Transcript Electrical Machines LSEGG216A 9080V

Electrical Machines
LSEGG216A
9080V
Content of Course
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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
Assessment
Theory Test 1
Theory Test 2
Practical Test
Quizzes
Theory Test 3
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10
40 MUST PASS
Transformer Construction
Introduction
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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
Transformer Uses
Changing
Isolation
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Voltage Levels
Current Levels
Impedance values
Transformer Operation
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Primary coil is supplied with a AC voltage.
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Current drawn produces a magnetic field
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Magnetic field transported to a secondary coil via a
magnetic circuit
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Magnetic field induces a voltage in secondary coil
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V+
Transformer Operation
 Primary coil normally has a subscript of 1
 Secondary coil has a subscript of 2
I1
V1
I2
V2
Core Types
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Core Construction
Steel type
Laminations
core type
Shell type
Toroidal
Core Type
One Magnetic Circuit
Shell Type
Two Magnetic Circuits
Toroidal Core
Laminations
Why not just solid steel?
Eddy Currents
Why do we laminate the core?
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Why do we laminate the core?
Eddy currents are large & losses are great
Large Number of flux lines cut
High voltage generated across core
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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
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Losses due to Eddy Currents
Pe  K e f Bm t 1 
2
Pe = losses in W/m3
Ke = Constant
F = Frequency
Bm = Maximum Flux density
t1 = Lamination thickness
Hysteresis Curve
• Bigger the area covered, the more losses
associated with Iron losses
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 <0.005% 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
Grain Orientation
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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
Grain Size
The larger the grain the less the hysteresis losses
2-10 W/kg @ 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
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
Lamination Coatings
• Increase electrical resistance between laminations
• Provide resistance to corrosion
• Act as a lubricant during die cutting
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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
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"
Winding types
• Three types?
• Magnetic leakage
Concentric
Higher voltage closest to Iron
Winding types
Sandwich or Pancake
Very high voltages on both windings
Winding types
Side by Side
Very good insulation between windings
Insulation of windings
• Lacer
• Oil
• Traditionally a highly-refined (naphthenic) mineral oil
• Polychlorinated Biphenyls PCBs
Transformer Tanks
Nameplate Details