. 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 Determine the fault current in the system following a double line to ground short circuit fault at the terminal of a star connected synchronous generator operating initially on an open circuit voltage of 1.0 pu. The positive, negative, and zero sequences reactance of the generator are, respectively j0.35, j0.25, and j0.20, and the star point is isolated from the ground.a)-2.165 pub)-2.887 puc)-3.75 pud)-5 puCorrect answer is option 'B'. 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 Determine the fault current in the system following a double line to ground short circuit fault at the terminal of a star connected synchronous generator operating initially on an open circuit voltage of 1.0 pu. The positive, negative, and zero sequences reactance of the generator are, respectively j0.35, j0.25, and j0.20, and the star point is isolated from the ground.a)-2.165 pub)-2.887 puc)-3.75 pud)-5 puCorrect answer is option 'B'. Can you explain this answer?.
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