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
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 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

6. 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

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

10. Core Type
One Magnetic Circuit

11. Shell Type
Two Magnetic Circuits

12. Toroidal Core

13. Laminations
Why not just solid steel? Eddy Currents

14. Why do we laminate the core?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

16. 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

17. Losses due to Eddy CurrentsPe Ke F Bm t1
= losses in W/m3
= Constant
= Frequency
= Maximum Flux density
= Lamination thickness

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

20. Reduced eddy current size Losses will increase with age
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

21. Grain Orientation Non-orientated
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

22. Grain Size The larger the grain the less the hysteresis losses
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.
This cools the metal so quickly that crystals do not form
high cost (about twice that of conventional silicon steel)
lower mechanical properties

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. first identified in 1842 by James Joule
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"

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

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

29. 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

31. Transformer Tanks

32. Nameplate Details