BASIC ELECTRICAL ENGINEERING QUESTIONS AND ANSWERS PART - 1, 51-100 QUESTIONS
51. What are the types of capacitor?
a. Paper capacitor.
b. Rolled plastic cover or polyester type capacitor.
c. Mica capacitor.
d. Silver mica capacitor.
e. Ceramic capacitor.
f. Electrolytic capacitor.
52. What is the resultant capacitance in series and parallel circuit?
In series circuit the resultant capacitance 1/CT = 1/c1+1/c2 + 1cn farad.
In parallel circuit the resultant capacitance CT = c1 + c2 + cn farad.
-
53. What is the formula to find the capacitance in a circuit?
C = Q/E farad.
PKR ELECTRICAL ENGINEERING
54. What is work?
Work is said to be done, when the point of application of the force moves.
Work
done is equal to force * distance.
The unit of work is Newton (M.K.S system) and
joule (1 Newton Meter).
55. What is power?
Power is the rate of doing work or power is the work done per second.
Power = Work / time.
Unit of electrical power is watt.
One mechanical horsepower is equal to 746 watts
(British) and 735.5 watts (metric) or 735.5 joules/sec. So 1 kW is equal to 1.34
horsepower (British) and 1.36 horsepower (metric).
56. What is energy?
Energy is the capacity to do the work. The unit of energy is joule or watt-second or
watt-hour or kilo watt-hour.
57. Define Joule’s law.
The heat generated in conductor (resistance) while the flow of current is directly
proportional to the square of the current, the resistance of the conductor and time for
which the current flows.
H = I2 R t/J calories.
Where J is mechanical equivalent of heat is equal to 4.2 Joules.
In electricity H = 0.24 I2 R t calories.
58. What is electrolysis?
When current passes through an acid or a salt, it de-composes and the two decomposed
portions tend to move in opposite direction. This process is called the
electrolysis.
Or the process of decomposing a liquid by the passage of electric current (DC)
through it is called the electrolysis or electric analysis.
59. What are the Faradays laws of electrolysis?
First law
The mass ions liberated at an electrode are directly proportional to the quantity of
electricity (coulomb Q) which has passed through the electrolyte. That is M∝Q or
M∝I t.
And M = Z I t.
Where Z is electro chemical equivalent.
Second law
If the same quantity of electricity passes through several electrolyte the masses of the
ions liberated are proportional to their respective chemical equivalent.
60. What is electro plating?
The process of depositing a metal on the surface of another metal by electrolysis is
known as electro plating. Usually the plating material will be silver, chromium etc.
61. What are the applications of electrolysis?
a. Electro plating.
b. Purification of copper and extraction of number of metals and number of
commercial compounds like sodium, hydrogen, hydroxide, oxygen etc.
c. Electro typing.
d. Determination of DC polarity.
e. Electro refining of metals.
62. State the laws of magnetism.
a. Magnet imparts its magnetic properties to other metals.
b. When a magnet is suspended freely horizontally, it stands at geographical north
and south.
c. Every magnet has a north and its associated separable South Pole.
d. If a magnet broken in any number of pieces, each piece will act as a separate
magnet having north and south poles.
e. Like poles repulse and unlike poles attracts.
f. The amount of attraction or repulsion is directly proportional to the pole
strength and inversely proportional to the square of the distance between them.
This is some times known as inverse square law.
63. What is flux density?
It is the flux passing per unit area in a substance through a plain at a right angle to
the flux. The letter ‘B’ denotes it and it is measured in Weber/cm2.
B = Q/a Weber/cm2.
64. What is magneto motive force?
The force, which drives the magnetic flux through a magnetic circuit, is called the
magneto motive force.
65. What is permeability?
Permeability of a substance is the conducting power for lines of force of magnetic
material as compared with the air.
66. What is reluctivity?
It is the specific reluctance of a magnetic circuit or magnetic material as in the case
of resistivity in an electric circuit.
