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Mesin Sinkron


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Synchronous Machines

• Synchronous generators or alternators are used to convert

mechanical power derived from steam, gas, or hydraulic-turbine

to ac electric power

• Synchronous generators are the primary source of electrical

energy we consume today

• Large ac power networks rely almost exclusively on synchronous

generators

•Synchronous motors are built in large units compare to inductionmotors (Induction motors are cheaper for smaller ratings) and

used for constant speed industrial drives


3/49

Construction

Basic parts of a synchronous generator:

• Rotor – belitan medan (dc excited winding

• Stator – belitan armatur (!"phase winding in which the

ac emf is generated

#he manner in which the acti$e parts of a synchronous

machine are cooled determines its o$erall physical si%e and

structure


4/49

&arious #ypes

Mesin sinkron dengan rotor kutub menon'ol

(Salient"pole synchronous machine

Mesin sinkron dengan rotor silindris (Cylindrical

or round"rotor synchronous machine


5/49

) Most hydraulic turbines ha$e to turn at low speeds

(between *+ and !++ r,min-) . large number of poles are re/uired on the rotor

0ydrogenerator

urbine

0ydro (water

1 ≈ + m

2on"uniform

air"gap !

S S

!

d"axis

/"axis

Salient"3ole Synchronous 4enerator


6/49

Salient"3ole Synchronous 4enerator

Stator

S a l i e n t - p o l e r o t o

r


7/49

5≈

+ m

1 ≈ m#urbine

Steam

Stator

"niform air-gap

Stator winding

#otor

#otor winding

!

S

$igh speed

%&'' rmin ⇒

2-pole

*'' rmin ⇒

4-pole

î +irect-conductor cooling (using hydrogenor water as coolant)

î #ating up to ''' ./

#urbogenerator

d"axis

/"axis

Cylindrical"Rotor Synchronous 4enerator


8/49

Cylindrical"Rotor Synchronous 4enerator

Stator

Cylindrical rotor


9/49

6peration 3rinciple

#he rotor of the generator is dri$en by a prime"mo$er

. dc current is flowing in the rotor winding which

produces a rotating magnetic field within the machine

#he rotating magnetic field induces a three"phase$oltage in the stator winding of the generator


10/49

7lectrical 8re/uency

7lectrical fre/uency produced is locked or synchroni%ed tothe mechanical speed of rotation of a synchronous

generator:

where f e 9 electrical fre/uency in 0%

P 9 number of polesnm9 mechanical speed of the rotor in r,min

)'

m

e

n P

f =


11/49

4enerated &oltage

#he generated $oltage of a synchronous generator is gi$en by

where 9 flux in the machine (function of I f

nm 9 electrical fre/uency

K c= synchronous machine constant

Saturation characteristic of a synchronous generator)

mc n K E φ =

I f

E


12/49

&oltage Regulation

/ convenient way to compare the voltage behaviour of two

generators is by their voltage regulation (VR)0 he VR of asynchronous generator at a given load, power factor, and at rated

speed is defined as

%V

V E

VR fl

fl nl

)''

1here V fl is the full-load terminal voltage, and E

nl (e2ual to E

f )

is the no-load terminal voltage (internal voltage) at rated speed

when the load is removed without changing the field current0

3or lagging power factor ( PF ), VR is fairly positive, for unity

PF , VR is small positive and for leading PF , VR is negative0


13/49

7/ui$alent Circuit;

o he internal voltage E f produced in a machine is not usually the

voltage that appears at the terminals of the generator0

o he only time E f is same as the output voltage of a phase is

when there is no armature current flowing in the machine0

o here are a number of factors that cause the difference between

E f and V t 4

– he distortion of the air-gap magnetic field by the current flowing

in the stator, called the armature reaction

– he self-inductance of the armature coils0

– he resistance of the armature coils0

– he effect of salient-pole rotor shapes0


14/49

generator

motor

I a

I a

E f E res V t

jX jX l Ra

55

5

7/ui$alent Circuit;-

62uivalent circuit of a cylindrical-rotor synchronous machine


15/49

3hasor 1iagram

φ r

φ f

φ a r

Ia

E f

E re s j Ia X s

V t Ia Ra

j Ia X l

j Ia X δ

δ

φ

7hasor diagram of a cylindrical-rotor synchronous generator,for the case of lagging power factor

