Questions unit4

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Power System Analysis

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Questions unit4

  1. 1. Unit IV Practice QuestionsQ1. A 50 MVA, 11KV unloaded generator has the following data: Xg0 = 0.04pu, X1 = 0.3pu, X2= 0.25pu, Xn = 0.1pu, Xf = 0.3pu. Find the fault current and the voltage of the healthy line if there is a DLG type of fault on the terminals of the generator which is maintained at 80% of the rated voltage. [2.067KA]Q2. The given figure shows a power network with two generators connected in parallel to a transformer feeding a transmission line. The far end of the line is connected to an infinite bus through another transformer. Star point of each transformer. Generator 1 and infinite bus are solidly grounded. The positive, negative and zero sequence reactance of various components in per unit on a common base are : Positive Negative Zero Generator 1 0.15 0.15 0.08 Generator 2 0.25 0.25 0.06(neutral isolated) Each 0.15 0.15 0.15 Transformer Infinite Bus 0.15 0.15 0.05 Line 0.20 0.20 0.40With both generators and infinite bus operating at 1.0 pu voltage on no load, a line-to-ground fault occursat one of the terminals of the star-connected winding of the transformer A. Calculate the currents flowing in the fault. [-j6.74pu]Q3. For a power system shown in figure below, find the fault current at point F for a SLG type of fault, assuming that the pre- fault current in the circuit is zero : The rating of the components are: machines(generator as well as motor) : 1200KVA, 600V, X1 = X2 = 10% and X0 = 5% Transformers : 1200 KVA, 600/3300V and leakage reactance is 5%
  2. 2. Transmission lines : Reactance is 20% on a base of 1200KVA and 3300VQ4. Determine the fault current, the bus voltages and the line currents during the fault when a 3φ fault occurs with a fault impedance of Z f = j0.16 pu. The negative sequence reactance is same as positive sequence reactance mentioned in the diagram, the zero sequence reactance is 5% and neutral reactance is 4% for both the machines.Q5. For the power system shown in the figure, there is a DLG fault at the point F. Calculate the fault current by taking a base of 100MVA and 11KV in the generator circuit. Rating of generator is 100MVA, 11KV, X1=20%, X2=15% and X0=10%.the voltage at the load point is 60KV prior to the fault. The neutral reactance of the generator is 5% on its rating.. [3.255< 97deg pu]

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