APTRANSCO 2012 KEY ELECTRICAL

1.

1. A voltage waveform v(t)= 12 t

^{2}is applied across a 1H inductor for t>=0 with initial current through it being zero. The current through the inductor for t>=0 is given by-----------(4t^{3})
2. Two incandescent light bulbs fo 40w and 60w rating
are connected in series across the mains. Then--------(the 40 bulb glows brighter)

3. Given two coupled inductors L1 and L2, their mutual
inductances M satisfies-----(M<=sqrt(L1L2)

4. Consider the star network. The resistance between
terminals A and B with C open 6ohms, between terminals B and C with A open is
11ohms, and between terminals C and A with B open is 9ohms. Then
------------(Ra=2, Rb=4, Rc=7)

5. In a series RLC circuit at resonance, the magnitude
of the voltage developed across the capacitor------( can be greater than the
input voltage, however, it is 90

^{0}out of phase with the input voltage)
6. A two port device is defined by the following pair
of quations:

i1=2v1+v2 and i2=v1+v2 its impedance parameters
(z11, z12, z21, z22) are-----(1,-1,-1,2)

7. The impulse response of an initially relaxed linear
system is e

^{-2t}u(t).to produce a response of
te

^{-2t}u(t), the input must be equal to--------(e-^{2t}u(t))
8. The no of roots on the equation 2s

^{4}+s^{3}+3s^{2}+5s+7=0 that lie in the right half of s plane is-------(2)
9. For a feedback control system of type 2, the steady
state error for a ramp input is-------(zero)

10. The output of a linear time invariant control
system is c(t) for a certain input r(t). if r(t) is modified by passing it
through a block whose transfer function is e-s and then applied to the system,
the modified output of the system would be-----------(c(t-1)u(t-1)

11. The phase lead compensation used to-----(decreases
both rise time and overshoot)

12. Consider two buses connected by an impedance of
(0+j5)ohm. The bus 1 voltage is 100/30

^{0}v, and bus 2 voltage is 100/0^{0}v. the real and reactive power supplied by bus 1, resp are……….(1000w, 268 VAr)
13. For a fixed value of complex power flow in a
transmission line having a sending end voltage V, the real power loss will be
proportional to-----------(1/V

^{2}).
14. During a disturbance on a synchronous machine, the
rotor swings from A to B before finally settling down to a steady state at
point C on the power angle curve. The speed of the machine during oscillation
is synchronous at point(s)--------------------(A and B)

15. A 100 MVA, 11kv, 3 phase 50hz, 8 pole synchronous
generator has an inertia constant H equal to 4 MJ/MVA. The stored energy in the
rotor of the generator at synchronous speed will be---(400MJ).

16. In a biased differential relay the bias is defined
as a ratio of----------(operating coil current and restraining coil current))

17. Resistance switching is normally employed
in------(ABCB)

18. The use of high speed circuit breakers----(improves
system stability)

19. Keeping in view the cost and overall effectiveness,
the following circuit breaker is best suited for capacitor bank
switching---(vacuum)

20. If the reference bus is changed in two load flow
runs with the same system data and power obtained for reference bus taken as
specified P and Q in the latter run----------( the system losses will be
unchanged but complex bus voltages will change.)

21. The gauss seidel load flow method has following
disadvantages. Tick the incorrect statement------( unreliable convergence)

22. The torque speed characteristics of a repulsion
motor resembles which of the following dc motor
characteristic------------(series)

23. Which type of motor is most suitable for computer
printer drive-----(stepper motor)

24. A 4 pole lap wound DC generator has a developed
power of P watts and voltage of E volts. Two adjacent brushes of the machine
are removed as they are worn out. If the machine operates with the remaining
brushes, the developed voltage and power that can be obtained from the machine
are----(E,P/4)

25. A 4 point starter is used to start and control the
speed of a -----------( dc shunt motor with field weakening control)

