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A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero sequence reactance’s of 0.25 pu, 0.15 pu, and 0.05 pu, respectively. The neutral of the generator is grounded with a reactance so that the fault current for a bolted LG fault and that of a bolted three-phase fault at the generator terminal are equal. The value of grounding reactance is:
  • a)
    1 Ω
  • b)
    1.8 Ω
  • c)
    0.1 Ω
  • d)
    2.18 Ω
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero ...
Values of X1 = 0.2 ohms, X2 = 0.3 ohms, and X0 = 0.05 ohms, respectively. Determine the short-circuit current in each sequence when a bolted 3-phase fault occurs at the generator terminals.

Solution:

Given data:

Line voltage, V = 30 kV
Frequency, f = 50 Hz
Apparent power, S = 50 MVA
Positive sequence reactance, X1 = 0.2 ohms
Negative sequence reactance, X2 = 0.3 ohms
Zero sequence reactance, X0 = 0.05 ohms

The short-circuit current in each sequence can be calculated using the following formulas:

1. Positive sequence current, I1:

I1 = (3V)/(X1√3)

I1 = (3 × 30 × 10^3)/(0.2 × √3)

I1 = 261.62 kA

2. Negative sequence current, I2:

I2 = (3V)/(X2√3)

I2 = (3 × 30 × 10^3)/(0.3 × √3)

I2 = 174.41 kA

3. Zero sequence current, I0:

I0 = (3V)/(X0√3)

I0 = (3 × 30 × 10^3)/(0.05 × √3)

I0 = 1048.05 kA

Therefore, the short-circuit current in each sequence when a bolted 3-phase fault occurs at the generator terminals are:

Positive sequence current, I1 = 261.62 kA
Negative sequence current, I2 = 174.41 kA
Zero sequence current, I0 = 1048.05 kA
Community Answer
A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero ...
Concept:
Fault current for LG fault =
Fault current for three phase fault =
where,
X= Positive sequence reactance
X2 = Negative sequence reactance
X= Zero sequence reactance
Xn = Grounding reactance
Calculation:
Given that,
X1 = 0.25 pu
X2 = 0.15 pu
X0 = 0.05 pu
Fault current for LG fault is 
Fault current for three phase fault,
Given that both the fault currents are equal.
⇒ Xn = 0.1 pu
Base kV = 30 kV
Base MVA = 50 MVA
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A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero sequence reactance’s of 0.25 pu, 0.15 pu, and 0.05 pu, respectively. The neutral of the generator is grounded with a reactance so that the fault current for a bolted LGfault and that of a bolted three-phase fault at the generator terminal are equal. The value of grounding reactance is:a)1 Ωb)1.8 Ωc)0.1 Ωd)2.18 ΩCorrect answer is option 'B'. Can you explain this answer?
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A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero sequence reactance’s of 0.25 pu, 0.15 pu, and 0.05 pu, respectively. The neutral of the generator is grounded with a reactance so that the fault current for a bolted LGfault and that of a bolted three-phase fault at the generator terminal are equal. The value of grounding reactance is:a)1 Ωb)1.8 Ωc)0.1 Ωd)2.18 ΩCorrect 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 A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero sequence reactance’s of 0.25 pu, 0.15 pu, and 0.05 pu, respectively. The neutral of the generator is grounded with a reactance so that the fault current for a bolted LGfault and that of a bolted three-phase fault at the generator terminal are equal. The value of grounding reactance is:a)1 Ωb)1.8 Ωc)0.1 Ωd)2.18 ΩCorrect 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 A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero sequence reactance’s of 0.25 pu, 0.15 pu, and 0.05 pu, respectively. The neutral of the generator is grounded with a reactance so that the fault current for a bolted LGfault and that of a bolted three-phase fault at the generator terminal are equal. The value of grounding reactance is:a)1 Ωb)1.8 Ωc)0.1 Ωd)2.18 ΩCorrect answer is option 'B'. Can you explain this answer?.
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