Solved model paper ONGC Class-I Executive Graduate-Trainee Jobs

Solved model paper ONGC Class-I Executive Graduate-Trainee Jobs
Electronics Model Questions For ONGC Graduate Trainees
Free online practice paper ongcindia.com ONGC Recruitment Graduate Trainee

1. The field winding of a 3-phase synchronous motor is short-circuited directly. If a 3-phase balanced voltage is impressed across the stator terminals, then the rotor will
(a) Rotate at. Synchronous speed
(b) Rotate at a speed slightly less than synchronous speed
(c) Rotate at a speed very near to half the synchronous speed
(d) Not rotate at all

Ans:-A

2. The positive, negative and zero sequence currents of a star connected load for phase R are given as
IR1 = (l0-j7) A
IR2 = (5+j15) A
JR9 = (5 —j8) A
The neutral current will be
(a) Zero
(b) (15 + j 24)
(c) (-15- j 24) A
(d) (15 – j 24) A

Ans:-A

3. In a synchronous machine, the electric circuits are armature circuit, field circuit and damper circuit and X d is d-axis synchronous reactance; X d is d-axis transient synchronous reactance and X’ is d-axis sub-transient synchronous reactance. If there is no damper winding, then
(a) X’d = X” d
(b) X’’ d = X d
(c) X’d = X d
(d) X d = X’d = X’d

Ans:-A
4. For a given load, the speed of shaded-pole single- phase induction motor fluctuates slightly because
(a) The speed of the magnetic field is not constant
(b) The magnitude of the magnetic field is not constant
(c) The motor operates at higher value of slips
(d) The motor is used with fluctuating load

Ans:-B


5. Two separate induction motors having 6 poles and 4 poles are cascaded 3-phase, 400 V, 60 Hz is the supply to the motors. The synchronous speeds (in rpm) of cascaded set will be
(a) 720, 1200, 1800 and 2400
(b) 600, 1000, 1500 and 3000
(c) 720, 1200, 1800 and 3600
(d) 600, 1200, 1800 and 2400

Ans:-C

6. A separately excited dc motor is fed from a phase- controlled converter. The motor exhibits poor speed regulation. This is due to the
(a) Inductive voltage drop of the converter and possible discontintious conduction
(b) Harmonics in the armature current
(c) Large inductance of the load current
(d) Poor power factor of the converter

Ans:-A

7. A drive suitable for low-speed high-power reversible application is the
(a) Synchro converter-fed ac drive
(b) Current source inverter-fed ac drive
(c) Voltage source (square wave) inverter-fed drive
(d) Induction motor fed from ac voltage supply

Ans:-C


8. The advantage of dual converter in the circulatory current mode is
(a) The low loss in the converter
(b) That it permits dynamic braking of connected motor
(c) The lower cost of the equipment
(d) Faster response

Ans:-D


9. A six-pulse non-reversible thyritorised 415 V ac converter is controlling a 440 V dc motor. If total drop in the circuit is limited to 10%, then the converter must be locked at an angle of
(a) 30°
(b) 600
(c) 450
(d) 900

Ans:-D

10. Which one of the following statements is correct in connection with Inverters?
(a) Both voltage source inverter and current source inverter require feedback diodes
(b) The current source inverter requires feedback diodes
(c) GTO’s can be used only in the current source inverters
(d) The voltage source inverter requires feedback diodes

Ans:-A

11. Consider a dc to dc converter (chopper) having a load resistance of 10 .0 and an Input voltage of 232 V. If the voltage drop across the converter during ON time is 2 V and the frequency of operation is1 kHz at a duty cycle of 0.4, then the average output voltage of the converter will be
(a) 94.0 V
(b) 92.8 V
(c) 92.0 V
(d) 90.8 V

Ans:-C


12. Match List I (device of thyristor family) with List II (characteristic) and select the correct answer using the codes given below the Lists:
List I
A. Asymmetrical thyristor
B. Amplifying gate thyristor
C. Triac
D. GTO
List II
1. Poor turn-off gain
2. Good di / dt capability
3. Poor reverse blocking capability
4. Good turn-off
Codes:
A B C D
(a) 2 4 1 3
(b) 2 4 3 1
(c) 4 2 3 1
(d) 4 2 1 3

Ans:-B

13. The dv/dt protection of an SCR is achieved by using
(a) RL circuit in series with SCR
(b) RC circuit across SCR
(c) L in series with SCR
(d) RC circuit in series with SCR

Ans:-B
14. Nominal-II model is normally used for evaluating the performance of
(a) Short line
(b) Medium line
(c) Long line
(d) Infinite line

Ans:-C

15. The A, B, C constants of a nominal T-circuit are given as
A = 0.95 / 0.5°
B = 85 / 70° ohm
C = 0.0005 / 90° ohm
If the two terminal voltages are held constants at 66 kV, then the steady-slate stability limit of the line will be
(a) 0.3312 MW
(b) 3.312 MW
(c) 33.12 MW
(d) 331.2 MW

Ans:-C
16. A feeder with reactance of 0.2p.u has a sending- end voltage of 1.2 p. u . If the reactive power supplied at the receiving end of the feeder is 0.3 p. u , the approximate voltage drop in the feeder will be
(a) 0.042 p. u.
(b) 0.052 p.u.
(c) 0.060 p.u.
(d) 0.070 p.u.

Ans:-B


17. Which one of the following matrices reveals the topology of the power system network?
(a) Bus incidence matrix
(b) Primitive impedance matrix
(c) Primitive admittance matrix
(d) Bus impedance matrix

Ans:-C

18. A fault occurring on an end-supplied transmission line is more severe from the point of view of RRRV if it is a
(a) Long line fault
(b) Short line fault
(c) Medium line fault
(d) Generator fault

Ans:-D

19. The insulation strength of EHV lines is mainly governed by
(a) Switching overvoltages
(b) Lightning overvoltages
(c) Power frequency overvoltages
(d) Dynamic overvoltages

Ans:-A


20. The coefficient of reflection for current of an open-ended line is
(a) -1
(b) 1
(c) 0.5
(d) Zero

Ans:-A


21. Which one of the following types of linear couplers is used for extremely reliable high-speed bus protection?
(a) Mutual inductors wound on non-magneic torodial cores
(b) Mutual inductors wound on magnetic torodial cores
(c) Capacitor voltage transformers
(d) Wire-wound resistors

Ans:-C
22. A relay most likely to operate undesirably on power swings is the
(a) Over-current relay
(b) Inverse definite minimum time relay
(c) Mho relay
(d) Reactance relay

Ans:-C

23. The inductance and capacitance of a line are respectively 1.0 H and 0.01 pF. If the
Instantaneous value of interrupted current is 10 A, the voltage across the breaker contacts will be
(a) 125kV
(b) 100kV
(c) 75 kV
(d) 66 kV

Ans:-B

24. Which of the following reason make HRC fuses preferable in power circuits?
1. They have inverse time characteristics.
2. They are consistent in performance
3. They can be selected for proper discrimination.
Select the correct answer by using the codes given below:
Codes:
(a) l and 2
(b) 2 and 3
(c) 1 and 3
(d) 1, 2 and 3

Ans:-C


25. For a 12-pulse operation of HVDC converters, the most troublesome set of harmonics on the ac side is
(a) 23rd and 25 th
(b) 12th and 24th
(c) ll th and l3th
(d) 5th and 7th

Ans:-D