Lagging 734 8V t 898 E f 8 for overexcited condition

Leading 734 8V t 8:8 E f 8 for underexcited condition


16/49

3hasor 1iagram

he synchronous impedance of a %0 k./, ;;'-., delta

connected , %-phase, synchronous generator is 5


17/49

#hree"phase e/ui$alent circuit of a cylindrical"rotor

synchronous machine

he voltages and currents of the three phases are 'o apart in angle,

but otherwise the three phases are identical0

5

I a1

E f1 jX s Ra5

I a 2

E f 2

j X s

R a

5

I a 3

E f 3

j X s

R a

5

V !

V ! "s#rt$3%V t

V t


18/49

1etermination of the parameters of the e/ui$alent

circuit from test data

•he e2uivalent circuit of a synchronous generator that has beenderived contains three 2uantities that must be determined in order

to completely describe the behaviour of a real synchronous

generator4

– he saturation characteristic4 relationship between I f and φ (and

therefore between I f and E f )

– he synchronous reactance, X s

– he armature resistance, Ra•

•he above three 2uantities could be determined by performing thefollowing three tests4

– >pen-circuit test

– Short-circuit test

– += test


19/49

6pen"circuit test • he generator is turned at the rated speed

•he terminals are disconnected from all loads, and the field currentis set to ?ero0

• hen the field current is gradually increased in steps, and the

terminal voltage is measured at each step along the way0

• It is thus possible to obtain an open-circuit characteristic of a

generator ( E f or V t versus I f ) from this information

+

.dc

If

.t


20/49

Short"circuit test

•/d


21/49

– then

– If the stator is @-connected, the per phase stator resistance is

– If the stator is delta-connected, the per phase stator resistance is

1C #est

– he purpose of the += test is to determine Ra0 / variable += voltage

source is connected between two stator terminals0 – he += source is ad


22/49

1etermination of X s

• 3or a particular field current I f(, the internal voltage E f (AV () could

be found from the occ and the short-circuit current flow I sc)( could befound from the scc0

• hen the synchronous reactance X s could be obtained using

I f(

E f or V t (.)/ir-gap line

>== I sc (/)

S==

I f (/)

V rate*

V ( I sc)+

I sc) (

I f+

( )

sc(

f (

unsat ) saunsat ) s

I

E V X R ,

==+=

aunsat ) sunsat ) s R , X −=

sc(

oc )t

sc(

f

unsat ) s I

V

I

E X =≈

4 Ra is known from the += test0

Since X s)unsat :: Ra,


23/49

X s under saturated condition

I a

E f V

t A'

jX s Ra

55

E f V t A'

jI a X

s

I a R

a

I a

( )

sc+

f rate*

sat ) sa sat ) s I

E V X R ,

==+=

/t V

A

V rate*

,

a sat ) s sat ) s R , X −=4 R

a

is known from the += test0

7/ui$alent circuit and phasor diagram under condition

I f(

E f or V t (.)/ir-gap line

>== I sc (/)

S==

I f (/)

V rate*

V ( I sc)+

I sc) (

I f+


24/49

Short"circuit Ratio

/nother parameter used to describe synchronous generators is the

short-circuit ratio (S'R)0 he S=# of a generator defined as theratio of the fiel* current re#uire* for the rate* voltage at o-en

circuit to the fiel* current re#uire* for the rate* armature current

at short circuit 0 S'R is


25/49

7xample

/ '' k./, ;*'-., &'-$?, ;-pole, @-=onnected synchronousgenerator with a rated field current of B / was tested and the

following data was taken0

a) from >= test C terminal voltage A B;' . at rated field

current

b) from S= test C line current A %''/ at rated field currentc) from +c test C += voltage of ' . applied to two terminals,

a current of B / was measured0

0 =alculate the speed of rotation in rmin

0 =alculate the generated emf and saturated e2uivalent circuit parameters (resistansi belitan stator dan reaktansi sinkron)


26/49

Solution to 7xample 0

f e " electrical fre2uency " Pnm 0 '

f e " &'$?

