TRANSFORMERS AND SPECIAL MACHINES (QUALITATIVE TREATMENT ONLY)

1. UNIT 5- TRANSFORMERS AND SPECIAL
MACHINES (QUALITATIVE TREATMENT
ONLY)
Constructional, Principle and Working of operation of Single Phase
Transformer - EMF Equation – Applications - Auto Transformer - Special
Machines: Stepper motor- Permanent Stepper Motor – Variable Reluctance
Stepper Motor – Servomotor - AC Servomotor - DC Servomotor – Stepper
Motor Selection and Control : An Industrial Case Study.
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2. Single Phase Transformer
• The transformer is a device that transfers electrical energy from
one electrical circuit to another electrical circuit without change
in frequency.
• The two circuits may be operating at different voltage levels but
always work at the same frequency.
• Basically transformer is an electro magnetic energy conversion
device. It is commonly used in electrical power system and
distribution systems.
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3. Working Principle of Transformer
• The basic principle behind working of a
transformer is the phenomenon of mutual
induction between two windings linked by
common magnetic flux.
• It consists of two winding. The coil to which the
supply is given is called Primary winding.
• The winding to which the load is connected is
called Secondary winding.
• When, primary winding is connected to a
source of alternating voltage,
alternating magnetic flux is produced around
the winding.
• The core provides magnetic path for the flux, to
get linked with the secondary winding.
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4. • Most of the flux gets linked with the secondary
winding which is called as 'useful flux' or main
'flux', and the flux which does not get linked
with secondary winding is called as 'leakage
flux'.
• As the flux produced is alternating (the
direction of it is continuously changing), EMF
gets induced in the secondary winding
according to Faraday's law of electromagnetic
induction.
• This emf is called 'mutually induced emf', and
the frequency of mutually induced emf is same
as that of supplied emf.
• If the secondary winding is closed circuit, then
mutually induced current flows through it, and
hence the electrical energy is transferred from
one circuit (primary) to another circuit
(secondary).
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6. Construction of Transformer
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7. Construction of Transformer
• Two basic parts of a transformer are i) core , ii) winding
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8. Lamination – L I E U
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9. Core type transformer
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10. Shell type transformer
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11. Windings of a transformer
i) Concentric windings ii) Sandwich windings
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13. Difference between Core and shell type
transformer
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14. Comparison of Core and Shell type
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15. EMF equation of transformer
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16. EMF equation of transformer
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19. Voltage transformation ratio of transformer
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21. Applications of single phase transformer
• Step-down localized power distribution
• Television sets to regulate voltage
• Low voltage electronic devices
• Step-up power in home inverters
• Non-urban areas where electrical demand is lower
• Commercial and residential lighting and heating equipment
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22. Auto Transformer
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25. Equation for copper saving in Auto
Transformer
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29. Advantage of Autotransformer
• Copper required is less
• Efficiency is comparatively high
• Size and cost is comparatively less
• Copper loss is less
• Smooth and continuous variation of voltage is possible
• Voltage regulation is higher than the two winding transformer
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30. Limitation of Autotransformer
• There is no electrical separation between primary and secondary
which is risky in case of high voltage levels.
• Economical only when voltage ratio is less than 2.
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31. Application of Autotransformer
• Used as a starter for safely starting induction motor and synchronous
motor.
• Booster at the end of long transmission line to compensate for line
losses
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32. STEPPER MOTOR
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33. • A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical
movements.
• Stepper motor rotates in discrete step increments when electrical command pulses are applied to it.
• The sequence of the applied pulses is directly related to the direction of motor shafts rotation.
• The angle through which the stepper motor shaft rotates for application of each command pulse is
called step angle (β).
• Where Ns= No.of stator teeth or pole; Nr= No. of rotor teeth or pole; m=No. of phases. The
opposite poles of stator windings are connected in series considered to be one phase.
• The No. of steps required to complete one revolution is resolution (Z)
Z= No. of steps/ one revolution= 360 degree/ β
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STEPPER MOTOR