26. The function of oil in a transformer is-----( to
provide insulation and cooling)

27. The core flux of a practical transformer with a
resistive load------------( is strictly constant with load changes)

28. In a transformer zero voltage regulation at full
load is----(possible at leading pf load)

29. A single phase transformer has a turns ratio of
1:2, and is connected to a purely resistive load. The magnetizing current drawn
is 1 A, and the secondary current is 1A. if core losses and leakage reactance
are neglected, the primary current is-(2.24A)

30. The low voltage winding of a 400/230V, single phase
50hz transformer is to be connected to a 25hz, the supply voltage should
be-------(115V)

31. A 400/100V, 10 KVA two winding transformer is
reconnected as an auto transformer is reconnected as an auto transformer across
a suitable voltage source. The maximum rating of such an arrangement could
be-----(50KVA)

32. When the supply voltage to an induction motor is
reduced by 10%, the maximum torque will decrease by approximately-------(20%)

33. In case of a split phase motor, the phase shift
between currents in the two windings is around------(30

^{0})
34. Starting torque can be obtained in the case of a
single phase induction motor with identical main and auxiliary windings by
connecting-----( a capacitor in series with the auxiliary winding)

35. For a single phase capacitor start induction motor
which of the following statements is valid---( the direction of rotation can be
changed by reversing the main winding terminals)

36. An induction motor having full load torque of 60zNm
when delta connected develops a starting torque of 120Nm. For the same supply
voltage, if the motor is changed to star-connection, the starting torque
developed will be-------(40NM)

37. During hunting of synchronous motor –(damper bar
develops torque)

38. The phase sequence of a three phase alternator will
reverse if -------(the field current remains the same but the direction of
rotation is reversed)

39. The effect of stray magnetic fields on the
actuating torque of a portable instrument is max when the operating filed of
the instrument and the stray fields are-(parallel)

40. A current of -8+6(sinwt+30

^{0})A is passed through three meters. They are a center zero PMMC meter, true rms meter and MI instrument. The respective reading( in A) will be----(-8,10,10)
41. R1 and R2 are the opposite arms of a wheatstone
bridge as are R3 and R, the source voltage is applied across R1 and R3 under
balanced conditions which one of the following is true---(R1=R2R3/R4)

42. A dc potentiometer is designed to measure up to
about 2v with a slide wire of 800mm. a standard cell of emf 1.18v obtains
balance at 6010mm. a test cell is seen to obtain balance at 680mm. the emf of
the test cell is-(1.34v)

43. The minimum number of wattmeters required to
measure3 phase 3 wire or unbalanced power is—(2)

44. A reading of 120 is obtained when a standard
inductor was connected in the circuit of a Q meter and the variable capacitor
is adjusted to a value of 300pF. A lossless capacitor of unknown value C, is
then connected and the same reading was obtained when the variable capacitor is
readjusted to a value of 200pF. The value of Cx in pF is—(100)

45. The two inputs of a CRO are fed with the two
stationary periodic signals. In the X Y mode, the screen shows a figure which
changes from ellipse to circle and back to ellipse with its major axis changing
orientation slowly and repeatedly. The following inference can be made from
this----------(there is a constant but small phase difference between the
signals)

46. SCR can be turned off—( anode current should be
less than holding current)

47. The no. of pn junctions in SCR-----(3)

48. TRIAC is a—(antiparallel thyristors combination)

49. GTO can be turned off-(by using a negative current
pulse)

50. Which type of control is used for controlling the
ac drive by using thyristors--------(integral cycle)

51. In DC choppers the output voltage can be controlled
by using FM technique varying--------( T , Toff constant)

52. In phase control rectifiers the output voltage
ripple can be controlled by—‘(load inductance)

53. Which is not a current controlled
device-----(MOSFET)

54. Inverter function---------(DC to AC with variable
frequency)

55. In phase controlled rectifires free wheeling diode
makes-(load current continuation)

56. Dielectric heating application----(wood)

57. In induction heating the following is abnormally
high--------(frequency)

58. Tractive effect w.r.t driving wheel
axis--------(tangential*)

59. welding transformer sets have-------------(high
current, low voltage)

60. Simplify
x’y’z+x’yz’+xy’z+xyz+xyz’=-------(y’z+yz’+xz)

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