## Posted by R.Anirudhan

EC2201  ELECTRICAL ENGINEERING
TWO MARK QUESTION AND ANSWERS

UNIT-1
DC machines
1. What is prime mover?
The  basic source  of mechanical  power  which  drives  the  armature  of
the generator is called prime mover.
What are the essential parts of a d.c generator?
1.  Magnetic  frame  or  yoke  2.  Poles  3.  Armature 4.  Commutator,  pole shoes,
armature windings, interpoles 5. Brushes, bearings and shaft.
2. Give the materials used in machine manufacturing?
There  are three  main  materials  used  in m/c  manufacturing they are steel  to
conduct magnetic flux copper to conduct electric current insulation.
3. What are factors on which hysteresis loss?
It depends on magnetic flux density, frequency & volume of the material.
4. What is core loss? What is its significance in electric machines?
When a  magnetic  material  undergoes cyclic magnetization, two  kinds  of
power  losses occur on  it.  Hysteresis and eddy current losses are  called as
core loss. It is important  in  determining heating,  temperature  rise,  rating  &
efficiency  of  transformers, machines & other A.C run magnetic devices.
5. What is eddy current loss?
When  a magnetic  core  carries  a time  varying  flux,  voltages  are induced in  all
possible  path  enclosing  flux.  Resulting  is the  production of  circulating flux in
core. These circulating current do no useful work are known as eddy current and
have power loss known as eddy current loss.
6. How hysteresis and eddy current losses are minimized?
Hysteresis loss can be minimized by selecting materials for core such as silicon
steel & steel alloys with low hysteresis co-efficient and electrical resistivity. Eddy
current losses are minimized by laminating the core.
7. How will you find the direction of emf using Fleming‟s right hand rule?
The  thumb,  forefinger  &  middle  finger  of  right hand  are  held  so  that
these fingers are mutually perpendicular to each other, then forefinger gives the
direction of the lines of flux, thumb gives the direction of the relative motion of
conductor and  middle finger gives the direction of the emf induced.
8.  How  will  you  find the  direction  of force  produced  using  Fleming‟s left  hand
rule?
The  thumb,  forefinger  &  middle  finger of  left  hand  are  held  so  that these
fingers  are  mutually  perpendicular to  each  other,  then forefinger gives the
direction of magnetic  field, middle finger gives the direction of the current and
thumb gives the direction of the force experienced by the conductor.
9. What is the purpose of yoke in d.c machine?
1. It  acts  as  a  protecting cover  for  the  whole machine and  provides
mechanical support for the poles.
2. It carries magnetic flux produced by the poles
10. What are the types of armature winding?
1. Lap winding, A=P,
2. Wave winding, A=2.
11. How are armature windings are classified based on placement of coil inside
the armature slots?
Single and double layer winding.
12. Write down the emf equation for d.c.generator?
E=(ФNZ/60)(P/A)V.
p---------no of poles
Z---------Total no of conductor
Ф---------flux per pole
N---------speed in rpm.
13.  Why the  armature  core  in  d.c machines  is  constructed  with  laminated
steel  sheets
instead of solid steel sheets?
Lamination highly reduces the  eddy  current  loss  and  steel  sheets provide low
reluctance path to magnetic field.
14. Why commutator is employed in d.c.machines?
Conduct electricity between  rotating armature and  fixed  brushes,  convert
alternating emf into unidirectional emf(mechanical rectifier).
15. Distinguish between shunt and series field coil construction?
Shunt  field  coils  are wound  with  wires  of  small  section  and  have  more no  of
turns. Series field  coils are wound with wires  of larger  cross section  and  have
less no of turns.
16. How does d.c. motor differ from d.c. generator in construction?
Generators  are  normally  placed  in  closed  room  and  accessed  by  skilled
operators  only.  Therefore  on  ventilation  point of  view they may  be
constructed  with  large opening in the frame. Motors have to be installed right
in  the  place  of  use which  may  have  dust,  dampness,  inflammable  gases,
chemical etc. to protect  the  motors  against  these elements the motor frames
are used partially closed or totally closed or flame proof.
17. How will you change the direction of rotation of d.c.motor?
Either the field direction or direction of current  through  armature conductor is
reversed.
