Introduction to Electrical Machinery

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

• Generators AC, DC

• Motors AC (Single Phase, Three Phase), DC

• Transformers AC (Single Phase, Three Phase)

• Transfers energy from one electrical circuit to another without change in frequency.

• Static Device working on principle of electromagnetic induction

• Electric Circuits linked by common magnetic core

• Applications Electric power systems

Power transmission, Distribution Networks

Electronic Circuits

Electric Traction

Transformers

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

Primary Side Secondary Side

Core

V1Supply side V2 Load sideN1

N1 = Number of turns on primary

N2

N2 = Number of turns on secondary

Representation

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

Physical Model

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

I1

E1E1 E2

E2 V2V2

I2

LOADV1

V1

Ø

• Magnetic Core : Flux path

• Flux Linkages : Primary & Secondary

• Induced Emf : Primary – Self Induced Emf & Secondary – Mutually Induced Emf

Operation

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

YokeYoke

LV windingLV winding

InsulationInsulation

HV windingHV winding

LimbsLimbs

CoreWinding crossover

Primary &Secondary windings

LaminationsLaminations

Construction – Core Type

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

Side LimbsSide Limbs

Central LimbCentral Limb LV windingLV winding

InsulationInsulation

HV windingHV winding

YokeYoke

Core

InsulationSecondary

Winding

Yoke

Terminals

LaminationsLaminations

Construction - Shell Type

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

t sin ,Core flux m

)2

πt(sinNω

dt

dNf, eInduced em m

11111 2 ),2

sin( NfNEtEe mmmm where

m11 f N 44.4E , Emf InducedPry

m22 f N 44.4E , Emf Induced Sec

emf equation

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

2

φNf2

2

EEEmfinducedSelfofvalueRMS

ωφNEEmfinducedselfofvalueMaximum

m11max1

m11max

k1

2

1

2

N

N

E

E(Transformation Ratio)(Transformation Ratio)

N2 > N1 : Step Up type

N1 N2

V1 V2

E2 > E1

V2 > V1, I1 > I2

V1 V2

N2 = N1 : 1:1 type

E2 = E1

V2 = V1, I1 = I2

N2 < N1 : Step down type

V1 V2

E2 < E1

V2 < V1, I1 < I2

Transformation Ratio

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal

A 250 kVA, 11000 / 415 V, 50 Hz, 1 transformer has 80 turns on the secondary. Determine (a) rated primary and secondary currents (b) primary turns (c) maximum flux (d) emf induced per turn

Ans: (a) 22.73 A, 602.41 A (b) 2120 turns (c) 23.37 mWb (d) 5.1886 Volts /

turn

Exercise

ELE 101 / 102 Basic Electrical Technology Dept of E & E, MIT Manipal