The document discusses DC machines and induction machines. It provides details on the construction and working of DC generators and motors, including their important parts, methods of excitation, EMF equations, and speed control methods. It also discusses the construction of three-phase induction motors, including squirrel cage and wound rotors. It provides information on synchronous speed, slip, torque-slip characteristics, and compares single phase and three phase induction motors. Starter types for motors like DOL, star-delta, and autotransformer are also explained.

1. UNIT-III
DC MACHINES

2. • MACHINE:
• DC MACHINE:
• DC MOTOR:
• DC GENERATOR:

3. Faradays laws of electromagnetic
induction
• Faradays 1 st law:
When ever conductor cuts magnetic flux an
EMF is induced in that condutor.
• Faradays 2 nd law:
The magnitude of induced emf is equal to the
rate of change of flux linkages.

4. DC MACHINE CONSTRUCTION

5. IMPORTANT PARTS IN DC MACHINE
• A DC generator has the following parts
1) Yoke
2) Pole
3) field winding
4) Armature core
5) Brushes
6) Bearings
7)Commutator
8)Shaft

7. ARMATURE CORE

8. COMMUTATOR

9. BEARINGS & BRUSHES

10. Methods of Excitation
• Separately excitation
• Self excitation
The process of generating a magnetic field by means of an
electric current is called excitation.

11. EMF EQUATION OF
DC GENERATOR

14. CLASSIFICATION OF DC GENERATORS

15. SEPARATELY EXCITED DC GENERATOR

16. SELF EXCITED DC SHUNT GENERATOR

17. SELF EXCITED DC SERIES GENERATOR
Eg=V+IaRa+IseRse

18. SELF EXCITED DC COMPOUND
GENERATOR
SHORT SHUNT COMPOUND LONG SHUNT COMPOUND

22. POWER STAGES IN DC GENERATOR

24. DC MOTORS

26. TORQUE EQUATION IN MOTOR

30. SPEED CONTROL OF DC SHUNT
MOTOR
1.Flux control method
2.Armature resistance control method

31. SPEED CONTROL OF DC SHUNT
MOTOR
FLUX CONTROL METHOD

32. ARMATURE RESISTANCE CONTROL METHOD

33. Power stages in DC motors

34. 3-POINT STARTER

35. TRANSFORMERS

38. Introduction
• A transformer is a static machines.
• The word ‘transformer’comes form the word ‘transform’.
• Transformer is not an energy conversion device, but is a device that
changes AC electrical power at one voltage level into AC electrical
power at another voltage level through the action of magnetic field,
without a change in frequency.
• It can be either to step-up or step down.
Generation
Station
TX1 TX1
Distribution
s TX1
TX1
Transmission System
33/13.5k
V
13.5/6.6kV
6.6kV/415
V
Consumer

39. Transformer Construction
• Two types of iron-core construction:
a) Core - type construction
b) Shell - type construction
• Core - type construction

40. Transformer Construction
• Shell - type construction

41. Ideal Transformer
• An ideal transformer is a transformer which has no loses, i.e.
it’s winding has no ohmic resistance, no magnetic leakage,
and therefore no I2 R and core loses.
• However, it is impossible to realize such a transformer in
practice.
• Yet, the approximate characteristic of ideal transformer will be
used in characterized the practical transformer.
V1 V2
N1 : N2
E1 E2
I1 I2
V1 – Primary Voltage
V2 – Secondary Voltage
E1 – Primary induced Voltage
E2 – secondary induced Voltage
N1:N2 – Transformer ratio

42. Transformer Rating
• Transformer rating is normally written in terms of
Apparent Power.
• Apparent power is actually the product of its rated
current and rated voltage.
2211 IVIVVA 
 Where,
 I1 and I2 = rated current on primary and secondary winding.
 V1 and V2 = rated voltage on primary and secondary winding.
 Rated currents are actually the full load currents in transformer

43. Example
1. 1.5kVA single phase transformer has rated voltage of
144/240 V. Finds its full load current.
Solution
AI
AI
FL
FL
6
240
1500
45.10
144
1500
2
1



44. Practical Transformer (Equivalent Circuit)
V1 = primary supply voltage
V2 = 2nd terminal (load) voltage
E1 = primary winding voltage
E2 = 2nd winding voltage
I1 = primary supply current
I2 = 2nd winding current
I1
’ = primary winding current
Io = no load current
V1
I1 R1
X1
RC
Ic
Xm
Im
Io
E1 E2
V2
I1
’
N1: N2
R2
X2
Load
I2

