Electrical Machines

LSEGG216A9080V

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

AssessmentAssessmentTheory Test 1Theory Test 2Practical Test

QuizzesTheory Test 3

1015251040 MUST PASSMUST PASS

Transformer Transformer ConstructionConstruction

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

Transformer Transformer UsesUsesChanging

Isolation

• Voltage Levels• Current Levels• Impedance values

Transformer Transformer OperationOperation 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 Transformer OperationOperation Primary coil normally has a subscript of 1

Secondary coil has a subscript of 2

V1 V2

I1 I2

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

Core TypeCore TypeOne Magnetic Circuit

Shell TypeShell TypeTwo Magnetic Circuits

Toroidal CoreToroidal Core

LaminationsLaminationsWhy not just solid steel?Eddy Currents

Why do we laminate the core?

I

S

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

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

Losses due to Eddy Currents

21mee tBfKP

Pe

Ke

FBm

t1

= losses in W/m3

= Constant= Frequency= Maximum Flux density= Lamination thickness

Hysteresis CurveHysteresis Curve•Bigger the area covered, the more losses

associated with Iron losses

Steel TypesSteel TypesSilicon 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 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

Grain SizeGrain SizeThe 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 Steellosses 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

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

MagnetostrictionA 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"

Winding typesWinding types•Three types?•Magnetic leakage

ConcentricHigher voltage closest to Iron

Winding typesWinding typesSandwich or Pancake

Very high voltages on both windings

Winding typesWinding typesSide by Side

Very good insulation between windings

Insulation of Insulation of windingswindings

• Lacer• Oil

•Traditionally a highly-refined (naphthenic) mineral oil •Polychlorinated Biphenyls PCBs

Transformer Transformer TanksTanks

Nameplate DetailsNameplate Details