Model Questions on Diploma Electrical Engineering

1. In a dc machine, for the same value of f, Z and N, which one of the following statements is correct?
(a) Armature emf is more with wave winding than with lap winding.
(b) Armature emf is less with wave winding than with lap winding.
(c) Armature emf depends on whether the machine is running as a motor or a generator.
(d) Armature emf is the same as long as the flux density in the air gap remains the same.

2. If the gain margin of a certain feedback system is given as 20 dB, the Nyquist plot will cross the negative real axis at the point
(a) s = -0.05
(b) s = -0.2
(c) s = -0.1
(d) s = -0.01

3. A three phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3 sec. The symmetrical breaking current is
(a) 1220 A
(b) 3600 A
(c) 35 kA
(d) 104.8 kA

4. A self-excited dc shunt generator, driven by its prime-mover at the rated speed fails to build up voltage across its terminals at no-load. What reason can be assigned for this?
(a) The field circuit resistance is higher than the critical resistance.
(b) The initial shunt field mmf does not assist the residual magnetism
(c) One of the inter-pole connections is reversed
(d) The brush-axis shifts slightly from the geometrical neutral axis of the machine

5. The no-load speed of a dc shunt motor is given as 1200 rpm, the power developed by the machine will be maximum at a speed of
(a) 1200 rpm
(b) 2400 rpm
(c) 4800 rpm
(d) 600 rpm

6. For an electrically heated temperature controlled liquid heater, the best controller is
(a) Single-position controller
(b) Two- position controller
(c) Floating controller
(d) Proportional-position controller

7. In the thermal power plants, the pressure in the working fluid cycle is developed by
(a) Condenser
(b) super heater
(c) feed water pump
(d) turbine

8. If the temperature is increased, the speed of a series and shunt motor
(a) increases, decreases
(b) both increases
(c) both decreases
(d) decreases, increases

9. A minimum phase system has fourteen poles and two zeros. The shape of its highest frequency asymptote in its Bode plot is
(a) -240 dB/decade
(b) -280dB/decade
(c) -320dB/ Decade
(d) -40 dB/decade

10. For harnessing low variable waterheads, the suitable hydraulic turbine with high percentage of reaction and runner adjustable vanes is
(a) Kaplan
(b) Francis
(c) Pelton
(d) Impeller

11. Which one of the following is not a necessary condition to be satisfied for synchronizing an incoming alternator to an already operating alternator?
(a) Same voltage magnitude
(b) Same frequency
(c) Same prime mover speed
(d) Same phase sequence

12. A 645 MVA, 24 kV synchronous generator is feeding full-load at 0.9 pf lagging at rated voltage. The generator has a synchronous reactance of 1.2 W. Reactive power drawn by load is
(a) 580.5 MVAR
(b) 281 MVAR
(c) 389 MVAR
(d) None of these

13. The torque of a reluctance motor can be effectively increased by
(a) increasing reluctance of the magnetic circuit along the direct axis
(b) decreasing the reluctance of the magnetic circuit along the quadrature axis
(c) increasing the ratio of the quadrature axis reluctance to direct axis reluctance
(d) decreasing the ratio of the quadrature axis reluctance to direct axis reluctance

14. While designing controller, the advantage of pole-zero cancellation is
(a) the system order is increased
(b) the system order is reduced
(c) the cost of controller becomes low
(d) system’s error reduced to optimum levels

15. Under no load conditions, the current in a transmission line is because of
(a) capacitance effect
(b) corona effect
(c) proximity effect
(d) back flow from earth

16. In a shaded-pole induction motor, the rotor runs from the
(a) shaded portion to the unshaded portion of the pole while the flux in the former leads that in the latter
(b) shaded portion to the unshaded portion of the pole while the flux in the former lags that in the latter
(c) unshaded portion to the shaded portion while the flux in the former leads that in the latter
(d) unshaded portion to the shaded portion while the flux in the former lags that in the latter