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35. Variable Reluctance stepper motor
• It is constructed from ferromagnetic material with salient pole.
• Stator is made from stack of steel lamination and equally spaced
six inward projecting pole each wounded with exciting coil.
• Rotor also made from stack of steel lamination and equally
spaced four outward projecting pole.
• In stator opposite poles are connected in series considered as
one phase. Here it is three phase (A,B,C) or 6/4 VR stepper
motor.
• Each phase is excited separately through a switch by the DC
source.
• The direction of rotation of the stepper Motor depends upon the
sequence we excite the windings.
• Generally, number of stator poles will not be equal to number of
rotor poles for proper operation.
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36. Variable Reluctance Stepper Motor
• The principle of Variable Reluctance Stepper Motor is based on the
property of the flux lines which capture the low reluctance path.
• The stator and the rotor of the motor are aligned in such a way that
the magnetic reluctance is minimum.
•
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• The operation is based on various reluctance positions of rotor with
respect to stator.
• When any one phase of the stator is excited, it produces its magnetic
field whose axis lies along the poles of the phase which is excited.
• Then the rotor moves to minimum reluctance position.
• Let us see the operation of the VR stepper Motor ,when the phases
A,B,C are excited in sequence i.e., one after the other with the help of
switches S1,S2 and S3.
• When the phase AA1 is excited with the switch S1 closed, then stator
Magnet Axis exist along the poles formed due to AA1 (i.e) vertically.
• Then the rotor adjust itself in a minimum reluctance position and
occupies along AA1  1, 3, rotor poles. This is the initial position (ie)
0°.
• When the BB1 phase is excited with the switch S2 closed, and de-
energise the AA1 phase with the switch S1 opened, turns through 30°
step angle in clockwise direction.

39. •  =360/MxNr degree
• Where
• M = the number of stator phase
• Nr= the number of rotor phase
• In the present case M=3, Nr=4
•  =360/3x4 degree = 30 degree
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40. Variable reluctance stepper motor(full step
operation)
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41. Half step operation (A, AB,B,BC,C,CA)
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Summarisation of variable reluctance stepper motor

43. Permanent magnet Stepper Motor
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44. Step angle calculation for permanent magnet
stepper motor
• =360/MxNr degree
• Where
• M = the number of stator phase
• Nr= the number of rotor phase
• In the present case M=2, Nr=2
•  =360/2x2 degree = 90 degree
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46. Permanent magnet Stepper Motor
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47. Hybrid Stepper Motor
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48. Hybrid Stepper Motor
• Step angle  = (Nr-Ns)*360 / (Nr*Ns)
• Nr- no.of rotor teeth
• Ns- no.of stator teeth
• Nr=5
• Ns=4
• Step angle  =(5-4) * 360 / (5*4) = 18o
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49. Servo Motor
• A servomotor is a linear actuator or rotary actuator that allows for
precise control of linear or angular position, acceleration, and
velocity.
• A servomotor (or servo motor) is a simple electric motor, controlled
with the help of servomechanism.
• It consists of a motor coupled to a sensor for position feedback. It
also requires a relatively sophisticated controller, often a dedicated
module designed specifically for use with servomotors.
• If the motor as a controlled device, associated with servomechanism
is DC motor, then it is commonly known as a DC Servo Motor. If AC
operates the controlled motor, it is known as a AC Servo Motor.
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50. Servomechanism
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51. • There are some special types of applications of an electric motor
where the rotation of the motor is required for just a certain angle.
• For these applications, we require some special types of motor with
some special arrangement which makes the motor rotate a certain
angle for a given electrical input (signal).
• The servo motor is usually a simple DC motor controlled for specific
angular rotation with the help of additional servomechanism.
• The main reason behind using a servo is that it provides angular
precision, i.e. it will only rotate as much we want and then stop and
wait for the next signal to take further action.
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52. Servo System
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53. DC Servo Motor
• The motors which are utilized as
DC servo motors, generally have
separate DC source for field
winding and armature winding.
• The control can be achieved
either by controlling the field
current or armature current.
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54. Field Controlled DC Servo Motor
• In this arrangement the field of
DC motor is excited be the
amplified error signal and
armature winding is energized
by a constant current source.
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55. Armature Controlled DC Servo Motor
• Here the armature is energized
by amplified error signal and
field is excited by a constant
current source.
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56. AC Servomotor
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57. AC Servomotor
• The control phase is usually
supplied from a servo amplifier.
• The speed and torque of the rotor
are controlled by the phase
difference between the control
voltage and the reference phase
voltage.
• By reversing the phase difference
from leading to lagging or vice
versa, the direction of the rotation
of the rotor can be reversed.
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58. Application of servo motor
• Remote-controlled toy cars for controlling the direction of motion
• Widely used as the motor which moves the tray of a CD or DVD
player.
• Solar Tracking System
• Servo motors control industrial spinning and weaving machines
• Printing Presses/Printers
• Automatic Door Openers
• Robotic Vehicle
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59. Thank you
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