Basic of Electrical Engineering

Application of motor in everyday life.

What are some examples of everyday items that use motors? Fuel motors : 1. Cars and bikes - Diesel and Petrol engines. 2. Water Pump - Diesel engine motor 3. Diesel generator - Petrol,diesel and ...

Norton's Theorem

Norton’s Theorem The Norton’s theorem explains the fact that there are two terminals and they are as follows: • One is terminal active network containing ...

Why humming sound occurred in HT transmission line?
This sound is coming due to ionization (breakdown of air
into charged particles) of air around transmission conductor.
This effect is called as Corona effect, and it is considered as
power loss.

Why humming sound occurred in HT transmission line This sound is coming due to ionization (breakdown of air into charged particles) of air around transmission conductor. This effect is ca...

1. In an open loop control system
(a) Output is independent of control input
(b) Output is dependent on control input
(c) Only system parameters have effect on the control output
(d) None of the above
Ans: a
2. For open control system which of the following statements
is incorrect ?
(a) Less expensive
(b) Recalibration is not required for maintaining the required
quality of the output
(c) Construction is simple and maintenance easy
(d) Errors are caused by disturbances
Ans: b
3. A control system in which the control action is somehow
dependent on the output is known as
(a) Closed loop system
(b) Semiclosed loop system
(c) Open system
(d) None of the above
Ans: a
4. In closed loop control system, with positive value of
feedback gain the overall gain of the system will
(a) decrease
(b) increase
(c) be unaffected
(d) any of the above
Ans: a
5. Which of the following is an open loop control system ?
(a) Field controlled D.C. motor
(b) Ward leonard control
(c) Metadyne
(d) Stroboscope
Ans: a
6. Which of the following statements is not necessarily correct
for open control system ?
(a) Input command is the sole factor responsible for providing
the control action
(b) Presence of non-linearities causes malfunctioning
(c) Less expensive
(d) Generally free from problems of non-linearities
Ans: b
7. In open loop system
(a) the control action depends on the size of the system
(b) the control action depends on system variables
(c) the control action depends on the input signal
(d) the control action is independent of the output
Ans: d
8 has tendency to oscillate.
(a) Open loop system
(b) Closed loop system
(c) Both (a) and (b)
(d) Neither (a) nor (b)
Ans: b
9. A good control system has all the following features except
(a) good stability
(b) slow response
(c) good accuracy
(d) sufficient power handling capacity
Ans: b
10. A car is rtyining at a constant speed of 50 km/h, which of
the following is the feedback element for the driver ?
(a) Clutch
(b) Eyes
(c) Needle of the speedometer
(d) Steering wheel
(e) None of the above
Ans: c
11. The initial response when tne output is not equal to input
is called
(a) Transient response
(b) Error response
(c) Dynamic response
(d) Either of the above
Ans: a
12. A control system working under unknown random actions
is called
(a) computer control system
(b) digital data system
(c) stochastic control system
(d) adaptive control system
Ans: c
13. An automatic toaster is a ______ loop control system.
(a) open
(b) closed
(c) partially closed
(d) any of the above
Ans: a
14. Any externally introduced signal affecting the controlled
output is called a
(a) feedback
(b) stimulus
(c) signal
(d) gain control
Ans: b
15. A closed loop system is distinguished from open loop
system by which of the following ?
(a) Servomechanism
(b) Feedback
(c) Output pattern
(d) Input pattern
Ans: b
16 is a part of the human temperature control system.
(a) Digestive system
(b) Perspiration system
(c) Ear
(d) Leg movement
Ans: b
17. By which of the following the control action is determined
when a man walks along a path ?
(a) Brain
(b) Hands
(c) Legs
(d) Eyes
Ans: d
18 is a closed loop system.
(a) Auto-pilot for an aircraft
(6) Direct current generator
(c) Car starter
(d) Electric switch
Ans: a
19. Which of the following devices are commonly used as