17. In load flow analysis, the load connected at a bus is represented as
(a) constant current drawn from the bus
(b) constant impedance connected at the bus
(c) voltage and frequency dependent source at the bus
(d) constant real and reactive power drawn from the bus

18. In an induction motor, when the number of stator slots is equal to an integral multiple of rotor slots
(a) There may be a discontinuity in torque-slip characteristics
(b) A high starting torque will be available
(c) The maximum torque will be high
(d) The machine may fail to start

19. If the reference bus is changed in two load flow buses with same system data and power obtained for reference bus taken as specified P and Q in the latter run
(a) the system losses will be unchanged but complex bus voltages will change
(b) the system losses will be changed but complex bus voltages remains unchanged
(c) the system losses as well as complex bus voltages will change
(d) The system losses as well as complex bus voltages will be unchanged

20. Zero sequence currents can flow from a line to transformer bank if the windings are in
(a) grounded star-delta
(b) delta-star
(c) star-grounded star
(d) detla-delta

21. Tick the correct statement:
(a) The negative and zero sequence voltages are maximum at the fault location and decrease towards neutral.
(b) The negative and zero sequence voltages are minimum at the fault point and increase towards neutral.
(c) The negative sequence is maximum and zero sequence is minimum at the fault point and decrease and increase respectively towards the neutral.
(d) The negative sequence and zero sequence currents do not exist at the fault point location.

22. A rotating electrical machine its self-inductances of both the stator and the rotor windings, independent of the rotor position will be definitely not develop
(a) starting torque
(b) synchronizing torque
(c) hysteresis torque
(d) reluctance torque

23. The correct sequence of steps needed to improve system stability is
(a) reduce gain, use negative feedback, insert derivative action
(b) reduce gain, insert derivative action, use negative feedback
(c) insert derivative action, use negative feedback, reduce gain
(d) use negative feedback, reduce gain, insert derivative action.

24. By increasing the transmission voltage to double of its original value, the same power can be dispatched keeping the line loss
(a) Equal to original value
(b) half the original value
(c) double the original value
(d) one- fourth of original value

25. A 3-phase induction motor is driving a constant torque load at rated voltage and frequency. If both voltage and frequency are halved, following statements relate to the new condition if stator resistance, leakage reactance and core loss are ignored.
i. The difference between synchronous speed and actual speed remains same
ii. The airgap flux remains same
iii. The stator current remains same
iv. The p.u. slip remains same
Among the above, current statements are
(a) All
(b) i, ii and iii
(c) ii, iii and iv
(d) i and iv

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26. A cable has inductance of 0.22 mH per km and capacitance of 0.202 mF per km. The surge impedance of the cable is
(a) 28 W
(b) 33 W
(c) 42 W
(d) 50 W

27. A synchronous generator is feeding a zero power factor (lagging) load at rated current. The armature reaction is
(a) magnetizing
(b) demagnetizing
(c) cross-magnetizing
(d) ineffective

28. Equal area criterion gives the information regarding
(a) stability region
(b) absolute stability
(c) relative stability
(d) swing curves

29. Which of the following is the non-linearity caused by servomotor?
(a) Static friction
(b) Backlash
(c) Saturation
(d) None of these

30. Two transformers T1 and T2 have identical ratings. Transformer T1 is designed for flux density of 1.15Wb/m2 and transformer T2 is designed for flux density of 1.45 Wb/m2. From the above information it can be concluded that
(a) both transformers will operate at 0.8 p.f. lagging.
(b) both transformers will have identical losses at full load.
(c) the weight of transformer T1 will be more than that of transformer T2.
(d) the regulation of transformer T1 will be better than that of transformer T2.

