Chapter 5 EE 342 Syn Gen

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Electric generator family tree

ElectricGenerator


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Synchronous Generators(Rotor speed )n m= n syn =120 f/P

Chapter No : 5 Page 250

f =n mP/120

Synchronous generator is the most importantcomponent in the power system

Source of 99% of the MW in most power systems


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http://www.wvic.com/how-gen-works.htm


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http://www.wvic.com/how-gen-works.htmhttp://www.wvic.com/how-gen-works.htm


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http://upload.wikimedia.org/wikipedia/commons/7/7d/Portable_electrical_generator_angle.jpg


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Synchronous Machines

Generator

Exciter

View of a two-pole round rotor generator and exciter.


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Generation Operation


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http://en.wikipedia.org/wiki/File:3-phase_flow.gif


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A i fi ld i id d b h DC i fi ld i di


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A magnetic field is provided by the DC-current carrying field winding which induces the desired AC voltage in the armature winding

Field winding is always located on the rotor where it is connected to anexternal DC source via slip rings and brushes or to a revolving DC

source via a special brushless configuration Armature winding is located on the stator where there is no rotation

The armature consists of three windings all of which are wound on thestator, physically displaced from each other by 120 degrees


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The generator is classified as a synchronousmachine because it is only at synchronousspeed that it can develop electromagnetictorque

= frequency in rad/sec

= machine speed in RPM p = number of poles on the rotor of the

machine

m e p2

e f 2

N p

f s 120


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No. of Poles (p) Synchronous speed (Ns)------------------- -----------------------------

2 36004 1800

6 12008 900

10 72012 600

14 51416 45018 40020 360

For 60 Hz operation (f=60) N p

f s120


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Two-pole salient pole generator concept.

B -

B+

A+

C+

C -

A-

Rotor withdc winding

Stator withlaminated iron core

N

SSlots with

phasewinding

+++++

-----


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Four-pole salient pole generator concept.

B -

B +

A +

C +C -

A -

-- +

+

- -

+ +- -

+ +

--+

+

N

SS

N

A +

C -

B +A -

B -

C +


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2 and 4 -pole machines have nonsalient (cylindrical) poles while machines with 4 or more poles have salient (sticking out) poles.


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Salient (sticking out) poles


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For 60 Hz operation (f=60)

Synchronous generator

Rotor construction

Round Rotor Salient Pole

Two pole s = 3600 rpm

Four Poles = 1800 rpm

Eight Pole s= 900 rpm


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Synchronous Machines-Stator

Details of a generator stator.

Laminated ironcore with slots

Insulated copper bars are placed inthe slots to formthe three-phasewinding

Metal frame


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Salient Pole

ConstructionSmooth rotor

Construction

S ynchronous Machine


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S ynchronous Machine

Two Pole Cylindrical Rotor Machine Four Pole Salient Rotor Machine

FieldWinding

FieldWinding


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The stator is similar in construction to Induction motor

The rotor can be Salient or Non-Salient

Field excitation is provided on the rotor by either permanent or electromagnetswith number of poles equal to the poles of the rotating magnetic field causedby stator

The rotor gets locked to the RMF and rotates u n l ike i nduc t i on mo to r atsynch ro no u s s p eed under all load condition

All conventional power plants use synchronous generators for converting power to electrical form


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Fact: hydro turbines are slow speed,steam turbines are high speed.

Do hydro-turbine generators have few poles or many?

Do steam-turbine generators have few poles or many?

Fact: salient pole incurs significant mechanical stress at high speed.

Do steam-turbine generators have salient poles or smooth?

Fact: Salient pole rotors are cheaper to build than smooth.

Do hydro-turbine generators have salient poles or smooth?


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Rotor block of a large generator. (Courtesy Westinghouse)


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Large generator rotor completely assembled. (Courtesy Westinghouse)

DC current terminals

Shaft

Steelretaining

ring

DC currentterminals

Wedges

Shaft


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Figure 6.9Stator of a large salient pole hydro generator; insetshows the insulated conductors and spacers.


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Figure 6.10 Large hydro generator rotor with view of the vertical poles.


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Figure 6.11 Rotor of a four-pole salient pole generator.

Pole

DC excitationwinding

Fan

Sliprings


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shows the rotor and stator of a hydrogenerator, which uses asalient pole rotor.


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Fig 5-3 (Page 253) Brushless exciter


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ROTOR

STATOR

Synchronous Machine Main Field

Three-Phase output

Red

Yellow

Blue

Main Armature

Pole

DC excitationwinding

Fan

Sliprings

Fig 5 3 (Page 253) Brushless exciter


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http://en.wikipedia.org/wiki/File:3-phase_flow.gifhttp://commons.wikimedia.org/wiki/File:Simpel-3-faset-generator.gif


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http://en.wikipedia.org/wiki/File:Induction-motor-3a.gif


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Three-phase induction motors

Animation of a squirrel-cage AC motor

http://www.coolmagnetman.com/magacmot.htm
http://en.wikipedia.org/wiki/File:Induction-motor-3a.gif


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http://www.zeva.com.au/tech.php?section=motors

Permanent Magnet DC Motor DC Motor with wound stator

Brushless DC Motor ("in-runner" type) AC Induction Motor


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Chapter 5 EE 342 Syn Gen