18. What is back emf in d.c. motor?
As the motor armature  rotates, the system of conductor come across alternate
north and south pole magnetic fields causing an emf induced in the conductors.
The direction of the emf induced in the  conductor is in opposite to  current. As
this  emf  always  opposes the  flow of  current  in motor  operation  it is  called  as
back emf.
19. What is the function of no-voltage release coil in d.c. motor starter?
As  long  as  the  supply voltage  is  on  healthy  condition  the  current through
the  NVR  coil produce  enough  magnetic  force of  attraction  and  retain  the
starter handle in ON position against spring force. When the supply voltage fails
or  becomes lower than  a  prescribed  value  then  electromagnet  may  not
have  enough  force  to  retain  so  handle will come back to OFF position due to
spring force automatically.
20. Enumerate the factors on which speed of a d.c.motor depends?
N= (V-IaRa)/Ф so speed depends on voltage applied to armature, flux per pole,
resistance  of  armature.
21. Under what circumstances does a dc shunt generator fails to generate?
Absence  of  residual  flux, initial  flux setup by  field  may  be  opposite  in
direction  to  residual  flux,  shunt  field  circuit  resistance may  be  higher
than  its critical  field  resistance, load  circuit  resistance may  be less than its
critical load resistance.
22. Define critical field resistance of dc shunt generator?
Critical field resistance is defined as the resistance of the field circuit which will
cause the shunt generator just to build up its emf at a specified field.
23.  Why  is  the  emf  not  zero  when the  field current  is  reduced  to zero  in  dc
generator?
Even after the field current is reduced to zero, the machine is left out with some
flux as residue so emf is available due to residual flux.
24. On what occasion dc generator may not have residual flux?
The  generator  may  be  put for its operation  after  its  construction,  in
previous operation, the generator would have been fully demagnetized.
25.  What  are  the  conditions  to  be  fulfilled  by  for  a  dc  shunt  generator
to  build  back emf?
The  generator  should  have  residual  flux,  the field  winding  should  be
connected  in  such  a manner that the  flux  setup  by  field in same  direction  as
residual flux, the field resistance should be less than critical field resistance, load
circuit resistance should be above critical resistance.
26. Define armature reaction in dc machines?
The  interaction between  the  main flux  and  armature  flux cause
disturbance called as armature reaction.
27. What are two unwanted effects of armature reactions?
Cross magnetizing effect & demagnetizing effect.
28. What is the function of carbon brush used in dc generators?
The  function  of  the  carbon brush is  to  collect current from commutator
and supply to external load circuit and to load.
29. What is the principle of generator?
When  the armature conductor  cuts the magnetic flux  emf is  induced  in  the
conductor.
30. What is the principle of motor?
When a current carrying conductor is placed in a magnetic field it experiences a
force tending to move it.
31. What are different methods of speed control in D.C shunt motor?
1. Armature control
2. Flux or field control
3. Applied voltage control
32. When is a four point DC starter required in DC motors?
A four point DC starter is required for dc motor under field control
33.  If  speed  is  decreased  in a  dc  motor,  what  happens to  the  back emf
decreases and armature current?
If  speed  is  decreased  in  a  dc  motor,  the  back emf  decreases and  armature
current increases.
34. How does a series motor develop high starting torque?
A  dc  series  motor  is  always  started  with  some load.  Therefore  the  motor
armature  current increases.  Due  to  this, series  motor  develops  high  starting
torque.
35. What is the necessity of starter in dc motors?
When a dc motor is directly switched on, at the time of starting, the motor back
emf is zero. Due to this, the armature current is very high. Due to the very high
current, the motor gets damaged. To reduce the starting current of the motor a
starter is used.
36. Mention the types of braking of dc motor?
1. Regenerative braking
2. Dynamic braking
3. Plugging
37. What are the losses in dc motor?
1. Copper losses
2. Iron losses
3. Mechanical losses
38. Name any 2 non-loading method of testing dc machines?
1. Swinburne‟s test
2. Hopkinson test

