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

electrical engineering objective questions

electrical engineering objective questions
Electrical Engineering Questions and Answers
multiple choice questions in electrical engineering

1. A shunt motor is running at its rated speed on rated load. If the field circuit gets suddenly opened
(a) Torque developed by the motor will be almost zero and the motor will stop without causing any damage to the motor
(b) The motor will draw very high armature current but it will continue to drive the load at a reduced speed.
(c) The motor would tend to race to a high speed while driving the load
(d) The motor would draw very high armature current and will stall with consequent damage to the armature

Ans:-B
2. A single-phase alternator has a synchronous reactance of 2 ohms and negligible resistance. If it supplies 10 A to a purely capacitive load at 200 V, then the generated emf will be.
(a) 240 volts
(b) 220 volts
(c) 200 volts
(d) 180 volts

Ans:-D
3. Suppose a synchronous generator connected to an infinite bus it supplying electrical power at unity PF to the bus. If its field current is now increased
(a) Both the active and reactive power output of the generator will remain unchanged
(b) The active power supplied will remain unchanged but the machine will also supply lagging reactive power
(c) The active power supplied will increase and the machine will draw leading reactive power
(d) The active power supplied will decrease and the machine will supply leading reactive power

Ans:-B



4. In the phasor-diagram of a round-rotor synchronous generator, the volt age equations is E f = V t + I e ( r a + j X a ), where E f = excitation voltage, V t = terminal voltage, Ie = armature current at lagging power factor, r a = armature resistance; Xs= synchronous reactance. While remaining synchronized to the bus-bars (infinite bus), f the power input from the prime mover is gradually decreased and finally stopped, it will result in
(a) Reversal of ‘I a’ and E lagging V t
(b) Reversal of I a but E f leading V t
(c) The sign of I a remaining unchanged, but E f leading V t
(d) The sign of I a remaining unchanged, but E f lagging V t

Ans:-C

5. A 3-phase Induction motor has a full-load slip of 3 per cent at normal voltage. Which one of the following will be the value of the slip of the motor if ft develops the same torque theoretically while operating at 110 per cent of its normal voltage?
(a) 2.48%
(b) 0.248%
(c) 0.483%
(d) 4.83%

Ans:-A


6. A 6-pole, 3-phase, 60 Hz Induction motor runs at 1000 rpm developing maximum torque. Rotor resistance per phase is 1.2 ohms. Neglecting stator impedance, then for developing maximum torque, the external resistance to be connected in series with each rotor phase will be
(a) 7.2 ohms
(b) 6 ohms
(c) 1.44 ohms
(d) 1.2 ohms

Ans:-A


7. The capacitor-start single-phase Induction motors develop much larger starting torque in comparison with the “split-phase” motors, because the use of capacitors in the auxiliary winding enables
(a) Provision of larger number of turns in the auxiliary winding
(b) A larger starting current to be drawn from the supply
(c) The torque-slip characteristic in general to get a shape to give a large starting torque
(d) The current division between the main and auxiliary windings to be conducive for the development of large starting torque

Ans:-D
8. If the load of a synchronous motor is increases while keeping the field excitation constant, then
(a) Power factor will increase and power angle will decrease
(b) Power factor will decrease and power angle will increase
(c) Both power factor and power angle will increase
(d) Both power factor and power angle will decrease

Ans:-C


9. A synchronous motor operates as a synchronous condenser when it is
(a) Operated at unity power factor
(b) under-excited
(c) Over-excited
(d) Connected in parallel with condensers

Ans:-C


10. An equipment has 0.8 per unit impedance on a base of 66KV, 100 MVA. It’s per unit impedances on a base of 33 KV, 100 MVA will be
(a) 0.4
(b) 0.8
(c) 1.6
(d) 3.2

Ans:-A


11. In a 3-phase power transformer, 5-limbed construction is adopted to
(a) Suppress the 5th and 7th harmonics
(b) Suppress the 3rd and its multiple harmonics
(c) Suppress all the orders of harmonics
(d) Increase the capacity of the transformer

Ans:-A

12. A transformer has a resistance of 2% and reactance of 4%. Its regulations at 0.8 power factor lagging a leading respectively are
(a) 4 per cent and — 0.8 per cent
(b) —4 per cent and 0.8 per cent
(c) — 0.8 per cent and 4 per cent
(d) 0.8 per cent and —4 per cent

Ans:-A

13. Consider the following statements:
The use of Delta-connected tertiary windings in star-star connected power transformers
1. Makes available supply for single-phase loads.
2. Suppresses harmonic voltages.
3. Allows flow of earth fault current for operation of protective devices
4. Provides low-reactance paths for zeros sequence currents.
Of the statements
(a) 1, 2 and 3 are correct
(b) 1, 3 and 4 are correct
(c) 2 and 4 are correct
(d) 1, 2, 3 and 4 are correct

Ans:-D


14. If dv / dt occurring across a thyristor exceeds its permissible value, then the thyristor will
(a) Remain in the forward blocking state without any damage
(b) Turn on only to get damaged
(c) Turn on but whether it gets damaged or not will depend on the final follow up current
(d) Not turn on but get damaged

Ans:-C



15. In a dc machine, the armature mmf is
(a) Rectangular and directed along the inter- polar axis
(b) Triangular and directed along the inter-polar axis
(c) Triangular and directed along the brush axis
(d) Rectangular and directed along the brush axis

Ans:-C


16. The average load current of a dc chopper feeding a pure resistive load is I amps. If a variable inductance connected in the load circuit Is progressively increased from zero value, keeping the duty ratio unchanged, then the average load current will
(a) Increase starting from 1
(b) Decrease with a starting value of 1
(c) Remain the same at 1
(d) Increase to some highest value of current and then decrease again to 1

Ans:-D

17. Consider the following statements:
The source inductance of an ac to dc line commutated phase controlled converter
1. limits dv / dt capability of thyristors.
2. Causes a voltage drop in the de terminal voltage.
3. Improves the line side power factor.
4. limits the range of firing angles.
5. reduces the line side power factor.
Of these statements
(a) 1, 3 and 4 are correct
(b) 1, 2 and 4 are correct
(c) 2 and 5 are correct
(d) 2, 4 and 5 are correct

Ans:-B




18. When starting a differentially connected compound motor, it Is desirable to short-circuit the series field winding to
(a) Avoid very high starting time
(b) Avoid excessive starting speed
(c) Prevent the motor from starting in the reverse direction
(d) Avoid heavy in-rush of current

Ans:-B

19. A single-phase voltage controller is employed for controlling the power flow from 206 V, 50 Hz source into a load consisting of R = 5 Ω and ω L = 12 Ω The value of maximum mis load current and the firing angle are respectively
(a) 260 / 10.9 A and 00
(b) 20 A and 0°
(c) 20 A and 90°
(d) 260 / 10.9 A and 90°

Ans:-C

20. The number of thyristors required for single- phase to single-phase cycloconverter of the midpoint and for three-phase to three-phase 3-pulse type of cycloconverter are respectively
(a) 4and6
(b) 4and4
(c) 4andl8
(d) None of the above

Ans:-C