45. Transformer Losses
• Generally, there are two types of losses;
i. Iron losses :- occur in core parameters
ii. Copper losses :- occur in winding resistance
i. Iron Losses
ii Copper Losses
circuitopenccciron PRIPP  2
)(
02
2
201
2
1
2
2
21
2
1
)()(,
)()(
RIRIPreferredifor
PRIRIPP
cu
circuitshortcucopper



46. Transformer Efficiency
• To check the performance of the device, by
comparing the output with respect to the input.
• The higher the efficiency, the better the system.
%100
cos
cos
%100
%100,
22
22







cuc
lossesout
out
PPIV
IV
PP
P
PowerInput
PowerOutput
Efficiency



%100
cos
cos
%100
cos
cos
2)(
)(






cuc
nload
cuc
loadfull
PnPnVA
nVA
PPVA
VA






Where, if ½ load, hence n = ½ ,
¼ load, n= ¼ ,
90% of full load, n =0.9
Where Pcu = Psc
Pc = Poc

47. Voltage Regulation
• The purpose of voltage regulation is basically
to determine the percentage of voltage drop
between no load and full load.
• Voltage Regulation can be determine based on
3 methods:
a) Basic Defination
b) Short – circuit Test
c) Equivalent Circuit

48. Voltage Regulation
(Basic Definition)
• In this method, all parameter are being referred to
primary or secondary side.
• Can be represented in either
 Down – voltage Regulation
%100. 


NL
FLNL
V
VV
RV
 Up – Voltage Regulation
%100. 


FL
FLNL
V
VV
RV

52. K
I
I
N
N
E
E

2
1
1
2
1
2

57. LOSSES IN TRANSFORMERS
• Copper Loss in Transformer
• Copper loss is I2R loss, in primary side it is I1
2R1 and in secondary side it is I2
2R2
loss, where I1 & I2 are primary & secondary current of transformer and R1 & R2
are resistances of primary & secondary winding. As the both primary &
secondary currents depend upon load of transformer, copper loss in transformer
vary with load.

58. • Core Losses in Transformer
• Hysteresis loss and eddy current loss, both depend upon magnetic properties of the
materials used to construct the core of transformer and its design. So these losses in
transformer are fixed and do not depend upon the load current. So core losses in
transformer which is alternatively known as iron loss in transformer can be
considered as constant for all range of load.
•

61. UNIT-IV
INDUCTION MACHINES

62. Introduction
• Three-phase induction motors are the most common and
frequently encountered machines in industry
– simple design, rugged, low-price, easy maintenance
– wide range of power ratings: fractional horsepower to 10
MW
– run essentially as constant speed from no-load to full load
– Its speed depends on the frequency of the power source
• not easy to have variable speed control
• requires a variable-frequency power-electronic drive
for optimal speed control

63. Construction
• An induction motor has two main parts
STATOR
• consisting of a steel frame that supports a hollow,
cylindrical core
• core, constructed from stacked laminations (why?),
having a number of evenly spaced slots, providing the
space for the stator winding
Stator of IM

64. Construction
ROTOR
• composed of punched laminations, stacked to create a series of rotor
slots, providing space for the rotor winding
• one of two types of rotor windings
• conventional 3-phase windings made of insulated wire (wound-rotor) »
similar to the winding on the stator
• aluminum bus bars shorted together at the ends by two aluminum rings,
forming a squirrel-cage shaped circuit (squirrel-cage)
• Two basic design types depending on the rotor design
– SQUIRREL-CAGE: conducting bars laid into slots and shorted at both
ends by shorting rings.
– WOUND-ROTOR: complete set of three-phase windings exactly as the
stator. Usually Y-connected, the ends of the three rotor wires are
connected to 3 slip rings on the rotor shaft. In this way, the rotor
circuit is accessible.