UNIT-2
Induction motors

39. Define a transformer?
A transformer is a static device which changes the alternating voltage from one
level to another.
40. What is the turns ratio and transformer ratio of transformer?
Turns ratio = N2/ N1
Transformer = E2/E1 = I1/ I2 =K
41. Mention the difference between core and shell type transformers?
In core type, the windings surround the core considerably and in shell type the
core surrounds the windings i.e winding is placed inside  the core.
42. What is the purpose of laminating the core in a transformer?
In order to minimise eddy current loss.
43. Give the emf equation of a transformer and define each term?
Emf  induced  in  primary  coil E1=  4.44fФmN1  volt  emf  induced  in
secondary
Coil E2 =4.44 fФmN2.
f--------freq of AC input
Ф-----------maximum value of flux in the core
N1, N2---------Number of primary & secondary turns.
44. Does transformer draw any current when secondary is open? Why?
Yes,  it(primary)  will draw the current  from the main  supply in  order to
magnetize the core and to supply for iron and copper losses on no load. There
will not be any current in the secondary since secondary is open.
45. Define voltage regulation of a transformer?
When  a transformer is  loaded  with a  constant  primary  voltage, the
secondary voltage
decreases  for lagging  PF  load,  and  increases  for  leading  PF load because
of  its  internal  resistance  and leakage  reactance. The  change  in  secondary
terminal voltage from no load to  full load  expressed  as  a  percentage  of  no
load  or  full  load  voltage  is  termed  as regulation.
%regulation down=(V2noload- V2full load)*100/ V2noload,
%regulation up=(V2noload-V2F.L)*100/V2F.L
46. Define all day efficiency of a transformer?
It  is  computed  on  the  basis  of  energy  consumed  during a  certain
period, usually a day of 24 hrs. all day efficiency=output in kWh/input in kWh for
24 hrs.
47. Why transformers are rated in kVA?
Copper loss of a transformer depends on current & iron loss on voltage. Hence
total  losses  depend  on  Volt-Ampere  and  not  on  PF.  That  is  why the rating  of
transformers are in kVA and not in kW.
48. What determines the thickness of the lamination or stampings?
1. Frequency
2. Iron loss
49. What are the typical uses of auto transformer?
1.  To  give  small  boost  to  a distribution cable  to  correct for  the
voltage drop.
2. As induction motor starter.
50. What are the applications of step-up & step-down transformer?
Step-up transformers are used in generating stations.  Normally the generated
voltage will be either 11kV. This voltage (11kV) is stepped up to 110kV or 220kV
or 400kV and transmitted through transmission lines  (simply called as  sending
end voltage).
Step-down transformers are used in receiving stations. The voltage are stepped
down  to 11kV  or  22kV  are  stepped  down  to 3phase  400V  by means  of  a
distribution  transformer  and  made  available  at consumer premises.  The
transformers used at generating stations are called power transformers.
51. How transformers are classified according to their construction?
1. Core type  2.shell type.  In  core type,  the winding (primary  and
secondary)  surround the core and in shell type, the core surround the winding.
52. Explain on the material used for core construction?
The core is constructed by sheet steel laminations assembled to provide a
continuous magnetic path with minimum of air gap included.  The  steel  used  is
of  high  silicon  content sometimes heat treated to produce a high permeability
and  a  low hysteresis  loss at  the  usual  operating  flux  densities.  The  eddy
current  loss is  minimized  by  laminating  the core,  the laminations being
used from each other by light coat of core-plate vanish or by oxide layer on the
surface.  The  thickness of  lamination  varies  from  0.35mm  for a  frequency
of  50Hz  and 0.5mm for a frequency of 25Hz.
53. How does change in frequency affect the operation of a given transformer?
With a change in frequency, iron and copper loss, regulation, efficiency &
heating varies so the operation of transformer is highly affected.
54. What is the angle by which no-load current will lag the ideal applied voltage?
In an ideal transformer, there are no copper & core loss i.e. loss free core.
The  no  load  current  is  only magnetizing current therefore the  no  load  current
lags behind by angle 900. However the winding possess resistance and leakage
reactance and therefore the no load current lags the applied voltage slightly less
than 900.
55. List the arrangement of stepped core arrangement in a transformer?
1. To reduce the space effectively
2. To obtain reduce length of mean turn of the winding
3.  To reduce I^2R loss.
56. Why are breathers used in transformers?
Breathers are used to  entrap the  atmospheric moisture  and thereby not
allowing it to pass on to the transformer oil.  Also  to permit the  oil  inside  the
tank  to  expand  and  contract  as  its temperature increases and decreases.
57. What is the function of transformer oil in a transformer?
1. It provides good insulation
2. Cooling.
58. Can the voltage regulation go –ive? If so under what condition?
Yes, if the load has leading PF.
59. Distinguish power transformers & distribution transformers?
Power transformers have very high rating in the order of MVA. They are used in
generating and  receiving  stations.  Sophisticated  controls  are required.  Voltage
ranges will be very high.  Distribution transformers are used in  receiving  side.
Voltage  levels  will  be  medium.  Power  ranging  will  be  small in  order  of  kVA.
Complicated controls are not needed.
60. Name the factors on which hysteresis loss depends?
1. Frequency 2. Volume of the core 3. Maximum flux density
61. Why the open circuit test on a transformer is conducted at rated voltage?
The open circuit on a transformer is conducted at a rated voltage because core
loss depends upon the voltage. This open circuit test gives only core loss or iron
loss of the transformer.
62. What  is  the  purpose  of providing  Taps in  transformer  and where
these  are provided?
In  order  to  attain  the  required  voltage,  taps  are  provided,  normally  at
high  voltages side(low current).
63.  What  are  the  necessary  tests  to  determine  the  equivalent  circuit  of  the
transformer?
1. Open circuit test
2. Short circuit test
64. Define regulation and efficiency of the transformer?
The regulation of the transformer is defined as the reduction in magnitude of the
terminal voltage due to load, with respect to the no-load terminal voltage.
% regulation = (V2  on no-load- V2 when loaded/ V2  on no-load)x 100
Transformer efficiency ƞ= (output power/input power)x 100

