APTRANSCO 2012 KEY

1.

1.       A voltage waveform v(t)= 12 t² 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-----------(4t³)

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 90⁰ 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^-2tu(t).to produce a response of

te^-2tu(t), the input must be equal to--------(e-^2t u(t))

8.       The no of roots on the equation 2s⁴+s³+3s²+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 100/30⁰ v, and bus 2 voltage is 100/0⁰ 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/V²).

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------(30⁰)

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+30⁰)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)

61.     Find out y=-----------------(P+Q+R+S)