65. Construction
Squirrel cage rotor
Wound rotor
Notice the
slip rings

66. Construction
Brushes
Slip rings

67. IMPORTANT PARTS IN I.M

68. Synchronous speed
POLES 50 Hz
2 3000
4 1500
6 1000
8 750
10 600
12 500

69. 3 PHASE WAVE FORM IN I.M

70. WOUND ROTOR TYPE I.M

71. SLIP
as slip.

74. Torque Vs Slip Characteristics

79. Comparison between Single Phase and Three Phase
Induction Motors
– Single phase induction motors are simple in construction,
reliable and economical for small power rating as
compared to three phase induction motors.
– The electrical power factor of single phase induction
motors is low as compared to three phase induction
motors.
– For same size, the single phase induction motors develop
about 50% of the output as that of three phase induction
motors.
– The starting torque is also low for asynchronous motors.
– The efficiency of single phase induction motors is less as
compare it to the three phase induction motors.

80. starter

81. Necessity of starter
• At starting ,the speed of motor is zero so that
the back e.m.f. In the armature is zero.
• Armature resistance is so low, if it is
connected to power supply directly ; huge
current will pass thru armature.
• The huge current may damage the machine,
major heat, very high speed in case of DC
series motor.
• Ia = V/Ra

82. Function of starter
• Start and stop the motor.
• Limit inrush current where necessary.
• Permit automatic control when required
• Protect motor and other connected
equipments from over voltage, no voltage,
under voltage, single phasing etc.

83. Motor Starter Features.
• Rated by current (amperes) or power
(horsepower)
• Remote ON/OFF control
• Motor overload protection
• Starting and stopping (electrical life)
• Plugging and jogging (rapid making and
breaking current)

84. Type of starter
for DC Motor
• Two point starter for DC series motor
• Three point starter for shunt motor
• Four point starter for compound motor
For AC Motor
• DOL Starter
• Star-Delta
• Auto-transformer
• Variable Frequency drive

85. Wiring Diagram of DOL Starter:

86. Motor Starting Characteristics on DOL Starter:
• Available starting current: 100%.
• Peak starting current: 6 to 8 Full Load
Current.
• Peak starting torque: 100%

87. Advantages of DOL Starter:
• Most Economical and Cheapest Starter
• Simple to establish, operate and maintain
• Simple Control Circuitry
• Easy to understand and trouble‐shoot.
• It provides 100% torque at the time of starting.
• Only one set of cable is required from starter to
motor.
• Motor is connected in delta at motor terminals.

88. Disadvantages of DOL Starter:
• It does not reduce the starting current of the
motor.
• High Starting Current: Very High Starting Current
(Typically 6 to 8 times the FLC of the motor).
• Mechanically Harsh: Thermal Stress on the
motor, thereby reducing its life.
• Voltage Dip: There is a big voltage dip in the
electrical installation
• High starting Torque: Unnecessary high starting
torque, even when not required by the load.

89. Suitability
DOL is Suitable for:
• Small water pumps, compressors, fans and
conveyor belts.
• Motor rating up to 5.5KW
DOL is not suitable for:
• The peak starting current would result in a
serious voltage drop on the supply system
• Motor rating above 5.5KW

90. Star delta starter
• Most induction motors are started directly on
line, but when very large motors are started that
way, they cause a disturbance of voltage on the
supply lines due to large starting current surges.
• To limit the starting current surge, large
induction motors are started at reduced voltage
and then have full supply voltage reconnected
when they run up to near rotated speed.

91. STAR -DELTA STARTER

92. Advantages of Star-Delta starter:
• The operation of the star-delta method is
simple and rugged
• It is relatively cheap compared to other
reduced voltage methods.
• Good Torque/Current Performance.
• It draws 2 times starting current of the full
load ampere of the motor connected

93. Disadvantages of Star-Delta starter:
• Low Starting Torque, only 33% starting torque
• Break In Supply – Possible Transients
• Six Terminal Motor Required (Delta Connected).
• It requires 2 set of cables from starter to motor.
• The delta of motor is formed in starter and not on motor terminals.
• Applications with a load torque higher than 50 % of the motor
rated torque will not be able to start using the start-delta starter.
• Low Starting Torque: reduction of the line voltage by a factor of
1/√3 (57.7%) to the motor and the current is reduced to 1/3 of the
current at full voltage, but the starting torque is also reduced 1/3
to 1/5 of the DOL starting torque .

