1). The transfer function of a real system, H(s), is given as:
H(s) = As + B/(s2 + Cs + D), where A, B, Cand D are positive constants. This system cannot operate as
(a) low pass filter (b) high pass filter (c) band pass filter (d) an integrator
Answer: (b)
Solution:
With one zero and two poles, the given system cannot be a high pass filter.
2). For an ideal MOSFET biased in saturation, the magnitude of the small signal current gainfor a common drain amplifier is
(a) 0 (b) 1 (c) 100 (d) infinite
Answer: (d)
3). The most commonly used relay, for the protection of an alternator against loss of excitation,is
(a) offset Mho relay (b) over current relay (c) differential relay (d) Buchholz relay
Answer: (a)
Solution:
Off-set Mho relay protects the generator against loss of excitation
4). The valid positive, negative and zero sequence impedances (in p.u.), respectively, for a 220kV, fully transposed three-phase transmission line, from the given choices are
(a) 1.1, 0.15 and 0.08 (b) 0.15, 0.15 and 0.35(c) 0.2, 0.2 and 0.2 (d) 0.1, 0.3 and 0.1
Answer: (b)
Solution:
For transmission line,
5). A charger supplies 100 W at 20 V for charging the battery of a laptop. The power devices,used in the converter inside the charger, operate at a switching frequency of 200 kHz. Whichpower device is best suited for this purpose?
(a) IGBT (b) Thyristor (c) MOSFET (d) BJT
Answer: (c)
Solution:
For higher switching frequencies like 200 kHz, power MOSFET is best suitable.
6). The type of single-phase induction motor, expected to have the maximum power factorduring steady state running condition, is
(a) split phase (resistance start) (b) shaded pole(c) capacitor start (d) capacitor start, capacitor run
Answer: (d)
Solution:
Having a run capacitor [permanent capacitor] can improve the power factor of induction motor
7). A MOD 2 and a MOD 5 up-counter when cascaded together resuls in a MOD _____ counter.(in integer)
Answer: (10)
Solution:
Modulus of a cascaded counter of Mod-M and Mod-N is MN
Hence, modulus of a cascade of Mod-2 and Mod-5 counter = 5 X 2 = 10
8). The frequencies of the stator and rotor currents flowing in a three-phase 8-pole inductionmotor are 40 Hz and 1 Hz, respectively. The motor speed, in rpm, is _____ (round off tonearest integer)
Answer: (585)
Solution:
S = 1/40
Rotor speed
Nr = (1-1/4) (120 x 40/8) = 585 rpm
9). A 3-phase, 415 V**, 4-pole, 50 Hz** induction motor draws 5 times the rated current at rated****voltage at starting. It is required to bring down the starting current from the supply to 2times of the rated current using a 3-phase autotransformer. If the magnetizing impedanceof the induction motor and no-load current of the autotransformer is neglected, then thetransformation ratio of the autotransformer is given by _______ (round off to two decimalplaces).
Answer: (0.6324)
Solution:
When auto-transformer starter is used,
x = 0.6324
10). Consider a 3 x 3 matrix A whose (i, j)-th element, a i,j = (i – j) 3. Then the matrix A will be
(a) symmetric (b) skew-symmetric (c) unitary (d) null
Answer: (b)