error detectors in instruments ?
(a) Vernistats
(b) Microsyns
(c) Resolvers
(d) Any of the above
Ans: d
20. Which of the following should be done to make an
unstable system stable ?
(a) The gain of the system should be decreased
(b) The gain of the system should be increased
(c) The number of poles to the loop transfer function should
be increased
(d) The number of zeros to the loop transfer function should
be increased
Ans: b
21 increases the steady state accuracy.
(a) Integrator
(b) Differentiator
(c) Phase lead compensator
(d) Phase lag compensator
Ans: a
22. A.C. servomotor resembles
(a) two phase induction motor
(b) Three phase induction motor
(c) direct current series motor
(d) universal motor
Ans: a
23. As a result of introduction of negative feedback which of
the following will not decrease ?
(a) Band width
(b) Overall gain
(c) Distortion
(d) Instability
Ans: a
24. Regenerative feedback implies feedback with
(a) oscillations
(b) step input
(c) negative sign
(d) positive sign
Ans: d
25. The output of a feedback control system must be a
function of
(a) reference and output
(b) reference and input
(e) input and feedback signal
(d) output and feedback signal
Ans: a
26 is an open loop control system.
(a) Ward Leonard control
(b) Field controlled D.C. motor
(c) Stroboscope
(d) Metadyne
Ans: b
27. A control system with excessive noise, is likely to suffer
from
(a) saturation in amplifying stages
(b) loss of gain
(c) vibrations
(d) oscillations
Ans: a
28. Zero initial condition for a system means
(a) input reference signal is zero
(b) zero stored energy
(c) ne initial movement of moving parts
(d) system is at rest and no energy is stored in any of its
components
Ans: d
29. Transfer function of a system is used to calculate which of
the following ?
(a) The order of the system
(b) The time constant
(c) The output for any given input
(d) The steady state gain
Ans: c
30. The band width, in a feedback amplifier.
(a) remains unaffected
(b) decreases by the same amount as the gain increase
(c) increases by the sane saaaajajt as the gain decrease
(d) decreases by the same amount as the gain decrease
Ans: c
31. On which of the following factors does the sensitivity of a
closed loop system to gain changes and load disturbances
depend ?
(a) Frequency
(b) Loop gain
(c) Forward gain
(d) All of the above
Ans: d
32. The transient response, with feedback system,
(a) rises slowly
(b) rises quickly
(c) decays slowly
(d) decays quickly
Ans: d
33. The second derivative input signals modify which of the
following ?
(a) The time constant of the system
(b) Damping of the system
(c) The gain of the system
(d) The time constant and suppress the oscillations
(e) None of the above
Ans: d
34. Which of the following statements is correct for any closed
loop system ?
(a) All the co-efficients can have zero value
(6) All the co-efficients are always non-zero
(c) Only one of the static error co-efficients has a finite non-
zero value
(d) None of the above
Ans: c
35. Which of the following statements is correct for a system
with gain margin close to unity or a phase margin close to
zero ?
(a) The system is relatively stable
(b) The system is highly stable
(c) The system is highly oscillatory
(d) None of the above
Ans: c
36. Due to which of the following reasons excessive bond
width in control systems should be avoided ?
(a) It leads to slow speed of response
(b) It leads to low relative stability
(c) Noise is proportional to band width
(d) None of the above
Ans: c
37. In a stable control system backlash can cause which of the
following ?
(a) Underdamping
(b) Overdamping
(c) Poor stability at reduced values of open loop gain
(d) Low-level oscillations
Ans: d
38. In an automatic control system which of the following
elements is not used ?
(a) Error detector
(b) Final control element
(c) Sensor
(d) Oscillator
Ans: d
39. In a control system the output of the controller is given to
(a) final control element
(b) amplifier
(c) comparator
(d) sensor
(e) none of the above
Ans: a
40. A controller, essentially, is a
(a) sensor
(b) clipper
(c) comparator
(d) amplifier
Ans: c
41. Which of the following is the input to a controller ?
(a) Servo signal
