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Spring 2002 ELCT 553 Synchronous generator:

Operation

1

Synchronous Generators:Operation

We consider:isolated generator

generator connected in parallelwith a large system

two generators connected inparallel

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Spring 2002 ELCT 553 Synchronous generator:

Operation

2

Isolated generator

Control prime mover throttle

to control speedspeed governor measures

speed and uses a control loopto regulate it to generate 60 Hz(for example)

average load power met (up tothe system limits)

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Spring 2002 ELCT 553 Synchronous generator:

Operation

3

Control exciter to controlterminal voltage

voltage regulator measuresarmature voltage and uses a

control loop to regulate it togenerate at rated voltage

the reactive power needs of theload are met (up to systemlimits)

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Spring 2002 ELCT 553 Synchronous generator:

Operation

4

VAjXS IA Load

EA

IA

VA

EA

jXSIA

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Spring 2002 ELCT 553 Synchronous generator:

Operation

5

EA

IA

XSIA

VAdq g

EAsin(d)=XSIAcos(q)

q

EAcos(d)-VA=XSIAsin(q)

S

AAA

S

AA

X

)V-)cos((E3VAA

X

)sin(E3V

AA

)sin(IV3Q

)cos(I3VP

d

d

=q=

=q=

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Spring 2002 ELCT 553 Synchronous generator:

Operation

6

Since the speed and |VA| areregulated:

Load average power (P) increasescause increased values ofd(caused by increased powerinput)

Load reactive power (Q) increases

cause |EA| to increase (byincreased field current)

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Spring 2002 ELCT 553 Synchronous generator:

Operation

7

EA

IA

XSIA

VA

d

q

g

Increase P at constant Q

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Spring 2002 ELCT 553 Synchronous generator:

Operation

8

EA

IA

XSIA

VA

dq

g

Increase Q at constant P

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Spring 2002 ELCT 553 Synchronous generator:

Operation

9

EA

IA

XSIA

VAdq g

Increase |S| at constant pf

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Spring 2002 ELCT 553 Synchronous generator:

Operation

10

Generator in parallel with alarge system

Infinite bus = generator withinfinite inertia and zero internal

reactance = ideal ac voltagesource

approximate representation of alarge power system

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Spring 2002 ELCT 553 Synchronous generator:

Operation

11

Governor characteristicf

[Hz]

fnl

sp=-DP/Df

P

[kW]

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Spring 2002 ELCT 553 Synchronous generator:

Operation

12

genbusf[Hz]

load

fnl

PB [kW] PB1 PG1 PG [kW]Pload

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Spring 2002 ELCT 553 Synchronous generator:

Operation

13

f

[Hz]

fnl

PG2PB2

Pload

PG1

Raise

Pload

PB1PB [kW] PG [kW]

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Spring 2002 ELCT 553 Synchronous generator:

Operation

14

Two generators in parallel

f [Hz]

f

P2

Pload

P1P1 [kW] P2 [kW]

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Spring 2002 ELCT 553 Synchronous generator:

Operation

15

Same load, raise unit 2, f increases,

load shifts from 1 to 2

f [Hz]

f

P2

Raise

Pload

P1P1 [kW] P2 [kW]

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Spring 2002 ELCT 553 Synchronous generator:

Operation

16

Excitation system

characteristicVT [kV]

Vnl

sq=-DQ/DV

Q

[kVAr]