Basics of Electrical Machine Design

EE 1403 DESIGN OF ELECTRICAL APPARATUS

BY

V.BALAJI, B.E. M.Tech, (Ph.D), MIEE, MISTE, MIAENG.Asst.ProfessorEEEDhanalakshmi College of Engg

1. MAGNETIC CIRCUITS AND COOLING OF ELECTICAL MACHINES

� Concept of magnetic circuit – MMF calculation for various types of electrical machines – real and apparent flux density of rotating machines –leakage reactance calculation for transformers, induction and synchronous machine - thermal rating: continuous, short time and intermittent short time rating of electrical machines-direct and indirect cooling methods – cooling of turbo alternators.

i. To study mmf calculation and thermal rating of various types of electrical machines.

ii. To design armature and field systems for D.C.machines.

iii. To design core, yoke, windings and cooling systems of transformers.

iv. To design stator and rotor of induction machines.

v. To design stator and rotor of synchronous machines and study their thermal

SYALLBUS

D.C. MACHINES

Constructional details – output equation –main dimensions - choice of specificloadings – choice of number of poles –armature design – design of field polesand field coil – design of commutator and brushes – losses and efficiencycalculations.

TRANSFORMERS Constructional details of core and shell type transformers – output rating of single phase and three phase transformers – optimum design of transformers – design of core, yoke z and windings for core and shell type transformers – equivalent circuit parameter from designed data – losses and efficiency calculations – design of tank and cooling tubes of transformers.

THREE PHASE INDUCTION MOTORS Constructional details of squirrel cage and slip ring motors – output equation –main dimensions – choice of specific loadings –design of stator – design of squirrel cage and slip ring rotor – equivalent circuit parameters from designed data – losses and efficiency calculations.

SYNCHRONOUS MACHINES 9Constructional details of cylindrical pole and salient pole alternators – output equation – choice of specific loadings –main dimensions – short circuit ratio –design of stator and rotor of cylindrical pole and salient pole machines - design of field coil - performance calculation from designed data - introduction to computer aided design.

TEXT BOOKS1. A.K. Sawhney, ‘A Course in Electrical Machine Design’, Dhanpat Rai and Sons, New Delhi, 1984.2. S.K. Sen, ‘Principles of Electrical Machine Design with Computer Programmes’,Oxford and IBH Publishing Co.Pvt Ltd., New Delhi, 1987.

REFERENCE BOOKS1. R.K. Agarwal, ‘Principles of Electrical Machine Design’, S.K.Kataria and Sons,Delhi, 2002.2. V.N. Mittle and A. Mittle, ‘Design of Electrical Machines’, Standard Publicationsand Distributors, Delhi, 2002.

Unit Unit --11

MAGNETIC CIRCUITS AND COOLING OF ELECTICAL

MACHINES

BY

V.BALAJI, B.E. M.Tech, (Ph.D), MIEEE, MISTE, MIAENG.

Asst.Professor

EEE

Dhanalakshmi College of Engg

INTRODUCTION INTRODUCTION

Definition :-

Design may be defined as a creative physical

realisation of theoretical concepts

Engineering design is the application of Science,

Technology and inventions to produce Various

machines to solve specified tasks with optimum

efficiency and economy.

The major considerations of a good design

� Cost effective

� Durable

� Quality

� Efficient

� Classification of design� Electromagnetic design

� Mechanical design

� Thermal design

� Dielectric design → design of insulators


Electromagnetic design:

Stator & Rotor

Rotating machine

1. Core

2. Teeth dimension

3. Winding & air gap

Stationary

Core & winding

V.BALAJI AP/EEE DCE

Mechanical design:

Rotating

FrameShaftbearings

Stationary

Tank (Transformer tank)


General design procedure

Main dimensions (decides voltage rating of the machine)

Rotating

D- diameter of armature (or) stator

L- Length of armature (or) stator are length.

