Date post: | 29-Mar-2015 |
Category: |
Documents |
Upload: | estefany-maine |
View: | 272 times |
Download: | 6 times |
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