94. Difference between DOL/Star delta /Autotransformer
Sr. DOL Starter Star delta starter Auto transformer
starter
1 Used up to 5 HP Used 5 HP to 20HP Used above 20 HP
2 Does not decrease
the starting current
Decreases the starting current
by 1/3 times
Decreases the starting
current as required
3 It is cheap It is costly It is more costly
4 It connects directly
the motor with
supply for starting
as well as for
running
It connects the motor first in
star at the time of starting in
delta for running
It connects the motor
according to the taping
taken out from the auto
transformer

95. Synchronous Motor - Construction
• Synchronous motor and induction motor are
the most widely used types of AC motor.
Construction of a synchronous motor is similar
to an alternator (AC generator). A
same synchronous machine can be used as a
synchronous motor or as an alternator.
Synchronous motors are available in a wide
range, generally rated between 150kW to
15MW with speeds ranging from 150 to 1800
rpm.

96. Synchronous Motor - Construction
Just like any other motor, it consists of a stator and a rotor. The stator core is constructed
with thin silicon lamination and insulated by a surface coating, to minimize the eddy
current and hysteresis losses. The stator has axial slots inside, in which three phase stator
winding is placed. The stator is wound with a three phase winding for a specific number of
poles equal to the rotor poles.
The rotor in synchronous motors is mostly of salient pole type. DC supply is given to the
rotor winding via slip-rings. The direct current excites the rotor winding and creates
electromagnetic poles. In some cases permanent magnets can also be used.

97. Working Of Synchronous Motor
• The stator is wound for the similar number of poles as that of rotor, and fed with
three phase AC supply. The 3 phase AC supply produces rotating magnetic field in
stator. The rotor winding is fed with DC supply which magnetizes the rotor.
Consider a two pole synchronous machine as shown in figure above

98. Construction
• Rotor: There are two types of rotor used in an AC generator /
alternator:
(i) Salient and (ii) Cylindrical type
• Salient pole type: Salient pole type rotor is used in low and medium
speed alternators. Construction of AC generator of salient pole
type rotor is shown in the figure above. This type of rotor consists
of large number of projected poles (called salient poles), bolted on
a magnetic wheel. These poles are also laminated to minimize the
eddy current losses. Alternators featuring this type of rotor are
large in diameters and short in axial length.
• Cylindrical type: Cylindrical type rotors are used in high speed
alternators, especially in turbo alternators. This type of rotor
consists of a smooth and solid steel cylinder havingg slots along its
outer periphery. Field windings are placed in these slots.

99. Principle of Operation Synchronous Motor
• Synchronous motor is a doubly excited machine i.e two electrical inputs are
provided to it. It’s stator winding which consists of a 3 phase winding is provided
with 3 phase supply and rotor is provided with DC supply.
• The 3 phase stator winding carrying 3 phase currents produces 3 phase rotating
magnetic flux. The rotor carrying DC supply also produces a constant flux.
• Considering the frequency to be 50 Hz, from the above relation we can see that
the 3 phase rotating flux rotates about 3000 revolution in 1 min or 50 revolutions
in 1 sec.
• At a particular instant rotor and stator poles might be of same polarity (N-N or S-S)
causing repulsive force on rotor and the very next second it will be N-S causing
attractive force. But due to inertia of the rotor, it is unable to rotate in any
direction due to attractive or repulsive force and remain in standstill condition.
Hence it is not self starting.
• To overcome this inertia, rotor is initially fed some mechanical input which rotates
it in same direction as magnetic field to a speed very close to synchronous speed.
After some time magnetic locking occurs and the synchronous motor rotates in
synchronism with the frequency.

100. EMF EQUATION OF SYNCHRONOUS
MOTOR

102. Main Features of Synchronous Motors
• Synchronous motors are inherently not self starting. They require
some external means to bring their speed close to synchronous speed
to before they are synchronized.
The speed of operation of is in synchronism with the supply
frequency and hence for constant supply frequency they behave as
constant speed motor irrespective of load condition
This motor has the unique characteristics of operating under
any electrical power factor. This makes it being used in electrical
power factor improvement.

103. Application of Synchronous Motor
• Synchronous motor having no load connected to its shaft is
used for power factor improvement. Owing to its
characteristics to behave at any electrical power factor, it is
used in power system in situations where static capacitors
are expensive.
• Synchronous motor finds application where operating
speed is less (around 500 rpm) and high power is required.
For power requirement from 35 kW to 2500 KW, the size,
weight and cost of the corresponding three phase induction
motor is very high. Hence these motors are preferably
used. Ex- Reciprocating pump, compressor, rolling mills etc.