Stationary:

Hw – height of the window

Hw – width of the window

Main dimensions depend on loading of the machine

ie

D & L α loading

Window

Total electric loading:

Total number of armature ampere conductors

the air gap (or) around the armature face.

Specific magnetic loading

Bav =

Specific electrical loading (ac)

DL

p

πφ

D

IzZac

π=

Similarities in Electric & Magnetic Similarities in Electric & Magnetic

circuits.circuits.

The path of flux is The path of flux is

called magnetic called magnetic cktcktThe path of Current is called The path of Current is called

electric electric cktckt..3.3.

The creation of flux is The creation of flux is

opposed by reluctance opposed by reluctance

of the of the cktckt..

Flow of current is opposed Flow of current is opposed

by resistance of the circuit.by resistance of the circuit.2.2.

The The mmfmmf creates flux creates flux

in a closed path.in a closed path.The The emfemf circulatescirculates

Current in a closed path.Current in a closed path.

1.1.

Magnetic CircuitsMagnetic CircuitsElectric CircuitsElectric CircuitsS.NS.N

oo


ContdContd……..

Flux density = Flux/ Flux density = Flux/

areaareaCurrent density = Current density =

current/area current/area 5.5.

Flux = Flux = mmfmmf / /

RelutanceRelutanceCurrent = EMF/ ResistanceCurrent = EMF/ Resistance4.4.

Magnetic CircuitsMagnetic CircuitsElectric CircuitsElectric CircuitsS.NS.N

oo


Differences between Electric and Magnetic Differences between Electric and Magnetic

CircuitsCircuits

Reluctance depends Reluctance depends

on total flux or flux on total flux or flux

density in the material.density in the material.

Resistance is independent of Resistance is independent of

current strength. current strength. 3.3.

Energy is needed only Energy is needed only

to create the flux but to create the flux but

not to maintain it.not to maintain it.

When current flows, the When current flows, the

energy is spent continuously. energy is spent continuously. 2.2.

Flux does not flow, Flux does not flow,

but it is only assumed but it is only assumed

to flow to flow

Current actually flows in the Current actually flows in the

electric electric cktckt..1.1.

Magnetic CircuitsMagnetic CircuitsElectric CircuitsElectric CircuitsS.S.

NoNo


Magnetic circuit:-

1. It provides path for flux lines

2.mmf creates flux against

Reluctance calculate:- in smooth armature

ysPole surface

Closed slotsArmature surfacews

Ws – width of slot

Wt – width of tooth

(i) For smooth armature closed type of slot are chosenV.BALAJI, B.E. M.Tech, (Ph.D), MIEEE, MISTE, MIAENG.

Reluctance in open type of slot:-

Ws Wt

lg

ys

(without fringing flux )

flux liner

go

gg A

ls

A

ls

µ

µ

=

=

A

ls

µ=


Semi closed type:-

tg wLA ×=

( )ss wyL −×=

( )sso

gg wyL

LS

−=

µ

wt wsws

lg

ys

ys’Fringing flux


LyA

A

lS

sg

go

gg

×′=

=µ

( )ss wywL −×=

( )oso

gg wyL

lS

−=

µ


Reluctance in open type of slots (with fringing flux ):-

ssttss

sts

sg

go

gg

wywwwy

wwy

LyA

A

lS

−=⇒+=+=′×′=

=

δ

µ

ωs ωt

lg

ys

ys'fringing flux

ωs

( )δωδωω−−=′

+−=′1sss

ssss

yy

yy

( )kcswy ss −=Kcs – carter’s coefficient

Sg = lg/µoL(ys – kcs ws)

Gap contraction factor:- (kgs)

It is defined as the ratio between reluctance of air gap with slotted armature to reluctance of air gap with smooth armature.

Empirical relation:-

ksc (semi closed slots) =

Open slots:-wSlg /1

1

+

g

o

l

wy

yykcs

2

1log1

tan2 21

=

+−= −

ππ













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Basics of Electrical Machine Design