(b) Desired variable value
(c) Error signal
(d) Sensed signal
Ans:
42. The on-off controller is a _____ system.
(a) digital
(b) linear
(c) non-linear
(d) discontinuous
Ans:
43. The capacitance, in force-current analogy, is analogous to
(a) momentum
(b) velocity
(c) displacement
(d) mass
Ans: d
44. The temperature, under thermal and electrical system
analogy, is considered analogous to
(a) voltage
(b) current
(c) capacitance
(d) charge
(e) none of the above
Ans: a
45. In electrical-pneumatic system analogy the current is
considered analogous to
(a) velocity
(b) pressure
(c) air flow
(d) air flow rate
Ans: d
46. In liquid level and electrical system analogy, voltage is
considered analogous to
(a) head
(b) liquid flow
(c) liquid flow rate
(d) none of the above
Ans: a
47. The viscous friction co-efficient, in force-voltage analogy,
is analogous to
(a) charge
(b) resistance
(c) reciprocal of inductance
(d) reciprocal of conductance
(e) none of the above
Ans: b
48. In force-voltage analogy, velocity is analogous to
(a) current
(b) charge
(c) inductance
(d) capacitance
Ans: a
49. In thermal-electrical analogy charge is considered
analogous to
(a) heat flow
(b) reciprocal of heat flow
(c) reciprocal of temperature
(d) temperature
(e) none of the above
Ans: d
50. Mass, in force-voltage analogy, is analogous to
(a) charge
(b) current
(c) inductance
(d) resistance
Ans: c
51. The transient response of a system is mainly due to
(a) inertia forces
(b) internal forces
(c) stored energy
(d) friction
Ans: c
52 signal will become zero when the feedback signal and
reference signs are equal.
(a) Input
(b) Actuating
(c) Feedback
(d) Reference
Ans: b
53. A signal other than the reference input that tends to affect
the value of controlled variable is known as
(a) disturbance
(b) command
(c) control element
(d) reference input
Ans: a
54. The transfer function is applicable to which of the
following ?
(a) Linear and time-in variant systems
(b) Linear and time-variant systems
(c) Linear systems
(d) Non-linear systems
(e) None of the above
Ans: a
55. From which of the following transfer function can be
obtained ?
(a) Signal flow graph
(b) Analogous table
(c) Output-input ratio
(d) Standard block system
(e) None of the above
Ans: a
56 is the reference input minus the primary feedback.
(a) Manipulated variable
(b) Zero sequence
(c) Actuating signal
(d) Primary feedback
Ans: c
57. The term backlash is associated with
(a) servomotors
(b) induction relays
(c) gear trains
(d) any of the above
Ans:
58. With feedback _____ increases.
(a) system stability
(b) sensitivity
(c) gain
(d) effects of disturbing signals
Ans: a
59. By which of the following the system response can be
tested better ?
(a) Ramp input signal
(b) Sinusoidal input signal
(c) Unit impulse input signal
(d) Exponentially decaying signal
Ans: c
60. In a system zero initial condition means that
(a) The system is at rest and no energy is stored in any of its
components
(b) The system is working with zero stored energy
(c) The system is working with zero reference signal
Ans: a
61. In a system low friction co-efficient facilitates
(a) reduced velocity lag error
(b) increased velocity lag error
(c) increased speed of response
(d) reduced time constant of the system
Ans: a
62. Hydraulic torque transmission system is analog of
(a) amplidyne set
(b) resistance-capacitance parallel circuit
(c) motor-generator set
(d) any of the above
Ans:
63. Spring constant in force-voltage analogy is analogous to
(a) capacitance
(b) reciprocal of capacitance
(c) current
(d) resistance
Ans: b
64. The frequency and time domain are related through which
of the following?
(a) Laplace Transform and Fourier Integral
(b) Laplace Transform
(c) Fourier Integral
(d) Either (b) or (c)
Ans: a
65. An increase in gain, in most systems, leads to
(a) smaller damping ratio
(b) larger damping ratio
(c) constant damping ratio
(d) none of the above
Ans: a
66. Static error co-efficients are used as a measure of the
effectiveness of closed loop systems for specified ________
input signal.
(a) acceleration
(b) velocity
(c) position
(d) all of the above
Ans: d
67. A conditionally stable system exhibits poor stability at
