Electrical Engineering questions For PSU jobs

Electrical Engineering questions For PSU jobs
Solved Electrical Engineering for Career as Electrical engineering freshers in PSUs
Free CElectrical Engineering Sample Paper For PSU Jobs like SAIL BHEL IOC
1. A single line to ground fault occurs on a three- phase isolated neutral system with a line to neutral voltage of V kV. The potentials on the healthy phases rise to a value equal to
(a) √2 V k V
(b) √3 V kV
(c) 3 V kV
(d) 1/ √3VkV

Ans:-D




2. A one kilometer long 11 k V 3-core three-phase metal sheathed cable gave the following test results:
(i) Capacitance between 2 conductors joined to sheath and the third conductor: 0.6 µ F
(ii) Capacitance between all the three conductors bunched together and sheat: 0.96 µF
The effective capacitance of each core to neutral is
(a) 0.l2µF
(b) 0.14µF
(c) 0.16 µF
(d) 0.32 µ F

Ans:-B


3. If the current is 3000 A, for an I.D.M. T. relay with a plug setting of 50% and C. T. ratio of 400 / 5, the plug setting multiplier would be
(a) 7.5
(b) 15.0
(c) 18.75
(d) 37.5

Ans:-B




4. A balanced star-connected load with impedances. of 20 —30 Ohm is supplied from a beta phase, 4-wire, 173 volt system, the voltages to neutral being 100 —90°, 100 30° and 100 150°
The current in the neutral wire is
(a) 5 A
(b) 8.65 A
(c) Zero
(d) 50 A

Ans:-D


5. Two coils in differential connection have self- inductance of 2 mH and 4 mH and a mutual inductance of 0.15 mH. The equivalent inductance of the combination is
(a) 5.7mH
(b) 5.85mH
(c) 6mH
(d) 6.l5mH

Ans:-A



6. Two wattmeters connected to measure the power in a 3-phase balanced delta connected load read W1= 12 kW and W2 = 15 kW respectively. If the same load is reconnected in star, then the wattmetets would read
(a) W1 = 8.66 kW, W2 = 6.93 kW
(b) W1 = 6.93 kW, W2 = 8.66 kW
(c) W1 = 5kW, W2 = 4kW
(d) W1= 4kW, W2 = 5kW

Ans:-C


7. When compared to a first-order low-pass filter, a second-order low-pass filter has
(a) Lower voltage gain
(b) Higher voltage gain
(c) Faster drop in filter response
(d) Higher cut-off frequency

Ans:-D





8. Match List I with List II and select the correct answer using the codes given below the lists:
List I
(Hybrid parameters)
A. h11
B. h22
C. g11
D. g22
List II
(Relation with immittance parameters)
1. 1 / Y11
2. 1 / Z 22
3. 1 / Z 11
4. 1 / Y 22
Codes:
A B C D
(a) 12 3 4
(b) 3 2 1 4
(c) 1 4 3 2
(d) 3 4 1 2

Ans:-B




9. To improve stability and time response of a control system, poles are often added to the system transfer function. In this context which
one of the following pairs is correctly matched?
(a) Zero poles ...make the system stable and slow responding
(b) One pole ... makes the system less stable and slow responding
(c) Two poles ...make the system less stable and fast responding
(d) Three poles ... make the system conditionally stable and fast responding

Ans:-C


10. Consider the following statements regarding root loci:
1. All root loci start from the respective poles of G(s) H(s).
2. All root loci end at the respective zeros of G(s) H(s) or go to infinity.
3. The root loci are symmetrical about the imaginary axis of the s-plane.
Of these statements:
(a) 1, 2 and 3 are correct
(b) 1 and 2 are correct
(c) 2 and 3 are correct
(d) 1 and 3 are correct

Ans:-B



11. Consider the following statements:
Addition of resistance to the rotor of a two-phase ac servomotor will
1. Increase the overall torque.
2. Increase the stability of operation.
3. Linearize its torque-speed characteristics.
4. Lead to attainment of maximum stalling torque
Of these statements:
(a) 1, 2 and 4 are correct
(b) 2, 3 and 4 are correct
(c) 2 and 3 are correct
(d) 1, 3 and 4 are correct

Ans:-C




12. A 6-pole lap-connected dc generator with 480 conductors has an armature resistance of 0.06 ohm. If the conductors are reconnected to form a wave winding, other things remaining unchanged, the value of the armature resistance will be
(a) 0.01 ohm
(b) 0.06 ohm
(c) 0.36 ohm
(d) 0.54 ohm

Ans:-D


13. A 2-pole series motor with its two field coils connected in series runs at a speed of 500 rpm. If the field coils ar reconnected in parallel and assuming that the torque is constant and the magnetic circuit is unsaturated, the new speed will be
(a) 250 rpm
(b) 500/ √2rpm
(c) 500 √rpm
(d) 1000 rpm

Ans:-D


14. Consider the following statements:
As a 3-phase induction motor is loaded from no- load to rated load,
1. there is an improvement in the power factor.
2. the torque increases almost in proportion to slip.
3. the air-gap flux falls sharply.
Of these statements:
(a) 1,2 and 3 are correct 4
(b) 1 and 2 are correct
(c) 2 and 3 are correct
(d) 1 and 3 are correct

Ans:-B


15. Short-circuit ratio of a synchronous machine is the ratio of the
(a) open-circuit voltage to the short-circuit current at a given excitation
(b) short-circuit current to the open-circuit voltage at a given excitation
(c) excitation current required for the rated voltage on open-circuit to the excitation current required for the rated armature current under short-circuit
(d) excitation current required for the rated
armature current under short-circuit to the excitation current required for rated voltage on open-circuit

