502942 class 36 dc generator

8/14/2019 502942 Class 36 DC Generator

1/20

01/16/10

1

Welcome to

Lectures on D.C.Machine


2/20

01/16/10

2

D. C. Generator
http://upload.wikimedia.org/wikipedia/commons/a/a9/Prokudin-Gorskii-30.jpghttp://upload.wikimedia.org/wikipedia/commons/a/a9/Prokudin-Gorskii-30.jpghttp://upload.wikimedia.org/wikipedia/commons/a/a9/Prokudin-Gorskii-30.jpg


3/20

01/16/10

3

Portable D. C. Generator
http://upload.wikimedia.org/wikipedia/commons/7/7d/Portable_electrical_generator_angle.jpg


4/20

01/16/10

4

DIRECT CURRENT

MACHINESDC machine Construction

The major advantages of DCmachines are: easy speed andtorque regulation.

The stator of the DC motor haspoles, which are excited by DCcurrent to produce magnetic fields.

The rotor has a ring-shapedlaminated iron-core with slots.

Coils with several turns are placed inthe slots. The distance between thetwo legs of the coil is about 180electric degrees.

N S

Stator with

with polesBrush

Rotor

Field


5/20

01/16/10

5

D. C. Generator

Principle of Operation

When a conductor rotates in a magnetic field,

dynamically induced e.m.f is produced in it

according to Faradays law of electromagnetic

induction


6/20

01/16/10

6

Generated EMF

Let

Ei.epathsparalleltheofoneanyingeneratedEMFEEMFGenerated

ArmatureinpathparallelanyininducedEMFE

rpminrotationArmatureN

ArmatureinPathsParallelofNo.A

polesGeneratorofNo.P

SlotperConductorsofNo.SlotsofNo.

ConductorsArmatureofNo.TotalZ

WbinFlux/Pole

g =

====

===


7/20

01/16/10

7

secN

60dt,revolution1forTime

N/60s/secRevolutionofNo.

WbPd,revolution1intorcut/conducFluxNow,

voltdt

dConductorGenerated/EMFAverage

=

==

=

Hence, according to Faradays Laws of electromagnetic induction,

volt60

PN

60/N

P

volt

dt

dconductorGenerated/EMF

==

=


8/20

01/16/10

8

For Wave wound Generator

No. of Parallel Paths = 2

No. of Conductors (in series) in 1 path = Z/2

volt

120

ZPNvolt

260

PNpathGenerated/EMF ==

Z


9/20

01/16/10

9

For Lap wound Generator

No. of Parallel Paths = P

No. of Conductors (in series) in 1 path = Z/P

volt60

ZNvolt

P60

PNpathGenerated/EMF ==

Z


10/20

01/16/10

10

In General,

Generated EMF

windinglapforP

windingwavefor2Awhere,

volt

A

P

60

ZNEg

==

=


11/20

01/16/10

11

Also,

voltA

P

Z

voltA

P

Z

N

Eg

=

= 2602

2

1

For a given D.C. Machine, Z, P and A are constants

Hence, Putting

rps)inis(N

voltsNk2kE

get,we,A

ZPk

aag

a

==

=


12/20

01/16/10

12

Types of D.C. Generators

According to the way in which their fieldsare excited, generators are classified into :

i) Separately excited D.C. Generator

ii) Self- excited D.C. Generator


13/20

01/16/10

13

Separately excited D.C. Generators are those whose field

magnets are energized from an independent source of D.C. Current

Eg

L

O

A

D

+

-

I

Field Winding

R

Brush

Brush

V

If

DropsBrushIREV ag =Ra = Armature Resistance


14/20

01/16/10

14

Self excited D.C. Generators are those whose field

magnets are energized by the currents produced by the generators

themselves.

ere are 3 types of self-excited D.C. Generators named according to

e manner in which their field coils are connected to the armature.

ese are :

Shunt wound D.C. Generator

Series wound D.C. Generator

Compound wound D.C. Generator


15/20

01/16/10

15

i) Shunt wound D.C. Generator

Eg

LOAD

+

-

I

Shunt Field V

Ia

Ish

Rsh

Ra

Rsh Shunt Field Resistance

Ra - Armature Resistance

sha III +=DropsBrushRIEV aag =

shshRIV =


16/20

01/16/10

16

Eg

L

O

A

D

+

Ia=Ise=I

Se ries Field

V

Rse

ii) Series wound D.C. Generator

DropsBrush)RR(IEV seaag +=


17/20

01/16/10

17

iii) Compound wound D.C. Generator

Eg

L

OA

D

I

Shunt Field

V

Ia

Ish

Series Field

Short Shunt


18/20

01/16/10

18

Eg

L

O

AD

I

Shunt FieldV

Ia

Ish

Series Field

Long Shunt


19/20

01/16/10

19

Ex.1 A D.C. Shunt Generator delivers 450A at 230V and the

resistance of the shunt field and armature are 50 and 0.03

respectively. Calculate the generated EMF.


20/20

01/16/10

20

Ex.2 An 8 - pole D.C. Shunt Generator with 778 wave

wound armature conductors running at 500 rpm supplies

a load of 12.5 resistance at terminal voltage of 250V.

The armature resistance is 0.24 and the field resistance is 250 .

Find the armature current, the generated EMF and the flux per pole.

502942 class 36 dc generator

Documents