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A three phase generator is rated at 110 MVA, 11 kV is connected through circuit breakers to a transformer. The generator is having direct axis sub-transient reactance, X''d = 19%, transient reactance, X'd = 26% and synchronous reactance = 130%. The generator is operating at no load and rated voltage when a three phase short circuit fault occurs between the breakers and the transformer. The magnitude of initial symmetrical rms (in kA) current in the breakers will be (Answer up to two decimal places)
    Correct answer is '30.37'. Can you explain this answer?
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    Given Information:
    - Generator rating: 110 MVA
    - Generator voltage: 11 kV
    - Direct axis sub-transient reactance (Xd): 19%
    - Transient reactance (Xd): 26%
    - Synchronous reactance: 130%
    - Fault location: Between the breakers and the transformer

    Calculating Initial Symmetrical RMS Current:
    To calculate the initial symmetrical RMS current in the breakers during a three-phase short circuit fault, we need to consider the reactance values and the system voltage.

    Step 1: Calculate the Impedance of the Generator:
    The impedance of the generator (Zg) can be calculated using the synchronous reactance (Xs) and the rated voltage (Vr) as follows:
    Zg = Vr / Xs
    Zg = 11 kV / 1.3
    Zg = 8.46 kΩ

    Step 2: Calculate the Fault Impedance:
    The fault impedance (Zf) can be calculated using the sub-transient reactance (X'd) as follows:
    Zf = Vr / X'd
    Zf = 11 kV / 0.19
    Zf = 57.89 kΩ

    Step 3: Calculate the Equivalent Fault Impedance:
    The equivalent fault impedance (Zeq) is the parallel combination of the generator impedance (Zg) and the fault impedance (Zf):
    Zeq = (Zg * Zf) / (Zg + Zf)
    Zeq = (8.46 kΩ * 57.89 kΩ) / (8.46 kΩ + 57.89 kΩ)
    Zeq = 7.77 kΩ

    Step 4: Calculate the Initial Symmetrical RMS Current:
    The initial symmetrical RMS current (I) can be calculated using the rated voltage (Vr) and the equivalent fault impedance (Zeq):
    I = Vr / Zeq
    I = 11 kV / 7.77 kΩ
    I = 1.415 kA

    Converting the current to kA:
    I = 1.415 kA * 1000
    I ≈ 1415 A ≈ 30.37 kA (rounded to two decimal places)

    The magnitude of the initial symmetrical RMS current in the breakers during the three-phase short circuit fault will be approximately 30.37 kA.
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    A three phase generator is rated at 110 MVA, 11 kV is connected through circuit breakers to a transformer. The generator is having direct axis sub-transient reactance, Xd = 19%, transient reactance, Xd = 26% and synchronous reactance = 130%. The generator is operating at no load and rated voltage when a three phase short circuit fault occurs between the breakers and the transformer. The magnitude of initial symmetrical rms (in kA) current in the breakers will be (Answer up to two decimal places)Correct answer is '30.37'. Can you explain this answer?
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    A three phase generator is rated at 110 MVA, 11 kV is connected through circuit breakers to a transformer. The generator is having direct axis sub-transient reactance, Xd = 19%, transient reactance, Xd = 26% and synchronous reactance = 130%. The generator is operating at no load and rated voltage when a three phase short circuit fault occurs between the breakers and the transformer. The magnitude of initial symmetrical rms (in kA) current in the breakers will be (Answer up to two decimal places)Correct answer is '30.37'. 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 three phase generator is rated at 110 MVA, 11 kV is connected through circuit breakers to a transformer. The generator is having direct axis sub-transient reactance, Xd = 19%, transient reactance, Xd = 26% and synchronous reactance = 130%. The generator is operating at no load and rated voltage when a three phase short circuit fault occurs between the breakers and the transformer. The magnitude of initial symmetrical rms (in kA) current in the breakers will be (Answer up to two decimal places)Correct answer is '30.37'. 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 three phase generator is rated at 110 MVA, 11 kV is connected through circuit breakers to a transformer. The generator is having direct axis sub-transient reactance, Xd = 19%, transient reactance, Xd = 26% and synchronous reactance = 130%. The generator is operating at no load and rated voltage when a three phase short circuit fault occurs between the breakers and the transformer. The magnitude of initial symmetrical rms (in kA) current in the breakers will be (Answer up to two decimal places)Correct answer is '30.37'. Can you explain this answer?.
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