Construction of transformer

1. 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
• 3φ Induction Motors Operating Principles
• 3φ Induction Motors Construction
• 3φ Induction Motors Characteristics
• 1φ Induction Motors Split Phase
• 1φ Induction Motors Capacitor & Shaded pole
• 1φ Motors Universal
• Motor Protection
• 3φ Synchronous Machines
• Alternators & Generators

3. AssessmentAssessment
Theory Test 1
Theory Test 2
Practical Test
Quizzes
Theory Test 3
10
15
25
10
40 MUST PASSMUST PASS

4. Transformer ConstructionTransformer Construction

5. IntroductionIntroduction
 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

6. Transformer UsesTransformer Uses
Changing
Isolation
• Voltage Levels
• Current Levels
• Impedance values

7. Transformer OperationTransformer 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 OperationTransformer Operation
 Primary coil normally has a subscript of 1
 Secondary coil has a subscript of 2
V1 V2
I1 I2

9. Core TypesCore Types
• Core Construction
• Steel type
• Laminations
• core type
• Shell type
• Toroidal

10. Core TypeCore Type
One Magnetic Circuit

11. Shell TypeShell Type
Two Magnetic Circuits

12. Toroidal CoreToroidal Core

13. LaminationsLaminations
Why not just solid steel?
Eddy Currents

14. Why do we laminate the core?
I
S

15. Why do we laminate the core?
I
S
Large Number of flux lines cut
∴High voltage generated across core
Eddy currents are large & losses are great

16. Why do we laminate the core?
I
S
Small Number of flux lines cut
∴Low voltage generated across core
Eddy currents are small & losses are reduced

17. Losses due to Eddy Currents
( )2
1mee tBfKP =
Pe
Ke
F
Bm
t1
= losses in W/m3
= Constant
= Frequency
= Maximum Flux density
= Lamination thickness

18. Hysteresis CurveHysteresis Curve
• Bigger the area covered, the more losses
associated with Iron losses

20. Steel TypesSteel 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

21. Grain OrientationGrain 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
• 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
Non-orientated

22. Grain SizeGrain 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

23. Amorphous Steel
losses up to 30% of conventional steels
Made by pouring molten alloy steel on a rotating cooled wheel.
• high cost (about twice that of conventional silicon steel)
• lower mechanical properties
This cools the metal so quickly that crystals do not form

24. 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

26. Magnetostriction
A property of ferromagnetic materials that causes them to
change their shape when subjected to a magnetic field
losses due to frictional heating
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
The effect is responsible for the familiar "electric hum"

27. Winding typesWinding types
• Three types?
• Magnetic leakage
Concentric
Higher voltage closest to Iron

28. Winding typesWinding types
Sandwich or Pancake
Very high voltages on both windings

29. Winding typesWinding types
Side by Side
Very good insulation between windings

30. Insulation of windingsInsulation of windings
• Lacer
• Oil
• Traditionally a highly-refined (naphthenic) mineral oil
• Polychlorinated Biphenyls PCBs

31. Transformer TanksTransformer Tanks

32. Nameplate DetailsNameplate Details