67. What is reluctance?
It is the property of a magnetic material, which opposes the establishment of
magnetic flux in it, as in the case resistance in an electric circuit.
68. What is permeance?
It is the reciprocal of reluctance, which helps to develop or establish magnetic flux
easily in a magnetic material as in the case of conductivity in an electrical circuit.
69. What are the methods of magnetization?
a. Tough method
b. By means of electric current
c. Induction method
70. How the polarity of the magnet can be determined?
Polarity of the magnet can be determined by ‘End rule’ and ‘Palm rule’.
71. What are the advantages of electro magnetism?
a. Electro magnets can be magnetised very easily by sending DC through it.
b. Changing the direction of the current through the coil can change the polarity of
the poles.
c. The strength of the magnet can be controlled by the electric current.
d. Electro magnets can be made in any shape depending upon the need.
e. The magnetic strength remains constant as long as the current is constant.
72. State ‘Cork screw rule’ and ‘Right hand thumb rule’.
Cork screw rule
Direction of magnetic lines of force around a straight current carrying conductor can
be determined by these rules.
‘Cork screw rule’ says that, the direction of magnetic lines of force around a straight
current carrying conductor is the same as that in which the cork screw must be
rotated to cause to an advance in the direction of the current in conductor.
Right hand thumb rule
Grasp the conductor with right hand in such a way that the extended thumb must be
in the direction of current in the conductor. Then the folded fingers or encircling
fingers must be in the direction of magnetic lines of force around the conductor.
73. Who discovered electro magnetism?
‘Orsted’ a denish scientist discovered that whenever an electric current passes
through a conductor, a magnetic field will be produced around that conductor in
concentric circle. In addition to that heat will be produced in that conductor.
74. State the faraday’s laws of electro magnetic induction.
In 1831 Faraday discovered the production of electric current in electric conductor
by converting magnetism. Faraday has mentioned two laws known as faraday’s laws
of electro magnetic induction.
First law
Whenever a conductor causes to cut the magnetic lines of force an emf will be
induced in that conductor.
Second law
The quantity of electricity or the value of the emf produced in that conductor is
directly proportional to the rate of change of flux linked with that conductor.
75. How we can find the direction of induced emf?
The direction of induced emf can be find out by the ‘Fleming’s right hand rule’, and
‘lenz’s law’
Fleming’s right hand rule
Fleming’s right hand rule states that, if one extends the thumb, fore finger and
middle finger of the right hand at right angle to each other in such a way that the
thumb point in direction of motion of the conductor, the fore finger in the direction
of flux (from north to south pole), then the middle finger is indicate the direction of
the induced emf in the conductor.
Lenz’s law
The lenz’s law states that, electro magnetically induced current always flows in such
a way or direction that the action of magnetic field set up by induced current tends to
opposes the root cause which produces it.
PKR ELECTRICAL ENGINEERING
76. What is eddy current?
Eddy currents are those which are produced or induced in the mass of metal
whenever the metal are moved in magnetic field of the magnetic field is moved
across the mass metal so as to link it. The direction of this eddy current is always in
opposite direction to the cause to produce them as per lenz’s law.
Eddy current can be calculated by following equation
We = k Bmax2 f2 t2 v watt.
Where k – Constant
Bmax – Maximum flux density
f – frequency of magnetic reversal
t – thickness of each lamination
v – volume if the armature core or mass metal.
Development of eddy current is made use in energy meters to provide controlling
torque and also in form of automatic starters in moving coil measuring instruments.
77. What is magnetic Hysteresis?
Lagging of magnetization or induction flux density ‘B’ behind the magnetising force
‘H’ is known as magnetic hysteresis.
78. What are the types of induced electro motive force?
a. Dynamically induced emf.
b. Statically induced emf.
Statically induced emf can be further divided into two groups.
a. Mutually induced emf.
b. Self induced emf.
79. What are the use of mutual induction and self-induction?
Use of mutual induction
a. Transformers are works on this principle.
b. An inductance furnace makes use of it.
c. Used in ignition coils of motor car, motor cycles, scooters etc.
