Electrical Machines

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Electrical Machines

• LSEGG216A
• 9080V

2
Content of Course

• Transformer Construction
• Transformer Operation
• Transformer Losses, Efficiency Cooling
• Transformer Voltage Regulation Impedance
• Parallel Operation Auxiliary Equipment
• Auto Transformers Instrument Transformers
• 3? Induction Motors Operating Principles
• 3? Induction Motors Construction
• 3? Induction Motors Characteristics
• 1? Induction Motors Split Phase
• 1? Induction Motors Capacitor Shaded pole
• 1? Motors Universal
• Motor Protection
• 3? Synchronous Machines
• Alternators Generators

3
Assessment

• Theory Test 1
• Theory Test 2
• Practical Test
• Quizzes
• Theory Test 3

10 15 25 10 40
MUST PASS
4
Transformer Construction
5
Introduction

• Describe the construction of the various types of
  lamination style and core construction used in
  single phase, three phase, auto and instrument
  transformers.
• Identify the different winding styles/types used
  in transformers.
• State the methods used to insulate low and high
  voltage transformers.
• Describe the construction of transformer tanks
  for distribution transformers.
• List the types of information stated on
  transformer nameplates.
• Perform basic insulation resistance, continuity
  and winding identification tests

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Transformer Uses

• Changing
• Isolation

• Voltage Levels
• Current Levels
• Impedance values

7
Transformer Operation

• Primary coil is supplied with a AC voltage.
• Current drawn produces a magnetic field
• Magnetic field transported to a secondary coil
  via a magnetic circuit
• Magnetic field induces a voltage in secondary
  coil

V
V
8
Transformer Operation

• Primary coil normally has a subscript of 1
• Secondary coil has a subscript of 2

I1
I2
V1
V2
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Core Types

• Core Construction
• Steel type
• Laminations
• core type
• Shell type
• Toroidal

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Core Type
One Magnetic Circuit
11
Shell Type
Two Magnetic Circuits
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Toroidal Core
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Laminations

• Why not just solid steel?
• Eddy Currents

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Why do we laminate the core?
I
S
15
Why do we laminate the core?
Eddy currents are large losses are great

• Large Number of flux lines cut
• High voltage generated across core

I
S
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Why do we laminate the core?
Eddy currents are small losses are reduced

• Small Number of flux lines cut
• Low voltage generated across core

I
S
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Losses due to Eddy Currents
Pe Ke F Bm t1
losses in W/m3 Constant Frequency Maximum
Flux density Lamination thickness
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Hysteresis Curve

• Bigger the area covered, the more losses
  associated with Iron losses

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Steel Types

• Silicon steel is used for laminations

Silicon content 0 6.5
Why Silicon?

• Small hysteresis curve area
• Increases electrical resistivity

Reduced eddy current size

• Hardened grain structure
• Reduced workability

• Very low carbon levels lt0.005 are called for or
  magnetic ageing will take place

Losses will increase with age

• Carbon can be removed by annealing in a hydrogen
  rich atmosphere

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Grain Orientation

• Optimum properties are developed in the rolling
  direction
• Magnetic density is increased by 30 in the coil
  rolling direction
• Magnetic saturation is decreased by 5
• Given codes such as M-0, M1, M-2, M-3, M-4 and
  M-6

Non-orientated

• Similar magnetic properties in all directions
• less expensive
• Used in applications where the direction of
  magnetic flux is changing (motors and generators)
• Given codes from M-15 to M-47

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Grain Size

• The larger the grain the less the hysteresis
  losses

2-10 W/kg _at_ 60 Hz and 1.5 tesla magnetic field
strength are common with a 150µm grain size
heat treatment increases the average crystal size
Excessive bending, incorrect heat treatment, or
even rough handling of core steel can adversely
effect its magnetic properties
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Amorphous Steel

• losses up to 30 of conventional steels

Made by pouring molten alloy steel on a rotating
cooled wheel.
This cools the metal so quickly that crystals do
not form

• high cost (about twice that of conventional
  silicon steel)
• lower mechanical properties

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Lamination Coatings

• Increase electrical resistance between
  laminations
• Provide resistance to corrosion
• Act as a lubricant during die cutting

• Can be organic or inorganic (such as Magnesium
  oxide)
• Dependant on the heat treatment of the
  laminations
• Wheather it is immersed in oil
• The working temperature of the finished item

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Magnetostriction

• A property of ferromagnetic materials that causes
  them to change their shape when subjected to a
  magnetic field

first identified in 1842 by James Joule
When a magnetic field is applied, the boundaries
between the domains shift and the domains rotate,
both these effects causing a change in the
material's dimensions
losses due to frictional heating
The effect is responsible for the familiar
"electric hum"
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Winding types

• Three types?
• Magnetic leakage

Concentric
Higher voltage closest to Iron
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Winding types
Sandwich or Pancake
Very high voltages on both windings
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Winding types
Side by Side
Very good insulation between windings
30
Insulation of windings

• Lacer
• Oil

• Traditionally a highly-refined (naphthenic)
  mineral oil
• Polychlorinated Biphenyls PCBs

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Transformer Tanks
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Nameplate Details