UNIT-3
Transformers

65. What are the 2 types of 3phase induction motor?
Squirrel cage and slip ring induction motor.
66. Write two extra features of slip ring induction motor?
Rotor  has 3-phase  winding. Extra  resistance  can  be  added  in  rotor  circuit for
improving PF with the help of three slip rings.
67. Why an induction motor is called as rotating transformer?
The  rotor receives same  electrical  power  in  exactly  the  same  way as the
secondary  of  a  two  winding  transformer receiving its power  from  primary.
That is why induction motor is called as rotating transformer.
68. Why an induction motor never runs at its synchronous speed?
If the motor runs at sync. speed then there would be no relative speed between
the  two,  hence  no  rotor  emf, so  no  rotor  current,  then  no  rotor  torque  to
maintain rotation.
69.  What are slip rings?
The  slip  rings  are  made  of  copper  alloys and  are  fixed  around  the shaft
insulating  it.  Through  these  slip  rings  and  brushes rotor winding  can  be
connected  to external circuit.
70. What are the advantages of cage motor?
Since  the rotor  have  low resistance,  the  copper loss  is  low  and  efficiency
is very high. On account of simple construction of rotor it is mechanically robust,
initial cost is less, maintenance cost is less, simple starting arrangement.
71.  Give  the  condition  for maximum  torque  for  3phase  induction  motor,
when  it  is
running?
The  rotor  resistance  and  reactance  should  be  same  for  max.torque  i.e.
R2=Sx2
72. List out the method for speed control of 3phase cage type induction motor?
By changing supply frequency
By changing no of poles
By operating the two motors in cascade
73. Name the two winding of single phase induction motor?
Running and starting winding.
74. What are methods available for making single phase induction motor a self
starting?
By slitting the single phase, by providing shading coil in the poles.
75. What is the function of capacitor in single phase induction motor?
To make phase difference  between  starting  and  running  winding, to improve
PF and to get more torque.
76. State any 4 use of single phase induction motor?
Fans, wet grinders, vacuum cleaner, small pumps, compressors, drills.
77. What kind of motors used in ceiling fan and wet grinders?
Ceiling fan - Capacitor start and capacitor run single phase induction motor,
wet  grinders -  Capacitor  start  capacitor  run  single  phase  induction  motor.
78. What is the application of shaded pole induction motor?
Because  of  its small  starting  torque,  it  is  generally used  for small  toys,
instruments,  hair driers, ventilators.etc.
79. In which direction a shaded pole motor runs?
The rotor starts rotation in the direction from unshaded part to the shaded part.
80. Why single phase induction motors have low PF?
The  current  through  the  running  winding  lags  behind  the  supply voltage by
large angle so only single phase induction motor have low PF.
81.  Differentiate between  “capacitor  start”  &  “Capacitor  start  capacitor  run”
single Phase induction motor (IM)?
Capacitor start – capacitor  run is connected series with starting winding, but it
will  be  disconnected from  supply when motor  pick  up  its  speed.  Capacitor
start capacitor run- starting  winding  and  capacitor  will not be  disconnected
from  supply  even  though  motor pickup its speed.
82. Explain why  single  phase  induction motor  is  not  a  self  starting  one?
When  motor  fed  supply  from single  phase,  its stator  winding  produces  an
alternating  flux,  which  doesn‟t  develops  any torque.
83. Define slip in an IM?
The slip of an IM is defined as the ratio of difference between sync. speed (Ns)
and rotor speed (N) to the sync. speed.
s= (Ns – N)/ Ns
84. Define slip speed in an IM?
The  slip  speed  is  defined  as the  difference  in  speed  between  the rotating
magnetic field produced by stator (Ns) and rotor speed (N).
85. What is the speed of the rotor field in space?
The speed of the rotor field in space is speed of rotating field.
86. What is sync. speed in 3-phase IM?
Ns = 120f/p
Where f- supply frequency
P- No of poles on the stator.
87. List the various methods of speed control of 3 phase IM?
Types of stator side control
1. Stator voltage control
2. Stator frequency control
3. v/f control
4. pole changing method
88.  In which  type of  motor  can  resistance  be  introduced in the  rotor circuit?
What is the effect of it?
Slip ring IM.
Effects:
1. starting torque increased
2. starting current decreased
3. motor speed can be controlled
89. Why the slots on the IM are usually skewed?
In order to obtain a uniform torque,  reduce the magnetic locking of the  stator
and rotor  and reduce the magnetic humming noise while running.
90. What are the types of poly phase IM?
1. Squirrel cage IM
2. Slip ring IM
91. What  will  be the effect  when  stator  voltage  and freq  of  a  IM  are  reduced
proportionally?
1. Motor speed increases
2. Maximum torque is constant
92. What is slip power recovery scheme?
Slip power can be  returned to the supply source and can be used to supply an
additionalmotor  which  is mechanically  coupled to the main  rotor.  This type  of
drive is known as slip power recovery system and improves overall efficiency of
the system.