Use of self-induction
a. In regulators to give reduced voltage to the fans.
b. In fluorescence tube light to give high voltage at the time of starting and to give
law voltage at it’s normal working time.
c. Used in welding plant rectifiers to keep arc stationary by smoothing choke.
80. What are the different methods used to measure the resistance?
The different methods developed to measure the resistances are as follows.
a. Wheat stone bridge.
b. Slide wire bridge.
c. Post office box.
d. Ohm meter.
e. AVO meter or multi meter.
f. Bridge megger.
g. Megger.
81. What is generator? What are the essential parts of the generator?
Generator is a machine, which converts mechanical energy into electrical energy.
A generator works on under the principle of faraday’s laws of electro magnetic
induction.
It’s essential parts are conductor, magnetic field and the movement of either the
conductor or the magnetic field so as to create a rate of change of flux linkage with
the conductor by the action of applied mechanical energy.
82. What is the equation used to find out frequency of number of cycles of induced emf?
f = NP/120
83. What are the types of generators?
There are two types of generator.
a. Permanent magnet generator.
b. Electro magnet generator.
In electro magnet generator there are two types.
a. Self excited generator.
b. Separately excited generator.
84. What are main types of DC generator?
Mainly there are three types.
a. Series generator or series wound generator.
b. Shunt generator or shunt wound generator.
c. Compound generator.
There are different types of compound generator.
a. Short shunt commulative compound generator.
b. Short shunt differential compound generator.
c. Long shunt commulative compound generator.
d. Long shunt differential compound generator.
Depending upon the terminal voltage characteristics there are three types of
compound generator.
a. Under compound generator.
b. Flat or level compound generator.
c. Over compound generator.
85. What is the emf equation for generator?
emf = P * φ * Z * N / A * 60
Where,
φ = Flux per pole in Weber.
Z = Total number of armature conductors.
P = Number of poles.
A = Number of parallel paths in armature.
N = Speed in rpm.
emf = emf generated in one parallel path and it is the emf generated of that generator.
For a wave wound generator there are only two (2) parallel paths in the armature. In
such cases A=2 and in lap wave wound armature parallel paths is equal to the
number of poles in the armature winding.
86. What are the losses in DC generator?
There are two main losses.
a. Copper losses or electrical losses.
b. Stray losses or rotational losses or constant losses.
Copper losses includes following losses
a. Armature copper losses (Ia2 ra).
b. Field copper losses (Ise2 rse) or (Ish2 rsh).
c. Losses in brush.
Stray losses are as follows
a. Magnetic losses (Iron loss or core loss).
b. Mechanical losses.
87. What is efficiency of generator?
Efficiency = Out put / input= Out put / out put + losses
88. What is armature reaction?
Armature reaction is the effect of armature flux on the main field flux.
The effects of armature reaction are follows.
a. Armature reaction destroys (cross magnetizes) and weakens the main field flux
produced by the main pole.
b. It causes to reduce the induced emf in the armature.
c. It causes to reduce the efficiency of machine.
d. It causes to produce sparking at the brushes due to the shifting of M.N.A
(magnetic neutral axis).
e. At short-circuited loads or at very heavy loads, in case of self-excited generators
de-magnetising of pole cores (wiping of residual magnetism) may takes place.
89. What are the remedies for armature reaction?
a. Brushes have to shift to new M.N.A position in the direction of rotation of
armature.
b. To over come the weakening of the field extra turns have to be added in armature.
c. Pole shoes have to modify at trailing pole tip side to increase the reluctance.
d. Pole shoes have to modify to increase the reluctance.
e. In big machines there is chance of load fluctuation, a compensating winding to be
placed at the pole shoes and it is connected in series with the armature winding
such that the current in that winding is opposite to the armature winding.
90. What is commutation?
Usually the width of the brush is equal to the two segments of the commutator.
