IOCL Electrical-Engineering-EE

                                       IOCL Electrical Engineering Technical Paper

1. Which one of the following statements is NOT TRUE for a continuous time causal and stable LTI system?
(A) All the poles of the system must lie on the left side of the jω axis.
(B) Zeros of the system can lie anywhere in the s-plane.
(C) All the poles must lie within |s| =1.
(D) All the roots of the characteristic equation must be located on the left side of the jω axis.

2.  A single-phase transformer has no-load loss of 64 W, as obtained from an open-circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both LV and HV windings, the measured loss is 81 W. The transformer has maximum efficiency when operated at 
(A) 50.0% of the rated current. 
(B) 64.0% of the rated current. 
(C) 80.0% of the rated current. 
(D) 88.8% of the rated current.

3.  A bulb in a staircase has two switches, one switch being at the ground floor and the other one at the first floor. The bulb can be turned ON and also can be turned OFF by any one of the switches irrespective of the state of the other switch. The logic of switching of the bulb resembles
(A) an AND gate 
(B) an OR gate 
(C) an XOR gate 
(D) a NAND gate

4.  A band-limited signal with a maximum frequency of 5 kHz is to be sampled. According to the sampling theorem, the sampling frequency in kHz which is not valid is
(A) 5 
(B) 12 
(C) 15 
(D) 20

5.  Leakage flux in an induction motor is 
(A) flux that leaks through the machine 
(B) flux that links both stator and rotor windings 
(C) flux that links none of the windings 
(D) flux that links the stator winding or the rotor winding but not both 

6.  A 4-pole induction motor, supplied by a slightly unbalanced three-phase 50 Hz source, is rotating at 1440 rpm. The electrical frequency in Hz of the induced negative sequence current in the rotor is
(A) 100 
(B) 98 
(C) 52 
(D) 48

7.  The slip of an induction motor normally does not depend on
(A) rotor speed 
(B) synchronous speed
(C) shaft torque 
(D) core-loss component

8.  The bridge method commonly used for finding mutual inductance is
(A) Heaviside Campbell bridge 
(B) Schering bridge
(C) De Sauty bridge

(D) Wien bridge

9.  The output Y of a 2-bit comparator is logic 1 whenever the 2-bit input A is greater than the 2-bit input B. The number of combinations for which the output is logic 1. is
(A)4 
(B)6 
(C)8 
(D)1O

10.  The typical ratio of latching current to holding current in a 20 A thyristor is
(A) 5.0
(B) 2.0
(C) 1.0
(D) 0.5

11. A cylindrical rotor generator delivers 0.5 pu power in the steady-state to an infinite bus through a transmission line of reactance 0.5 pu. The generator no-load voltage is 1.5 pu and the infinite bus voltage is 1 pu. The inertia constant of the generator is 5 MW-s/IvWA and the generator reactance is 1 pu. The critical clearing angle, in degrees, for a three-phase dead short circuit fault at the generator tenninal is
(A) 53.5 
(B) 60.2 
(C) 70.8 
(D) 79.6

12. A three-phase, salient pole synchronous motor is connected to an infinite bus. Ig is operated at no load a normal excitation. The field excitation of the motor is first reduced to zero and then increased in reverse direction gradually. Then the armature current
(A) Increases continuously
(B) First increases and then decreases steeply
(C) First decreases and then increases steeply
(D) Remains constant

13. A 4 – point starter is used to start and control the speed of a
(A) dc shunt motor with armature resistance control
(B) dc shunt motor with field weakening control
(C) dc series motor
(D) dc compound motor

14. A low – pass filter with a cut-off frequency of 30Hz is cascaded with a high-pass filter with a cut-off frequency of 20Hz. The resultant system of filters will function as
(A) an all-pass filter
(B) an all-stop filter
(c) an band stop (band-reject) filter
(D) a band – pass filter

15. A negative sequence relay is commonly used to protect
(A) an alternator
(B) an transformer
(C) a transmission line
(D) a bus bar

16. For enhancing the power transmission in along EHV transmission line, the most preferred method is to connect a
(A) Series inductive compensator in the line
(B) Shunt inductive compensator at the receiving end
(C) Series capacitive compensator in the line
(D) Shunt capacitive compensator at the sending end

17. An ammeter has a current range of 0 – 5 A, and its internal resistance is 0.2Ω . In order to change the range to 0 – 25 A, we need to add a resistance of
(A)0.8Ω in series with the meter
(B) 1.0Ω in series with the meter
(C)0.04Ω in parallel with the meter
(D) 0.05Ω in parallel with the meter

18. A three-phase, 33kV oil circuit breaker is rated 1200A, 2000MVA, 3s. The symmetrical breaking current is
(A) 1200 A
(B) 3600 A
(C) 35 kA
(D) 104.8 kA

19. The characteristic equation of a closed-loop system
s(s+1)(s+3)+k(s+2)=O, k>O. Which of the following statements is true?
(A) Its roots are always real
(B) It cannot have a breakaway point in the range —1 <Re[s]< 0
(C) Two of Its roots tend to infinity along the asymptotes Re[s] = -1
(D) It may have complex roots in the right half plane

20. An SCR is considered to be a semi-controlled device because
(A) it can be turned OFF but not ON with a gate pulse
(B) it conducts only during one half-cycle of an alternating current wave
(C) it can he turned ON but not OFF with a gate pulse
(D) it can be turned ON only during one half-cycle of an alternating voltage wave

21. The two inputs of a CRO are fed with 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. 
(A) The signals are not sinusoidal
(B) The amplitudes of the signals arc very close but not equal
(C) The signals are sinusoidal with their frequencies very close but not equal
(D) There is a constant but small phase difference between the signals

22. The increasing order of speed of data access for the following devices is
(i) Cache Memory 
(ii) CDROM 
(iii) Dynamic RAM
(iv) Processor Registers 
(v) Magnetic Tape 
(A) (v),(ii),(iii),(iv),(i)
(B) (v),(ii),(iii),(i),(iv)
(C) (ii),(i),(iii),(iv),(v)
(D) (v),(ii),(1),(iii) , (iv)

23. A field excitation of 20 A in a certain alternator results in an armature current of 400 A in short circuit and a terminal voltage of 2000 V on open circuit. The magnitude of the internal voltage drop within the machine at a load current of 200 A is
(A)1V 
(B)10V 
(C) 100V 
(D) 1000V

24. The pressure coil of a dynamometer type wattmeter is
(A) highly inductive 
(B) highly resistive 
(C) purely resistive 
(B) purely inductive

25. Out of the following plain categories
(i) Nuclear 
(ii) Run-of-river 
(iii) Pump Storage 
(iv) Diesel
the base load power plants are
(A) (i) and (ii)
(B) (ii) and (iii) 
(C) (i). (ii) and (iv) 
(D) (i),(in) and (Iv)