(a) low frequencies
(b) reduced values of open loop gain
(c) increased values of open loop gain
(d) none of the above
Ans: b
68. The type 0 system has ______ at the origin.
(a) no pole
(b) net pole
(c) simple pole
(d) two poles
(e) none of the above
Ans: a
69. The type 1 system has ______ at the origin.
(a) no pole
(b) net pole
(c) simple pole
(d) two poles
Ans: c
70. The type 2 system has at the origin.
(a) no net pole
(b) net pole
(c) simple pole
(d) two poles
Ans: d
71. The position and velocity errors of a type-2 system are
(a) constant, constant
(b) constant, infinity
(c) zero, constant
(d) zero, zero
Ans: c
72. Velocity error constant of a system is measured when the
input to the system is unit _______ function.
(a) parabolic
(b) ramp
(c) impulse
(d) step
Ans: b
73. In case of type-1 system steady state acceleration is
(a) unity
(b) infinity
(c) zero
(d) 10
Ans: b
74. If a step function is applied to the input of a system and
the output remains below a certain level for all the time, the
system is
(a) not necessarily stable
(b) stable
(c) unstable
(d) always unstable
(e) any of the above
Ans: a
75. Which of the following is the best method for determining
the stability and transient response ?
(a) Root locus
(b) Bode plot
(c) Nyquist plot
(d) None of the above
Ans: a
76. Phase margin of a system is used to specify which of the
following ?
(a) Frequency response
(b) Absolute stability
(c) Relative stability
(d) Time response
Ans: c
77. Addition of zeros in transfer function causes which of the
following ?
(a) Lead-compensation
(b) Lag-compensation
(c) Lead-lag compensation
(d) None of the above
Ans: b
78. technique is not applicable to nonlinear system ?
(a) Nyquist Criterion
(b) Quasi linearization
(c) Functional analysis
(d) Phase-plane representation
Ans: a
79. In order to increase the damping of a badly underdamped
system which of following compensators may be used ?
(a) Phase-lead
(b) Phase-lag
(c) Both (a) and (b)
(d) Either (a) and (b)
(e) None of the above
Ans: a
80. The phase lag produced by transportation relays
(a) is independent of frequency
(b) is inverseh'proportional to frequency
(c) increases linearly with frequency
(d) decreases linearly with frequency
Ans: c
81. In a stable control system saturation can cause which of
the following ?
(a) Low-level oscillations
(b) High-level oscillations
(c) Conditional stability
(d) Overdamping
Ans: a
82. Which of the following can be measured by the use of a
tacho-generator ?
(a) Acceleration
(b) Speed
(c) Speed and acceleration
(d) Displacement
(e) None of the above
Ans: b
83 is not a final control element.
(a) Control valve
(b) Potentiometer
(c) Electro-pneumatic converter
(d) Servomotor
Ans: b
84. Which of the following is the definition of proportional
band of a controller ?
(a) The range of air output as measured variable varies from
maximum to minimum
(b) The range of measured variables from set value
(c) The range of measured variables through which the air
output chan¬ges from maximum to minimum
(d) Any of the above
(e) None of the above
Ans: c
85. In pneumatic control systems the control valve used as
final control element converts
(a) pressure signal to electric signal
(b) pressure signal to position change
(c) electric signal to pressure signal
(d) position change to pressure signal
(e) none of the above
Ans: b
86. Pressure error can be measured by which of the following ?
(a) Differential bellows and straingauge
(b) Selsyn
(c) Strain gauge
(d) Strain gauge and potentiometer
Ans: a
87. Which of the following devices is used for conversion of
co-ordinates ?
(a) Microsyn
(b) Selsyn
(c) Synchro-resolver
(d) Synchro-transformer
Ans: c
88. The effect of error damping is to
(a) provide larger settling lime
(b) delay the response
(c) reduce steady state error
(d) any of the above
(e) none of the above
Ans: c
89 technique gives quick transient and stability response
(a) Root locus
(b) Bode
(c) Nyquist
(d) Nichols
Ans: a
90. A phase lag lead network introduces in the output
(a) lag at all frequencies
(b) lag at high frequencies and lead at low frequencies
(c) lag at low frequencies and lead at high frequencies
(d) none of the above
Ans: c