Whenever a brush contacts two or more commutator segments, the connected to
those segments are short-circuited. After the period of short-circuiting the current on
those coils changes their current direction in it. The change that takes place in the
coil after the period of short-circuiting of that coil is called commutation.
When that changes take place slowly, that commutation is known as smooth
commutation and when that changes take place suddenly, that commutation is known
as rough commutation.
If the commutation is not smooth, the spark may be more and that will damage the
commutator surface, commutator segments and so the winding.
The remedies for rough commutation are resistance commutation method and emf
commutation method.
91. What are the characteristics of DC generator?
There are three main characteristics of DC generator and they are,
a. No load saturation characteristics or OCC or magnetic characteristics (E0/If).
b. Internal or total characteristics (E/Ia).
c. External characteristics (V/I).
92. What is motor? How DC motor works?
A motor is a machine, which takes electrical energy and converts that electrical
energy into mechanical energy.
DC motor works under the principle, that whenever a current carrying conductor
placed in a magnetic field, a mechanical force will be acts upon that conductor and
the conductor tends to rotate, if it is arranged freely to rotate.
The direction of the force or rotation can be determine by “Fleming’s left hand rule”
93. What is torque?
Whenever a current carrying conductor placed in a magnetic field, a mechanical
force will be acts upon that conductor and the conductor tends to rotate, if it is
arranged freely to rotate. This rotation is due to the turning or twisting force acted on
that conductor. This turning or twisting movement of a force about an axis is called
torque ‘T’.
T = force * radius Newton-meter.
Work done per revolution = force * distance covered in one revolution.
∴ Work done per revolution = force * 2πr.
Work done per second = force * 2πr N (r.p.s)
Work done per second = 2π N T (äT = F * r)
So power developed in metric horsepower is equal to force 2πNT/735.5 hp.
94. What are the classifications of DC motor?
a. DC series motor.
b. DC shunt motor.
c. DC compound motor.
There are two types of DC compound motor.
a. Differential compound motor.
b. Commulative compound motor.
95. What are the losses in DC motor?
The losses in DC motor are same as that of DC generator. They are copper losses,
magnetic losses and mechanical losses.
96. What are the characteristics of DC motor?
The characteristics of DC motor shows the relation between armature current (Ia),
speed (N) and torque (T).
a. Torque and armature current characteristics. It is also known as electrical
characteristics.
b. Speed and armature current characteristics.
c. Speed and torque characteristics.
97. What is the necessity of DC motor starter?
Eb = V – Ia ra.
∴ Ia = V – Eb / ra.
At the time of starting from the rest there is no any back emf (Eb) in the armature. So
a large current flows through the armature based on V / ra. This very large current
blow out the fuses and before to that it will damage the commutator, commutator
brushes and winding. To avoid this difficulties a proper resistance has to be
introduce in series with the armature till the motor reaches it’s rated speed or till
development of Eb in the armature to reduce the starting large current to safe value.
This starting resistance is gradually cut out as the motor gains speed and the
develops back emf (Eb) which regulates it’s speed and armature current. This can be
achieved by the help of starter.
98. What are the types of DC motor starter?
a. DC two point starter for series motor.
b. DC three point starter for shunt motor.
c. DC four point starter for compound motor.
99. How speed control of DC motor can be achieved?
Induced emf in the armature E = P * φ * Z * N / A * 60 volts.
Where Z and A are constant.
N ∝ Eb / φ
N ∝ V – Ia ra / φ.
We can consider that the Ia ra drop is very small and there by in the place of V – Ia ra
we can consider only V. If it so then N ∝ V/ φ.
So speed may be varied by varying either applied voltage to the armature and by
varying field flux or field strength per pole or total field flux.
100. What is cell?
Cell is one unit for converting chemical energy into electrical energy. A cell
essentially requires two electrodes, electrolyte and container.