P " number of poles " ;

nm " mechanical speed of rotation in rmin.

So, speed of rotation nm " ' f e 0 P

" (' x &'); " *'' rmin0 In open-circuit test, I a A ' and E f AV t

E f " B;'0D%

A %0* . (as the machine is @-connected)

In short-circuit test, terminals are shorted, V t A '

E f " I a , s or , s A E f 0I a A%0*%''A0'; ohm

3rom the += test, Ra"V &' 0 ( I &' )A '(EB) A '0 ohm

Synchronous reactance,

, sat sa sat s X R , +=

'0)0'';0)

,, =−=−= a sat s sat s R , X

I a

E f

V t

j0' '0

5

5


27/49

3roblem

/ ;*'-., &'-$?, @-=onnected synchronous generator, having the

synchronous reactance of 0'; ohm and negligible armatureresistance, is operating alone0 he terminal voltage at rated field

current at open circuit condition is ;*'.0

0 =alculate the voltage regulation

0 If load current is ''/ at '0* 73 lagging

0 If load current is ''/ at '0* 73 leading

%0 If load current is ''/ at unity 73

(gambarkan terlebih dahulu diagram fasornya)

0 =alculate the real and reactive power delivered in each case0%0 State and explain whether the voltage regulation will

improve or not if the load current is decreased to B' / from

'' / at '0* 73 lagging0


28/49

Problem 2

/ ;*' ., &' $?, +elta-connected, four pole synchronous generator has the>== shown below0 his generator has a synchronous reactance of '0 ohm

and armature resistance of '0'B ohm0 /t full load, the machine supplies'' / and '0* pf lagging0 "nder full-load conditions, the friction andwindage losses are ;' k1, and the core losses are %' k10 Ignore field circuitlosses0

a) 1hat is the speed of rotation of the generatorF

b) $ow much field current must be supplied to the generator to make theterminal voltage ;*' . at no loadF

c) If the generator is now connected to a load and the load draws '' / at '0* pf lagging, how much field current will be re2uired to keep the terminalvoltage e2ual to ;*' .F

d) $ow much power is the generator now supplyingF $ow much power is

supplied to the generator by the prime-moverF1hat is the machineGs overall efficiencyF

e) If the generatorGs load were suddenly disconnectedfrom the line, what would happen to its terminal voltageF


29/49

Example 5-2 (pp291)


30/49

3arallel operation of synchronous generators

here are several ma


31/49

Hefore connecting a generator in parallel with another

generator, it must be synchroni?ed0 / generator is said to be

synchroni?ed when it meets all the following conditions4

• he rms line voltages of the two generators must be

e2ual0

• he two generators must have the same -hase se#uence0

• he -hase angles of the two a phases must be e2ual0

• he oncoming generator fre#uency is e2ual to the

running system fre2uency0

Synchroni%ation

Load

enerator

enerator

Switch

a

c

a 0

0

c 0

S h i ti


32/49

Synchroni%ation

Loadenerator

#est of the

power system

enerator

X s1 E f1

X s2 E f2

X sn E fn

Infinite bus

V , f are constant

X s e# A '


33/49

Concept of the infinite bus

1hen a synchronous generator is connected to a power system,

the power system is often so large that nothing the operator of the

generator does will have much of an effect on the power system0

/n example of this situation is the connection of a single

generator to the =anadian power grid0 >ur =anadian power gridis so large that no reasonable action on the part of one generator

can cause an observable change in overall grid fre2uency0 his

idea is ideali?ed in the concept of an infinite bus0 (n infinite us

is a -oer system so large that its voltage an* fre#uency *o not

vary regar*less of ho much real or reactive -oer is *ran from or su--lie* to it.