State the difference between generator and alternator
Generator and alternator are two devices, which converts
mechanical energy into electrical energy. Both have the same
principle of electromagnetic induction, the only difference is
that their construction. Generator persists stationary magnetic
field and rotating conductor which rolls on the armature with
slip rings and brushes riding against each other, hence it
converts the induced emf into dc current for external load
whereas an alternator has a stationary armature and rotating
magnetic field for high voltages but for low voltage output
rotating armature and stationary magnetic field is used

difference between generator and alternator Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of elect...

Why AC systems are preferred over DC systems?
Due to following reasons, AC systems are preferred over DC
systems:
a. It is easy to maintain and change the voltage of AC
electricity for transmission and distribution.
b. Plant cost for AC transmission (circuit breakers,
transformers etc) is much lower than the equivalent DC
transmission
c. From power stations, AC is produced so it is better to use
AC then DC instead of converting it.
d. When a large fault occurs in a network, it is easier to
interrupt in an AC system, as the sine wave current will
naturally tend to zero at some point making the current easier
to interrupt.

Why AC systems are preferred over DC systems? Due to following reasons, AC systems are preferred over DC systems: a. It is easy to maintain and change the voltage of AC electricity ...

Why back emf used for a dc motor? highlight its significance?
The induced emf developed when the rotating conductors of
the armature between the poles of magnet, in a DC motor,
cut the magnetic flux, opposes the current flowing through
the conductor, when the armature rotates, is called back
emf. Its value depends upon the speed of rotation of the
armature conductors. In starting, the value of back emf is
zero.

Why back emf used for a dc motor? highlight its significance? The induced emf developed when the rotating conductors of the armature between the poles of magnet, in a DC motor, cut the magnetic flux...

What is the role of air gap in any electrical machine how does
it affects induce emf ??
The main source of low power factor at which induction motor
operates is the air gap between the stator and the rotor . This
air gap increases the reluctance between the stator and the
rotor , which enhances the magnetizing current for production
of the given mutual flux between the stator and the rotor for a
given supply voltage . Therefore, the no -load current of an
induction motor becomes 30 to 40 per cent of full -load
current , which is remarkably larger than the no -load current
of a transformer for a given kVA rating. The air gap in an
induction motor should be made small so that the induction
motor gives better performance . The small air gap may result
mechanical problems in addition to the noise and losses at
the slot tooth faces.

What is the role of air gap in any electrical machine how does it affects induce emf The main source of low power factor at which induction motor operates is the air gap between the stator and the rotor . This air gap inc...

The typical value of SCR for modern
alternator is
1.5.
0.5.
1.0.
1.2.
Hints
Always the typical value of SCR for modern
alternator is 0.5.

Disadvantages of Harmonics :
Harmonics degrades the performance of power system . Some
of the disadvantages of harmonics in the power distributed
network are listed below :
The harmonics flowing in the distribution network downgrade
the quality of the electrical power supply . There can have
several negative effects on the operation of the power system
Increased losses on the distribution system due to increase in
the effective rms current
Over -load in neutral conductors due to cumulative increase in
the third harmonics created by the single phase loads
Overloads, vibration and premature ageing of the generators ,
transformers and motors as well as increase in the noise level
Overloads and premature ageing of the power factor
correction capacitors
Distortion of the supply voltage that can disturb the operation
of the sensitive loads
Disturbances in the communication networks and telephone
lines
Resonance between the supply inductance and capacitance of
the power factor correction capacitors

Disadvantages of Harmonics Harmonics degrades the performance of power system . Some of the disadvantages of harmonics in the power distributed network are listed b...

What is the power ratio between power in
Star and Delta circuit?
Power is irrespective of connections whether it is star or
delta , power is same in both connection and the ratio of
power is 1 : 1