UNIT-4
Synchronous and Special electrical machines

93. What are the principal advantages of rotating field type construction?
Relatively  small  amount  of power required for  field system  can  easily
supplied  to rotating system using slip rings and brushes, more space is available
in the stator part of the machine to provide more insulation, it is easy to provide
cooling system, stationary system of conductors can easily be braced to prevent
deformation.
94.  What are  the  advantages  of  salient  type  pole  construction used  in
sync.machines?
They allow better ventilation, the pole faces are so shaped radial air gap length
increases from pole center to pole tips so flux distortion in air gap is sinusoidal
so emf is also sinusoidal.
95. Which type of sync. generators are used in hydroelectric plants and why?
As  the  speed  of  operation is  low,  for hydro  turbines used  in  hydroelectric
plants,  salient  pole  type  sync. generator  is  used  because it  allows better
ventilation  also  better than smooth cylindrical type rotor
96. Why are alternators rated in KVA and not in KW?
As  load increases  I2R  loss also  increases,  as the  current  is  directly
related  to apparent  power  delivered  by generator,  the  alternator has  only
their  apparent  power  in VA/KVA/MVA as their power rating.
97. Why the  sync. impedance  method  of  estimating  voltage  regulation  is  is
considered  as pessimistic method?
Compared to  other  method,  the  value  of  voltage regulation obtained  by  this
method  is always  higher  than the  actual  value  so  it  is  called  as  pessimistic
method.
98.  Why   MMF  method  of  estimating voltage  regulation  is  considered  as
optimistic method?
Compared to  EMF  method,  MMF  method  involves  more no. of  complex
calculation steps.  Further the  OCC  is  referred  twice  and  SCC  is  referred  once
while predetermining the voltage regulation for each load condition. Reference of
OCC takes core saturation effect. As
this method require more effort, final result is very close to actual value, hence
this method is called as optimistic method.
99. Define voltage regulation of the alternator?
It  is  defined  as  the increase  in  terminal  voltage  when full  load  is  thrown  off,
assuming field current and speed remaining the same.
% reg = [(E0 – V)/V]x100
Where E0 = no terminal voltage           V = full load rated terminal voltage
100.  How is  arm.  winding  in alternators  is  different  from those  used  in  dc
machines?
The arm. winding of the alternator is placed in the stator, but in the case of dc
machines the arm winding is placed in the rotor.
101. What is hunting how can it be prevented?
When  a  sync  motor is  used  for driving a  fluctuating  load, the  rotor  starts
oscillating about its new position of equilibrium corresponding to the new load.
This is  called hunting or phase  swinging. To prevent hunting dampers are
damping grids are employed.
102 what are different torques of a sync motor?
1. Starting torque
2. Running torque
3. Pull-in torque
4. Pull-out torque
103. define step angle?
It is  defined  as  angle through which the stepper motor  shaft  rotates  for each
command pulse. It is denoted as β, i)β=[(Ns-Nr)/ Ns.Nr]x360o
Where Ns = no. of stator poles or stator teeth
Nr = no. of rotor poles or rotor teeth
ii) β = 3600/mNr
Where m= no. of stator poles
104. What are different types of stepper motor?
1. Variable reluctance (VR) motor
2. Permanent magnet (PM) stepper motor
3. Hybrid stepper motor
105. What is the advantage in using stepper motor?
1. it can drive open loop without feedback
2. it requires little or no maintenance.
106. Give the applications of stepper motor?
1. Robotics
2. Computer peripherals
3. Facsimile machine
4. Aerospace
107. What are the adv. of reluctance m/c?
1. Motor speed  is constant
2. Simple construction

