UNIT I

EE 1403 DESIGN OF

ELECTRICAL APPARATUS

BY

V.BALAJI, B.E. M.Tech, (Ph.D), MIEE, MISTE, MIAENG. Asst.Professor

EEE

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

D.C. MACHINES

Constructional details – output equation –

main dimensions - choice of specific

loadings – choice of number of poles –

armature design – design of field poles

and field coil – design of commutator and

brushes – losses and efficiency

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 9

Constructional 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 BOOKS

1. 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 BOOKS

1. 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 Publications

Unit

Unit

-

_-

1

₁

MAGNETIC CIRCUITS AND

COOLING OF ELECTICAL

MACHINES

BY

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

EEE

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

Classification of design

Dielectric design → design of insulators

Electromagnetic design:

Stator & Rotor

Rotating machine 1. Core

2. Teeth dimension 3. Winding & air gap

Stationary

Core & winding

Mechanical design: Rotating Frame Shaft bearings 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

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 π φ D IzZ ac 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 cktckt The 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 Circuits Magnetic Circuits Electric Circuits Electric Circuits S.N S.N o o

Contd

Contd

…

_…

.

_.

Flux density = Flux/

Flux density = Flux/

area area Current density = Current density = current/area current/area 5. 5. Flux = Flux = mmfmmf / / Relutance Relutance

Current = EMF/ Resistance

Current = EMF/ Resistance

4. 4. Magnetic Circuits Magnetic Circuits Electric Circuits Electric Circuits S.N S.N o o

Differences between Electric and Magnetic

Differences between Electric and Magnetic

Circuits

Circuits

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 Circuits Magnetic Circuits Electric Circuits Electric Circuits S. S. No No

Magnetic

circuit:-1. It provides path for flux lines 2. mmf creates flux against

Reluctance calculate:- in smooth armature

y_s Pole surface Closed slots Armature surface w_s W_s – width of slot W_t – width of tooth

(i) For smooth armature closed type of slot are chosen

Reluctance in open type of

slot:-W_{s W}

t

l_g

y_s

(without fringing flux ) flux liner g o g g

A

l

s

A

l

s

µ

µ

=

=

A

l

s

µ

=

Semi closed type:-t g L w A = ×

(

)

(

)

µ

L

y

A

A

l

S

×

′

=

=

µ

(

y

w

)

w

L

×

−

=

(

)

w

y

L

l

S

−

=

µ

Reluctance in open type of slots (with fringing flux ):-s s t t s s s t s s g g o g g w y w w w y w w y L y A A l S − = ⇒ + = + = ′ × ′ = = δ µ ω_s ω_t l_g y_s y_s' fringing flux ω_s

( )

δ

ω

δω

ω

−

−

=

′

+

−

=

′

1

y

y

y

y

( )

kcs

w

y

−

=

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

Empirical

relation:-ksc (semi closed slots) = Open slots:-w Sl_g / 1 1 + g o

l

w

y

y

y

kcs

2

1

log

1

tan

2

=









+

−

=

π

π