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Questions practice unit iv


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Power System Analysis, Symmetrical fault,

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Questions practice unit iv

  1. 1. Unit IV Practice QuestionsQ1. A symmetrical short circuit occurs on the 22KV load bus bar. Find the fault apparent power and thefault current. Choose a base of 150MVA. Also draw the reactance diagram[1.91KA, 73MVA]Q2. A 50 MVA, 11KV, 3 phase alternator was subjected to different types of faults. The fault currentswere: 3 phase fault 1870A,LL fault 2590A and SLG fault 4130A. The alternator is solidly grounded. Findthe per unit values of the 3 phase sequence reactances. [1.403, 0.351, 0.151]Q3. A generator connected through a 5 cycle circuit breaker to a transformer, is rated 100MVA, 18KVwith 19%, 26% and 130% as sub- transient, transient and steady state reactances respectively. It isoperating under no load and rated voltage when a three phase short circuit occurs between the breakerand transformer. Find:(i) The sustained short circuit current [2467](ii) The initial rms current in the breaker [16882](iii) The maximum possible DC component of the short circuit current in the breakerQ4.A 3 phase fault occurs atpoint F. The reactancesare marked in per unitvalues based on 100MVA.Neglecting the pre faultpower and losses,calculate the fault MVA atF. Allow a multiplyingfactor of 1.4.[1430, 2000]