UNIT- 5
Transmissions and Distribution

108. What are the principle divisions of an electric motor?
1. Generating station
2. Transmission systems
3. Distribution systems
109. List out the types of power generating systems?
1. Steam thermal power station
2. Nuclear power station
3. Hydro electric power station
4. Diesel power station
110. What is the adv. of EHVDC system?
1. Requires less space compared to ac for same voltage rating and size
3. cheaper for long distance transmission.
4. There is no inductance, capacitance, phase displacement and surge problems.
5. There is no skin effect. Therefore entire cross section of the conductor is used.
111. What are the desirable properties of insulators?
1. High mechanical strength to withstand conductor load
2. High electrical strength to prevent leakage current.
3. It should not have any pores in air spaces.
112. List out the types of overhead line insulators?
1. Pin type
2. Suspension type
3. Strain type
4. Shackle
113. What are the adv and dis adv of under ground cables?
Adv:
1. Low vtg drop
2. Low faults
3. Good appearance
4. Less damage through lightening and storms.
Dis adv:
1. High installation cost
2. Insulation problems at high voltage
114. How cables are classified according to the voltage?
Low tension cable – upto 1000V
High tension cable – upto 11kV
Super tension cable – from 22kV to 33kV
Extra high tension cable – from 33kV to 66kV
Extra super tension cable – above 132kV
115. What is the voltage level of sub-transmission system?
33kV or 66kV
116. What are the major electrical equipments used in the power system?
Generator, power transformer, bus bars, circuit breakers, switching circuits
117. What is the function of circuit breaker in power system ?
It is one of the protective equipments in substation. The main function of the CB
is to open or close a circuit under normal as well as fault conditions.
118. What is the sub-transmission network?
The primary transmission line goes upto the receiving station. The voltage is
stepped down to 33kV by step-down transformer i.e. 132/33kV. This 33kV is
transmitted by 3-phase, 3-wire, overhead system. It is a secondary
transmission.
119. Name few insulating materials used in cables.
Rubber, vulcanised India rubber, what are the major impregnated paper, PVC,
varnished cambric.
120. what are the major sources of energy used in the power system?
1. Coal
2. Water
3. Nuclear
121. What is the level of voltage for a) generation b) transmission c)distribution
a) 11kV b) 132kV or 440kV c) 440V or 230 V
122. What are the different types of HVDC links?
1. Monopolar link
2. Bipolar link
3. Homopolar link
123. What is meant by distribution system?
The part of power system which distributes electric power for local use is known
as distribution system.
124. What are the parts of distribution system?
1. Feeders
2. Distributors
3. Service mains
125. What are the different types of distributions?
A)AC distribution:
i) primary distribution system ii) secondary distribution system
b) DC distribution
i)2-wire dc system ii) 3-wire dc system
126. Define sub station
There are number of transformers and switching stations built between
generating stations and the ultimate consumers. These are generally known as
substations.
127. What are the classifications of substation based on?
1. Service requirement
2. Physical features
128. Compare EHVAC with EHVDC  systems?
1. Corona loss and radio interference will be more in EHVAC whereas less in
EHVDC
2. EHVAC requires three conductors whereas EHVDC requires only two
conductors
3. Skin effect will occur in EHVAC whereas skin effect is absent in EHVDC
4. Installation cost of EHVAC is less where cost is more in EHVDC
5. It has inductance, capacitance, phase displacement and surge problems
whereas EHVDC does not has these problems.

