1. Hansaba College of Engineering & Technology
Subject : D.C. Machine & Transformer
Topic : Transformer
Name : Pandya Bhrugu
:Rathod Jaydipsinh
: Nai Maulik

2. Electrical Machines

3. 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

4. Transformer Uses Changing Voltage Levels Current Levels
Impedance values

5. 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+

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

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

8. Core Type
One Magnetic Circuit

9. Shell Type
Two Magnetic Circuits

10. Toroidal Core

11. Laminations
Why not just solid steel? Eddy Currents

12. Why do we laminate the core?S

13. 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

14. 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

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

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

18. 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

19. 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

20. 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

22. 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"

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

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

25. Winding types
Side by Side
Very good insulation between windings

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

27. Transformer Tanks

28. Thank You