34/49

.cti$e and reacti$e power"angle characteristics

• P :'4 generator operation

• P 9'4 motor operation

•

7ositive 4 delivering inductive vars for a generator action orreceiving inductive vars for a motor action

• !egaive 4 delivering capacitive vars for a generator action or

receiving capacitive vars for a motor action

P m P e, e

V t

3ig0 Synchronous generator connected to an infinite bus0


35/49


• he real and reactive power delivered by a synchronous

generator or consumed by a synchronous motor can be

expressed in terms of the terminal voltage V t , generated voltage

E f , synchronous impedance , s, and the power angle or tor2ueangle δ0

• #eferring to 3ig0 *, it is convenient to adopt a convention that

makes positive real power 7 and positive reactive power J

delivered by an overe4cite* generator 0

• he generator action corresponds to positive value of δ, whilethe motor action corresponds to negative value of δ0

P m P

e

, e

V t


36/49

he complex power output of the generator in volt-amperes per phase is given by

Kat

L

I.


37/49


P m P e, e

V t

and the armature current,

( ) s

f t f

s

t

/

f

/

a

/

jX

sin jE V cos E

jX

V E I δ+−δ=−=

where X s is the synchronous reactance per phase0

( )

s

t f t

s

f t

s

t f t

s

f t

s

f t f t

5a

/ t

/

X

V cos E V 3

6 X

sin E V P

X

V cos E V j

X

sin E V

jX sin jE V cos E V I V j3 P S

−δ=

δ=∴

−δ+

δ=

−δ−−δ==+=


38/49


P m P e, e

V t

s

t f t

s

f t

X

V cos E V 36

X

sin E V P

−δ=

δ=∴

• he above two e2uations for active and reactive powers holdgood for cylindrical-rotor synchronous machines for negligibleresistance

• o obtain the total power for a three-phase generator, the abovee2uations should be multiplied by % when the voltages are line-to-neutral

• If the line-to-line magnitudes are used for the voltages, however,these e2uations give the total three-phase power


39/49

Steady"state power"angle or tor/ue"angle characteristic of a

cylindrical"rotor synchronous machine (with negligible

armature resistance)

+δ

#eal power or tor2ue

generator

motor

+π+π/2

−π/2

0

−π

7ull-out tor2ue

as a generator

7ull-out tor2ue

as a motor

−δ

Steady state stability limit


40/49

Steady"state stability limit

otal three-phase power4 δ= sin X

E V P

s

f t %

he above e2uation shows that the power produced by a synchronousgenerator depends on the angle δ between the V

t and E

f 0 he maximum

power that the generator can supply occurs when δAM'o0

s

f t

X

E V P

%=

he maximum power indicated by this e2uation is called stea*y!state

staility limit of the generator0 If we try to exceed this limit (such as by

admitting more steam to the turbine), the rotor will accelerate and lose

synchronism with the infinite bus0 In practice, this condition is never reached

because the circuit breakers trip as soon as synchronism is lost0 1e have to

resynchroni?e the generator before it can again pick up the load0 !ormally,

real generators never even come close to the limit0 3ull-load tor2ue angle of

Bo to 'o are more typical of real machines0


41/49

3ull"out tor/ue

he maximum tor2ue or -ull!out tor#ue per phase that a two-pole

round-rotor synchronous motor can develop is

π

=ω

=

&' s

ma4

m

ma4

ma4n

P P 7

where n s is the synchronous speed of the motor in rpm

P

δ

P or

3ig0 /ctive and reactive power as a function of the internal angle


42/49

3roblem -

/ '*-., ;B-k./, '0*-73 leading, -connected, &'-$?

