Electrical Power Systems

Objective Questions 455
108. In terms of ABCD constants, the characteristic impedance of overhead transmission is
I
HG KJ 1
2
(a) A
D
I
HG KJ 1
2
(b) B
C
I
HG KJ 1
2
(c) AB
CD
I
HG KJ 1
2
(d) C
D
109. The units of B and C are respectively
(a) mho, mho (b) ohm, ohm (c) mho, ohm (d) ohm, mho.
110. To increase transmitted power over line,
(a) increase its capacitance (b) increase its line voltage
(c) decrease its line inductance (d) any of these.
111. A long transmission line has value of its A constant as
(a) zero (b) nearly zero
(c) unity (d) nearly equal to unity.
112. When two lines having constants A 1, B 1, C 1, D 1 and A 2, B 2, C 2, D 2 are cascaded in series,
the resultant value of A constant will be
(a) A 1A 2 + B 1C 2 (b) A 1 + A 2 (c) A 1A 2 (d) A 1D 2 + A 2D 1.
113. The cause of transient stability is
(a) alternator loosing its excitation (b) switching ON and O in the line
(c) short circuit fault in the lines (d) all of the above.
114. Corona always causes
(a) insulation failure (b) system faults
(c) radio interference (d) all of these.
115. Corona loss is more in
(a) unstranded conductor (b) ACSR
(c) stranded conductor (d) transposed conductor.
116. Load that depends on the supply frequency is of
(a) fan type (b) heating and welding type
(c) synchronous condenser (d) centrifugal pumps.
117. The inertia constants of two machines are respectively 30 and 42 MJ per MVA. When the
change in frequency due to change in load in first machine is 12 Hz, the change in the
second machine frequency will be
(a) 10 Hz (b) 12 Hz (c) 15 Hz (d) 42 Hz.
118. or cost and safety, the outdoor substations are installed for voltages above
(a)6.6 KV (b) 11 KV (c) 33 KV (d) 132 KV.
119. Lamp flicker in secondary distribution system is controlled by
(a) transformer banking (b) series capacitor
(c) (a) and (b) both (d) induction regulator.
120. Transient stability can be improved by the use of
(a) high inertia machines (b) high speed governors
(c) fast acting voltage regulating system (d) all of the above.
121. When a line to line fault occurs, the SC current of an alternator depends upon its
(a) subtransient reactance (b) transient reactance
(c) short circuit resistance (d) synchronous reactance.
122. Maximum SC current occurs due to
(a) dead short circuit (b) L – L fault
(c) L – G fault (d) L – L – G fault.