PKR ELECTRICAL ENGINEERING
https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg RRB JE, SSC AE/JE UPSSSC JE, SSC JE, CIVIL ENGINEERING MCQs, ELECTICAL ENGINEERING MCQs, preavious year quesion papers, dmrc, lmrc, drdo,rrb ntpc, ntpc, pgcil, dsssb, states board, GATE IES EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA
a. Paper capacitor.
b. Rolled plastic cover or polyester type capacitor.
c. Mica capacitor.
d. Silver mica capacitor.
e. Ceramic capacitor.
f. Electrolytic capacitor.
52. What is the resultant capacitance in series and parallel circuit?
In series circuit the resultant capacitance 1/CT = 1/c1+1/c2 + 1cn farad.
In parallel circuit the resultant capacitance CT = c1 + c2 + cn farad.
-
53. What is the formula to find the capacitance in a circuit?
C = Q/E farad.
54. What is work?
Work is said to be done, when the point of application of the force moves.
Work
done is equal to force * distance.
The unit of work is Newton (M.K.S system) and
joule (1 Newton Meter).
55. What is power?
Power is the rate of doing work or power is the work done per second.
Power = Work / time.
Unit of electrical power is watt.
One mechanical horsepower is equal to 746 watts
(British) and 735.5 watts (metric) or 735.5 joules/sec. So 1 kW is equal to 1.34
horsepower (British) and 1.36 horsepower (metric).
56. What is energy?
Energy is the capacity to do the work. The unit of energy is joule or watt-second or
watt-hour or kilo watt-hour.
57. Define Joule’s law.
The heat generated in conductor (resistance) while the flow of current is directly
proportional to the square of the current, the resistance of the conductor and time for
which the current flows.
H = I2 R t/J calories.
Where J is mechanical equivalent of heat is equal to 4.2 Joules.
In electricity H = 0.24 I2 R t calories.
58. What is electrolysis?
When current passes through an acid or a salt, it de-composes and the two decomposed
portions tend to move in opposite direction. This process is called the
electrolysis.
Or the process of decomposing a liquid by the passage of electric current (DC)
through it is called the electrolysis or electric analysis.
59. What are the Faradays laws of electrolysis?
First law
The mass ions liberated at an electrode are directly proportional to the quantity of
electricity (coulomb Q) which has passed through the electrolyte. That is M∝Q or
M∝I t.
And M = Z I t.
Where Z is electro chemical equivalent.
Second law
If the same quantity of electricity passes through several electrolyte the masses of the
ions liberated are proportional to their respective chemical equivalent.
60. What is electro plating?
The process of depositing a metal on the surface of another metal by electrolysis is
known as electro plating. Usually the plating material will be silver, chromium etc.
61. What are the applications of electrolysis?
a. Electro plating.
b. Purification of copper and extraction of number of metals and number of
commercial compounds like sodium, hydrogen, hydroxide, oxygen etc.
c. Electro typing.
d. Determination of DC polarity.
e. Electro refining of metals.
62. State the laws of magnetism.
a. Magnet imparts its magnetic properties to other metals.
b. When a magnet is suspended freely horizontally, it stands at geographical north
and south.
c. Every magnet has a north and its associated separable South Pole.
d. If a magnet broken in any number of pieces, each piece will act as a separate
magnet having north and south poles.
e. Like poles repulse and unlike poles attracts.
f. The amount of attraction or repulsion is directly proportional to the pole
strength and inversely proportional to the square of the distance between them.
This is some times known as inverse square law.
63. What is flux density?
It is the flux passing per unit area in a substance through a plain at a right angle to
the flux. The letter ‘B’ denotes it and it is measured in Weber/cm2.
B = Q/a Weber/cm2.
64. What is magneto motive force?
The force, which drives the magnetic flux through a magnetic circuit, is called the
magneto motive force.
65. What is permeability?
Permeability of a substance is the conducting power for lines of force of magnetic
material as compared with the air.
66. What is reluctivity?
It is the specific reluctance of a magnetic circuit or magnetic material as in the case
of resistivity in an electric circuit.
67. What is reluctance?
It is the property of a magnetic material, which opposes the establishment of
magnetic flux in it, as in the case resistance in an electric circuit.