Ans:-C

16. In a 3-phase induction motor, the angular speed of the stator field is ω and, the actual angular speed of the rotor is w r’, and the stator induced emf is given by es = NI, ω K ws Ø sin ωt, (N1 being the stator turns/phase), the rotor emf with N2 as the rotor/turns phase will be (K ws = stator winding factor and K wr =. rotor winding factor)
(a) e r = N2 ω K W r sin ω t
(b) e r =N2 ω r K wr sin ωr t
(c) e r = N2 (ω - ωr) Kωr Ø sin(ω —r)t
(d) e r = N2 ( ω+ ωr) K ωrØ sin (ω + ω r) t

Ans:-A


17. A 3-phase induction motor requires a starter
(a) because there is no back emf induced in the stator winding during starting
(b) because the motor does not possess an inherent starting torque
(c) because the induced secondary voltage and hence the currents in the windings are abnormally high during starting
(d) to increase the starting torque

Ans:-C


18. For a rotor-fed 3-phase induction motor, the absolute speed of the rotating magnetic field in space is
(a) the synchronous speed
(b) the difference between the synchronous speed and the rotor speed
(c) the rotor speed
(d) zero

Ans:-A


19. A synchronous machine connected to infinite bus bars is initially delivering active power to and absorbing lagging reactive power from the bus bars. As increase in the power input to the synchronous machine will cause
(a) an increase in both armature current and power factor
(b) an increase in armature current and a decrease in power factor
(c) a decrease in both armature current and power factor
(d) a decrease in armature current and an increase in power factor.

Ans:-A




20. The introduction of interpoles in between the main poles improves the performance of a dc machine, because
(a) the interpoles produce additional flux to augment the developed torque
(b) the flux waveform is improved with reduction in harmonics
(c) the inequality of air-gap flux on the top and bottom halves of the armature is removed
(d) a counter-emf is induced in the coil undergoing commutation

Ans:-C


21. For proper synchronisation of a large synchronous machine to a bus, the frequency of the-incoming machine
(a) should be exactly the same as that of the bus
(b) should be slightly higher than that of the bus
(c) should be slightly lower than that of the bus
(d) can be of any value

Ans:-B


22. A 3-phase alternator delivers power to a balanced 3-phase load of power factor 0.707 lagging. It is observed that the open-circuit emf phasor leads the corresponding terminal voltage phasor by 15°. Neglecting the effect of harmonies, the angle between the axis of the main field mmf and the axis of the armature mmf will be
(a) 300 electrical
(b) 60° electrical
(c) 90° electrical
(d) 150° electrical

Ans:-B


23. A 3-phase, 400 V, delta connected alternator has a synchronous impedance of (0+j20) ohms per phase. If it delivers a balanced load of 12 WA at zero power factor leading, then the percentage ‘voltage regulation of the alternator
is equal to
(a) —50
(b) +50
(c) —150
(d) +150

Ans:-C


24. If the height to width ratio of the window of core- type transformer is increased, then
(a) its leakage reactance and percentage voltage regulation will decrease
(b) its leakage reactance and percentage voltage regulation will increase
(c) its leakage reactance will be unaffected but total space in the window will increase to accommodate the windings better
(d) efficiency will increase and temperature rise will decrease

Ans:-A




25. A 220 / 110V, 50 Hz single-phase transformer having a negligible winding resistances operates from a variable voltage, variable frequency supply such that V I/f (V1 = primary applied voltage, f = source frequency) is constant. This will bring in, in the given range of frequencies,
(a) variation in both eddy current loss and hysteresis loss
(b) variation only in the eddy current loss, hysteresis loss remaining constant
(c) variation only in the hysteresis loss, eddy current loss remaining constant
(d) no change either in the eddy current loss or the hysteresis loss

Ans:-A


26. On direct on line (DOL) starting, dc motor is found to rotate in the direction opposite to that for which it was designed. The motor is a
(a) series motor
(b) shunt motor
(c) cumulatively compounded, motor
(d) differential compounded motor

Ans:-D



27. Consider the following statements:
To control the speed of a dc shunt motor above the base speed over a reasonably wide range, the motor must
1. have compensating winding
2. have interpole winding.
3. be started using a 3-point starter.
4. be started using a 4-point starter.
Of these statements:
(a) l, 2and 4arecorrect
(b) 1, 2 and 3 are correct
(c) 1 and 3 are correct
(d) 2 and 4 are correct

Ans:-A


28. Consider the following types of drives:
1. Slip energy recovery schemes with converter cascade in the rotor circuit.
2. Stator voltage control using ac voltage controller.
3. Constant V/f control (V = applied voltage, f = frequency).
4. Variable voltage and variable 7requency schemes with air-gap flux constant.
Those suitable for blowers and centrifugal pumps (T α N²) include
(a) l, 3and 4
(b) l, 2 and3
(c) l, 2 and 4
(d) 2, 3 and4

Ans:-B


29. In the case of a thyristor, di /dt capability can be improved by
(a) thermal triggering
(b) voltage triggering
(c) dV / dt triggering
(d) gate pulse triggering

Ans:-A








30. A 3-phase overhead transmission line has its conductors horizontally spaced with spacing between adjacent conductors equal to ‘d’ If, now, the conductors of the lines are rearranged to form an equilateral triangle of sides equal to ‘d’, then the
(a) average capacitance as well as average inductance will increase
(b) average capacitance will decrease but the average inductance will increase
(c) average capacitance will increase but the average inductance will decrease
(d) surge impedance loading of the lines will increase

Ans:-C