synchronous machine having 0'; ohm synchronous

reactance and negligible armature resistance is supplying a

load of k1 at '0* power factor leading0 3ind the armature

current and generated voltage and power factor if the load isincreased to ' N10 !eglect all other losses0


43/49

Synchronous Motors

• / synchronous motor is the same physical machine as agenerator, except that the direction of real power flow isreversed

•

Synchronous motors are used to convert electric power tomechanical power

• ost synchronous motors are rated between B' k1 (''hp) and B 1 (',''' hp) and turn at speed ranging fromB' to *'' rmin0 =onse2uently, these machines are used in

heavy industry• /t the other end of the power spectrum, we find tiny single-

phase synchronous motors used in control devices andelectric clocks

P ,

V t

otor


44/49

6peration 3rinciple

• he field current of a synchronous motor produces a steady-

state magnetic field + R• / three-phase set of voltages is applied to the stator windings of

the motor, which produces a three-phase current flow in the

windings0 his three-phase set of currents in the armature

winding produces a uniform rotating magnetic field of + s• herefore, there are two magnetic fields present in the machine,

and the rotor fiel* ill ten* to line u- ith the stator fiel* ,


45/49

&ector 1iagram

• he e2uivalent circuit of a synchronous motor is exactly same asthe e2uivalent circuit of a synchronous generator, except that the

reference direction of I a is reversed0

• he basic difference between motor and generator operation in

synchronous machines can be seen either in the magnetic fielddiagram or in the phasor diagram0

• In a generator, E f lies ahead of V t , and + R lies ahead of +net 0 In a

motor, E f lies behind V t , and + R lies behind +net 0

• In a motor the induced tor2ue is in the direction of motion, and in a

generator the induced tor2ue is a countertor2ue opposing the

direction of motion


46/49

&ector 1iagram

θ δ

I a

V t

E f

jI a X

s

θ

δ

I a

V t

E f

jI a X s

δ

+ s

+net

+ R

ω sync

3ig0 he phasor diagram (leading 734 overexcited and 8V t 898 E f 8) andthe corresponding magnetic field diagram of a synchronous motor0

3ig0 he phasor diagram of an underexcited synchronous

motor (lagging 73 and 8V t 8:8 E

f 8)0


47/49

.pplication of Synchronous Motors

Synchronous motors are usually used in large si?es because in small si?es

they are costlier as compared with induction machines0 he principaladvantages of using synchronous machine are as follows4

– 7ower factor of synchronous machine can be controlled very easily

by controlling the field current0

–

It has very high operating efficiency and constant speed0 – 3or operating speed less than about B'' rpm and for high-power

re2uirements (above &''N1) synchronous motor is cheaper than

induction motor0

In view of these advantages, synchronous motors are preferred for

driving the loads re2uiring high power at low speedO e0gO reciprocating pumps and compressor, crushers, rolling mills, pulp grinders etc0


48/49

3roblem *"-- (pp)!

Sebuah generator sinkron dengan data-data nameplate ''-./, 0B-k., '0*B 73 lagging, B' $?, -kutub, hubungan @,

mempunyai reaktansi sinkron , pu dan resistansi armatur

',' pu0

a) entukan nilai reaktansi sinkron dan resistansi armatur dalamsatuan ohm0

b) entukan besar tegangan induksi pada belitan stator ( E f ) pada

kondisi-kondisi nominal diatas0 entukan


49/49

3roblem *"-! (pp)!

/ three-phase, @-connected synchronous generator is

rated ' ./, %0 k., '0* power lagging, and &' $?0Its synchronous reactance is '0M ohm and its armature

resistance may be ignored0

a) 1hat is its voltage regulation at rated loadF b) 1hat would the voltage and apparent power rating of this

generator be if it were operated at B' $? with the same

armature and field losses as it had at &' $?F

c) 1hat would the voltage regulation of the generator be atB' $?F

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