Power Systems Objective Questions & Answers – Set 9
Power Systems Objective Questions & Answers
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A transmission line has impedance of (0.005 + j0.05) pu. Find the line at which maximum value of negative DC off set current is produced, if it is applied with V_{m} cosÏ‰t?
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Y bus matrix is a sparse matrix, containing more number of zero elements. So that faster calculation is possible. The Y bus matrix is used for the load flow studies. Z bus algorithm or matrix is used for the fault analysis. Inverse of Y bus matrix gives the Z bus matrix, But Z matrix is a full matrix even though Y bus is a sparse matrix. More time is required for inverse of Z bus matrix if the size of the matrix is more than three.
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Advantage/s of per unit system as compare to absolute system?
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A generator has a rating of 10 MVA, 5 kV has a reactance of 0.02 pu. Find the reactance at a new base values of 50 MVA, 10 kV?
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The per unit impedance of a circuit element is 0.30. If the base kV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be
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The per unit impedance Z(pu) is given by
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If the fault is very nearer to the generator, the fault current is
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The voltage regulation of a line at full load 0.8 power factor is 11. A long transmission line under no load conditions, for a good voltage profile needs
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Per unit of any quantity is defined as
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A transmission line has impedance of (0.005 + j0.05) pu. Find the line at which maximum value of negative DC off set current is produced, if it is applied with V_{m} sinÏ‰t?
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When series reactor is used in generating stations, the fault current magnitude is
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The per unit value of a 2 ohm resistor at 100 MVA and 10 kV base voltage is
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Breaking current is a  value?
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Three generators rated 100 MVA, 11 kV have an impedance of 0.15 pu each. If in the same plant, these generators are being replaced by a single equivalent generator, the effective impedance of equivalent generator will be
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Find the relation between sub transient (X"), transient (X') and synchronous reactance (X) ?
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The angular moment of 10 MVA generator is 0.2. Find the new value of angular moment for 20 MVA base?
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The charging current of a 400 kV line is more than that of a 220 kV line of the same length?
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The load current in short circuit calculations are neglected because
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Operator "a" rotates a vector
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The draw back of NR method as compare to GaussSeidel method is/are?
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Making current is a value?
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Fault calculations using computer are usually done by
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The voltage and current instantaneous values are given as 5 sin (Ï‰t + 30Â°) pu and 2 sin (Ï‰t  15Â°) pu respectively. Find the per unit active power?
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A 10 MVA generator has reactance of 0.2 pu. Find the new reactance value for 50 MVA base?
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For a 500 Hz frequency excitation, a 100 km long power line will be modelled as
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A 20 MVA generator has inertia constant of 0.5 pu. Find new value for 50 MVA base?
If in a line, resistance and reactance are found to be equal and regulation is zero, then load will have
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Which of the following method is/are more reliable?
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A generator has reactances of sub transient (X")= 0.5 pu, transient (X') = 0.8 pu and synchronous reactance (X) = 5 pu. The voltages at these reactances are 1.2 V, 1.1 V and 1 V respectively. Find the corresponding sub transient fault current in pu?