Hansaba College of Engineering & Technology Subject : D.C. Machine & Transformer Topic : Transformer Name : Pandya Bhrugu -130980109003 :Rathod Jaydipsinh-130980109017 : Nai Maulik -130980109029

Electrical Machines

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

Transformer Uses Changing Voltage Levels Current Levels Impedance values

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+

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

Core Types 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? S

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

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

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

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

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

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 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

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"

Winding types Concentric Three types? Magnetic leakage 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

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