68. What is permeance?
It is the reciprocal of reluctance, which helps to develop or establish magnetic flux
easily in a magnetic material as in the case of conductivity in an electrical circuit.
69. What are the methods of magnetization?
a. Tough method
b. By means of electric current
c. Induction method
70. How the polarity of the magnet can be determined?
Polarity of the magnet can be determined by ‘End rule’ and ‘Palm rule’.
71. What are the advantages of electro magnetism?
a. Electro magnets can be magnetised very easily by sending DC through it.
b. Changing the direction of the current through the coil can change the polarity of
the poles.
c. The strength of the magnet can be controlled by the electric current.
d. Electro magnets can be made in any shape depending upon the need.
e. The magnetic strength remains constant as long as the current is constant.
72. State ‘Cork screw rule’ and ‘Right hand thumb rule’.
Cork screw rule
Direction of magnetic lines of force around a straight current carrying conductor can
be determined by these rules.
‘Cork screw rule’ says that, the direction of magnetic lines of force around a straight
current carrying conductor is the same as that in which the cork screw must be
rotated to cause to an advance in the direction of the current in conductor.
Right hand thumb rule
Grasp the conductor with right hand in such a way that the extended thumb must be
in the direction of current in the conductor. Then the folded fingers or encircling
fingers must be in the direction of magnetic lines of force around the conductor.
73. Who discovered electro magnetism?
‘Orsted’ a denish scientist discovered that whenever an electric current passes
through a conductor, a magnetic field will be produced around that conductor in
concentric circle. In addition to that heat will be produced in that conductor.
74. State the faraday’s laws of electro magnetic induction.
In 1831 Faraday discovered the production of electric current in electric conductor
by converting magnetism. Faraday has mentioned two laws known as faraday’s laws
of electro magnetic induction.
First law
Whenever a conductor causes to cut the magnetic lines of force an emf will be
induced in that conductor.
Second law
The quantity of electricity or the value of the emf produced in that conductor is
directly proportional to the rate of change of flux linked with that conductor.
75. How we can find the direction of induced emf?
The direction of induced emf can be find out by the ‘Fleming’s right hand rule’, and
‘lenz’s law’
Fleming’s right hand rule
Fleming’s right hand rule states that, if one extends the thumb, fore finger and
middle finger of the right hand at right angle to each other in such a way that the
thumb point in direction of motion of the conductor, the fore finger in the direction
of flux (from north to south pole), then the middle finger is indicate the direction of
the induced emf in the conductor.
Lenz’s law
The lenz’s law states that, electro magnetically induced current always flows in such
a way or direction that the action of magnetic field set up by induced current tends to
opposes the root cause which produces it.
76. What is eddy current?
Eddy currents are those which are produced or induced in the mass of metal
whenever the metal are moved in magnetic field of the magnetic field is moved
across the mass metal so as to link it. The direction of this eddy current is always in
opposite direction to the cause to produce them as per lenz’s law.
Eddy current can be calculated by following equation
We = k Bmax2 f2 t2 v watt.
Where k – Constant
Bmax – Maximum flux density
f – frequency of magnetic reversal
t – thickness of each lamination
v – volume if the armature core or mass metal.
Development of eddy current is made use in energy meters to provide controlling
torque and also in form of automatic starters in moving coil measuring instruments.
77. What is magnetic Hysteresis?
Lagging of magnetization or induction flux density ‘B’ behind the magnetising force
‘H’ is known as magnetic hysteresis.
78. What are the types of induced electro motive force?
a. Dynamically induced emf.
b. Statically induced emf.
Statically induced emf can be further divided into two groups.
a. Mutually induced emf.
b. Self induced emf.
79. What are the use of mutual induction and self-induction?
Use of mutual induction
a. Transformers are works on this principle.
b. An inductance furnace makes use of it.
c. Used in ignition coils of motor car, motor cycles, scooters etc.