PART-B

Unit – I
DC machines
1. What is the principle on which d.c.generator works? List out the main parts of
it. Write details about the construction and function main parts of it.
2.  Describe  the  working  principle  of  d.c generator and  d.c  motor  with  neat
diagrams.
3. Write the expression for emf generated in d.c.machine?
4.  Describe  the different  types  of  d.c.generators  and discuss about  its
characteristics?
5.  Draw the  circuit models  of  d.c.  generator  and  write  relationship  among the
currents and voltage.
6. Derive the torque equation of dc motors?
7. Draw the mechanical characteristics of (N-T) of dc shunt and series of motors
8. Why series motors cannot be started without load.
9. Draw the diagram of three point starter and identified the various parts.
10.  Describe  the  brake  test  on  dc  motors to  determine  the  efficiency
characteristics of dc motors.
11. Explain the Swinburne test to predetermine the efficiency of dc machine.

UNIT -2
Transformers
12. What is Transformers? Define step up and step down Transformer?
13. Classify the transformers according to the construction?
14. Describe the construction of single phase Transformer?
15. Discuss about the working principle of transformers.
16. Derive the equation for the emf induced in a transformer?
17. What is an ideal transformer?
18.  Draw  and  explain  the  no  load  vector  diagram of  ideal  transformers  and
practical
transformers.
19. What are the two components of transformers no load current?
20.  Explain  the  behaviour  of  a  transformer  on  load  with  relevant  to phasor
diagrams?
21. Derive the equivalent circuit of single phase two winding transformers?
22.  Explain  the  OC and  SC  test on  single  phase  transformers.  Develop  the
equivalent circuit
from the above tests?
23. Draw the phasor diagram and explain the operation of practical transformer
on load?
24. Define voltage regulation. Draw the phasor diagram for lagging power factor
and determine voltage regulation.

Unit -3
Induction motors
25. Explain the construction details of 3-phase IM and write its advantages.
26. With neat sketches discuss about the two types of 3-phase IM.
27. Derive the torque developed in 3-phase IM
28. Draw and explain the torque-slip characteristics of a 3-phase IM.
29. Draw and explain the power flow diagram of a 3-phase IM.
30. Develop a equivalent circuit for a 3-phase IM.
31. Explain about the different types of starters in a 3-phase IM and discuss
about its operation.
32. Discuss the various methods of speed control in a 3-phase IM.

Unit -4
Synchronous and special electrical machines

33. Derive an expression for the induced emf of an alternator
34. Explain the emf method to determine the voltage regulation of alternators.
35. Define voltage regulation. Name two methods used to determine voltage
regulation of alternators.
36. Explain the construction and working principle of sync motor. Give the
reasons for making two different types of rotors.
37. What are the advantages of having stationary armature winding in 3 phase
synchronous generator? Mention some special features of sync machine.
38. Write short notes on a) reluctance motor b) stepper motor c) hysteresis
motor
39. Explain in detail the different modes of operation of stepper motor. Mention
some applications of stepper motor.
40. Explain the construction, working principle and applications of following
special machines a) reluctance motor b) stepper motor c) hysteresis motor.
41. Explain the principle of operation of permanent magnet stepper motor.

Unit-5
Transmission and Distribution

42. Draw the schematic diagram of an electric power system. Briefly explain the
structure.
43. State the EHV transmission systems with the salient features.
44. Discuss about the types of cables used in power systems.
45. What do you meant by one line diagram in electric power system?
46. Explain in detail various types of insulators and their applications to power
transmission.
47. Write short notes on a) radial distribution system b) insulating materials for
cables c) pole mounted sub-station
48. Where is sub-station located .explain the classifications of the sub-station.?
49. Explain the connection schemes of distribution system.
50. What is the function of circuit breaker in power system?
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