UNIT I

EE 1403 DESIGN OF ELECTRICAL APPARATUS BY V.BALAJI, B.E. M.Tech, (Ph.D), MIEE, MISTE, MIAENG. Asst.Professor EEE Dhanalakshmi 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.

SYALLBUS

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 calculations.

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 and Distributors, Delhi, 2002.

Unit -1 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 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 V.BALAJI, B.E. M.Tech, (Ph.D), MIEEE, MISTE, MIAENG.

Electromagnetic design: Stator & Rotor

Rotating machine

Stationary

1. Core 2. Teeth dimension

Core & winding

3. Winding & air gap

V.BALAJI AP/EEE DCE

Mechanical design:

Rotating

Stationary

Frame Shaft bearings

Tank (Transformer tank)

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

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

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 φp Bav = π DL

Specific electrical loading (ac) IzZ ac = πD

Similarities in Electric & Magnetic circuits. S.N Electric Circuits o 1. The emf circulates Current in a closed path.

Magnetic Circuits The mmf creates flux in a closed path.

2.

Flow of current is opposed by resistance of the circuit.

The creation of flux is opposed by reluctance of the ckt.

3.

The path of Current is called The path of flux is electric ckt. called magnetic ckt V.BALAJI, B.E. M.Tech, (Ph.D), MIEEE, MISTE, MIAENG.

Contd…. S.N Electric Circuits o

Magnetic Circuits

4.

Current = EMF/ Resistance Flux = mmf / Relutance

5.

Current density = current/area

Flux density = Flux/ area

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

Differences between Electric and Magnetic Circuits S. Electric Circuits No 1. Current actually flows in the electric ckt. 2.

3.

Magnetic Circuits

Flux does not flow, but it is only assumed to flow When current flows, the Energy is needed only energy is spent continuously. to create the flux but not to maintain it. Resistance is independent of Reluctance depends current strength. on total flux or flux density in the material. V.BALAJI, B.E. M.Tech, (Ph.D), MIEEE, MISTE, MIAENG.

Magnetic circuit:1. It provides path for flux lines 2. mmf creates flux against Reluctance calculate:- in smooth armature ys ws

Pole surface Closed slots Armature surface

Ws – width of slot Wt – width of tooth (i) For smooth armature closed type of slot are chosen V.BALAJI, B.E. M.Tech, (Ph.D), MIEEE, MISTE, MIAENG.

Reluctance in open type of slot:(without fringing flux ) ys flux liner lg

Ws

Wt

l s= µA lg sg = µ o Ag

l s= µA

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

Ag = L × wt

= L × ( ys − ws ) Sg =

Lg

µ o L ( y s − ws )

Semi closed type:-

ys

Fringing flux

ys’ lg

ws

wt

ws

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

Sg =

lg

µo Ag ′

Ag = ys × L

= L × w( ys − ws )

Sg =

lg

µo L( ys − wo )

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

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

fringing flux lg

ωs

ωt

Sg =

lg

ωs

µ o Ag

A g = y ′s × L y ′s = w t + δ w s y s = ws + wt ⇒ wt = y s − ws

y′s = ys −ωs + δωs y′s = ys −ωs (1−δ ) = ys − ws (kcs)

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:-

1 ksc (semi closed slots) = 1 + Slg / w Open slots:-

2  −1 1 2 kcs =  tan y − log 1 + y  π π  wo y= 2l g

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

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

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

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

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

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

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

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

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

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

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

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




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