Use of self-induction
a. In regulators to give reduced voltage to the fans.
b. In fluorescence tube light to give high voltage at the time of starting and to give
law voltage at it’s normal working time.
c. Used in welding plant rectifiers to keep arc stationary by smoothing choke.
80. What are the different methods used to measure the resistance?
The different methods developed to measure the resistances are as follows.
a. Wheat stone bridge.
b. Slide wire bridge.
c. Post office box.
d. Ohm meter.
e. AVO meter or multi meter.
f. Bridge megger.
g. Megger.
81. What is generator? What are the essential parts of the generator?
Generator is a machine, which converts mechanical energy into electrical energy.
A generator works on under the principle of faraday’s laws of electro magnetic
induction.
It’s essential parts are conductor, magnetic field and the movement of either the
conductor or the magnetic field so as to create a rate of change of flux linkage with
the conductor by the action of applied mechanical energy.
82. What is the equation used to find out frequency of number of cycles of induced emf?
f = NP/120
83. What are the types of generators?
There are two types of generator.
a. Permanent magnet generator.
b. Electro magnet generator.
In electro magnet generator there are two types.
a. Self excited generator.
b. Separately excited generator.
84. What are main types of DC generator?
Mainly there are three types.
a. Series generator or series wound generator.
b. Shunt generator or shunt wound generator.
c. Compound generator.
There are different types of compound generator.
a. Short shunt commulative compound generator.
b. Short shunt differential compound generator.
c. Long shunt commulative compound generator.
d. Long shunt differential compound generator.
Depending upon the terminal voltage characteristics there are three types of
compound generator.
a. Under compound generator.
b. Flat or level compound generator.
c. Over compound generator.
85. What is the emf equation for generator?
emf = P * φ * Z * N / A * 60
Where,
φ = Flux per pole in Weber.
Z = Total number of armature conductors.
P = Number of poles.
A = Number of parallel paths in armature.
N = Speed in rpm.
emf = emf generated in one parallel path and it is the emf generated of that generator.
For a wave wound generator there are only two (2) parallel paths in the armature. In
such cases A=2 and in lap wave wound armature parallel paths is equal to the
number of poles in the armature winding.
86. What are the losses in DC generator?
There are two main losses.
a. Copper losses or electrical losses.
b. Stray losses or rotational losses or constant losses.
Copper losses includes following losses
a. Armature copper losses (Ia2 ra).
b. Field copper losses (Ise2 rse) or (Ish2 rsh).
c. Losses in brush.
Stray losses are as follows
a. Magnetic losses (Iron loss or core loss).
b. Mechanical losses.
87. What is efficiency of generator?
Efficiency = Out put / input= Out put / out put + losses
88. What is armature reaction?
Armature reaction is the effect of armature flux on the main field flux.
The effects of armature reaction are follows.
a. Armature reaction destroys (cross magnetizes) and weakens the main field flux
produced by the main pole.
b. It causes to reduce the induced emf in the armature.
c. It causes to reduce the efficiency of machine.
d. It causes to produce sparking at the brushes due to the shifting of M.N.A
(magnetic neutral axis).
e. At short-circuited loads or at very heavy loads, in case of self-excited generators
de-magnetising of pole cores (wiping of residual magnetism) may takes place.
89. What are the remedies for armature reaction?
a. Brushes have to shift to new M.N.A position in the direction of rotation of
armature.
b. To over come the weakening of the field extra turns have to be added in armature.
c. Pole shoes have to modify at trailing pole tip side to increase the reluctance.
d. Pole shoes have to modify to increase the reluctance.
e. In big machines there is chance of load fluctuation, a compensating winding to be
placed at the pole shoes and it is connected in series with the armature winding
such that the current in that winding is opposite to the armature winding.
90. What is commutation?
Usually the width of the brush is equal to the two segments of the commutator.
Whenever a brush contacts two or more commutator segments, the connected to
those segments are short-circuited. After the period of short-circuiting the current on
those coils changes their current direction in it. The change that takes place in the
coil after the period of short-circuiting of that coil is called commutation.
