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Electrical Engineering Objective Questions { Power System }

316. An overhead line having a surge impedance of 4002 is connected in series with an underground cable having a surge impedance of 100 U. If a surge of 50 kV travels from the line end towards the line-cable junctions, the value of the transmitted voltage wave at the junction is
A. 30 kV
B. 20 kV
C. 80 kV
D. ?30 kV
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317. The load carrying capability of a long AC transmission line is
B.(a) always limited by the conductor size
C.(b) limited by stability considerations.
D.(c) reduced at low ambient temperatures.
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318. Corona losses are minimized when
A. conductor size is reduced.
B. smooth conductor is reduced.
C. sharp points are provided in the line hardware.
D. current density in conductors is reduced.
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319. In a DC transmission line
A. it is necessary for the sending end and receiving and receiving end to be operated in synchronism.
B. the effects of inductive and capacitive reactances are greater than it n AC transmission line of the same rating.
C. there are no effects due to inductive and capacitive reactances.
D. power transfer capability is limited by stability considerations.
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320. Steady state stability of a power system is the ability of the power system to
A. maintain voltage at the rated voltage level.
B. maintain frequency exactly at 50 Hz.
C. maintain a spinning reserve margin at all times.
D. maintain synchronism between machines and on external tie lines.
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321. In a thermal power plant, the feed water coming to the economiser is heated using
A. H.P. steam
B. L.P. steam
C. direct heat in the furnace
D. flue gases.
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322. For given base voltage and base volt-amperes, the per unit impedance value of an element is x. that will be the per unit impedance value of this element when the voltage and volt-ampere bases are both doubled?
A. 0.5x
C. 4x
D. x
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