31. An amplidyne can give which of the following characteristics?
(a) Constant current
(b) Constant voltage
(c) Constant current as well as constant voltage
(d) Constant current, constant voltage and constant power

32. A synchronous generator having an inertia constant of 6.0 MJ/MVA is delivering power of 1.0 pu to an infinite bus through a purely reactive network. Suddenly a fault occurs reducing the generator output power to zero. The maximum power that could be delivered is 2.5 per unit. The critical clearing angle is
(a) 89.27°
(b) 23.58°
(c) 21.95°
(d) 59.33°

33. In the potier’s triangle, the Potier reactance drop per phase is 22 volts per phase at 88 amperes per phase. The Potier’s reactance per phase is
(a) 0.22
(b) 0.25
(c) 0.30
(d) 0.44

34. If the voltage across the units in a two unit suspension insulator is 60% and 40% respectively of the line voltage, the ratio of capacitance of the insulator to that of its capacitance to earth will be
(a) 0.25
(b) 0.5
(c) 0.65
(d) 0.75

35. While starting a synchronous motor by induction motor action, very high emf is induced in the field. This induced emf may damage the insulation of the field winding and of slip rings. The insulation damage can be prevented by
(a) short-circuiting the field winding by field discharge resistance
(b) splitting the field winding into several sections
(c) either of (a) or (b) above
(d) none of the above

36. In steam power plant which of the following component needs more maintenance:
(a) Condenser
(b) Boiler
(c) Turbine
(d) Coal carrying system

37. For the flue gas flow, tick the correct sequence:
(a) Boiler-Air preheater- economizer- ID fan- Chimney
(b) Boiler- ID fan -Air preheater- Economizer- Chimney
(c) Boiler- Economizer- Air preheater- ID fan- Chimney
(d) None of these

38. Hydrogen cooling employed in large thermal power plant alternator:
(a) Increases the insulation life
(b) Decreases the insulation life
(c) Does not effect the insulation life
(d) None of these

39. Economizer is normally employed when boiler pressure exceeds:
(a) 70 kg/cm2
(b) 50 kg/cm2
(c) 30 kg/cm2
(d) can be used for all pressures

40. In thermal power plants the condenser used is of:
(a) surface type
(b) jet type
(c) can be both surface type and jet type
(d) none of these

41. The relation between traveling voltage wave and current wave is
(a) e = i (L/C) ½
(b) e = i (C/L) ½
(c) e = i (iL/C) ½
(d) (L/iC) ½

42. Stability of a system is not affected by
(a) Reactance of line
(b) Losses
(c) Reactance of generator
(d) Output torque.

43. In order to increase the limit of distance of transmission line
(a) series resistances are used
(b) synchronous condensers are used
(c) shunt capacitors and series reactors are used
(d) series capacitors and shunt reactors are used

44. An emitter in a bipolar junction transistor is doped much more heavily than the base as it increases the
(a) Emitter efficiency
(b) Base transport factor
(c) Forward current gain
(d) All of these

45. A zener diode works on the principle of
(a) Tunneling of charge carriers across the junction
(b) Thermionic emission
(c) Diffusion of charge carriers across the junction
(d) Hopping of charge carriers across the junction

46. A long specimen of p-type semiconductor material
(a) is positively charged
(b) is electrically neutral
(c) has an electrical filed directed along its length
(d) acts as a dipole

47. Under small signal operation of a diode
(a) its bulk resistance increases
(b) its junction resistance predominates
(c) it acts like a closed switch
(d) it behaves as a clipper

48. In a multi stage R-C coupled amplifier the coupling capacitor
(a) limits the low frequency response
(b) limits the high frequency response
(c) does not affect the frequency response
(d) block the d.c. component without affecting the frequency response

49. A triangular square wave generator uses
(a) a sine wave oscillation and a comparator
(b) an integrator and a comparator
(c) a differentiator and a comparator
(d) a sine wave oscillator and a clipper

50. The race around condition exists in J-K flip flop if
(a) J=0; K=1
(b) J=1; K=0
(c) J=0; K=0
(d) J=1; K=1