When that changes take place slowly, that commutation is known as smooth
commutation and when that changes take place suddenly, that commutation is known
as rough commutation.
If the commutation is not smooth, the spark may be more and that will damage the
commutator surface, commutator segments and so the winding.
The remedies for rough commutation are resistance commutation method and emf
commutation method.
91. What are the characteristics of DC generator?
There are three main characteristics of DC generator and they are,
a. No load saturation characteristics or OCC or magnetic characteristics (E0/If).
b. Internal or total characteristics (E/Ia).
c. External characteristics (V/I).
92. What is motor? How DC motor works?
A motor is a machine, which takes electrical energy and converts that electrical
energy into mechanical energy.
DC motor works under the principle, that whenever a current carrying conductor
placed in a magnetic field, a mechanical force will be acts upon that conductor and
the conductor tends to rotate, if it is arranged freely to rotate.
The direction of the force or rotation can be determine by “Fleming’s left hand rule”
93. What is torque?
Whenever a current carrying conductor placed in a magnetic field, a mechanical
force will be acts upon that conductor and the conductor tends to rotate, if it is
arranged freely to rotate. This rotation is due to the turning or twisting force acted on
that conductor. This turning or twisting movement of a force about an axis is called
torque ‘T’.
T = force * radius Newton-meter.
Work done per revolution = force * distance covered in one revolution.
∴ Work done per revolution = force * 2πr.
Work done per second = force * 2πr N (r.p.s)
Work done per second = 2π N T (äT = F * r)
So power developed in metric horsepower is equal to force 2πNT/735.5 hp.
94. What are the classifications of DC motor?
a. DC series motor.
b. DC shunt motor.
c. DC compound motor.
There are two types of DC compound motor.
a. Differential compound motor.
b. Commulative compound motor.
95. What are the losses in DC motor?
The losses in DC motor are same as that of DC generator. They are copper losses,
magnetic losses and mechanical losses.
96. What are the characteristics of DC motor?
The characteristics of DC motor shows the relation between armature current (Ia),
speed (N) and torque (T).
a. Torque and armature current characteristics. It is also known as electrical
characteristics.
b. Speed and armature current characteristics.
c. Speed and torque characteristics.
97. What is the necessity of DC motor starter?
Eb = V – Ia ra.
∴ Ia = V – Eb / ra.
At the time of starting from the rest there is no any back emf (Eb) in the armature. So
a large current flows through the armature based on V / ra. This very large current
blow out the fuses and before to that it will damage the commutator, commutator
brushes and winding. To avoid this difficulties a proper resistance has to be
introduce in series with the armature till the motor reaches it’s rated speed or till
development of Eb in the armature to reduce the starting large current to safe value.
This starting resistance is gradually cut out as the motor gains speed and the
develops back emf (Eb) which regulates it’s speed and armature current. This can be
achieved by the help of starter.
98. What are the types of DC motor starter?
a. DC two point starter for series motor.
b. DC three point starter for shunt motor.
c. DC four point starter for compound motor.
99. How speed control of DC motor can be achieved?
Induced emf in the armature E = P * φ * Z * N / A * 60 volts.
Where Z and A are constant.
N ∝ Eb / φ
N ∝ V – Ia ra / φ.
We can consider that the Ia ra drop is very small and there by in the place of V – Ia ra
we can consider only V. If it so then N ∝ V/ φ.
So speed may be varied by varying either applied voltage to the armature and by
varying field flux or field strength per pole or total field flux.
100. What is cell?
Cell is one unit for converting chemical energy into electrical energy. A cell
essentially requires two electrodes, electrolyte and container.
https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg RRB JE, SSC AE/JE UPSSSC JE, SSC JE, CIVIL ENGINEERING MCQs, ELECTICAL ENGINEERING MCQs, preavious year quesion papers, dmrc, lmrc, drdo,rrb ntpc, ntpc, pgcil, dsssb, states board, GATE IES EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA
No comments:
Post a Comment