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8/17/2019 Prinsip Kerja Mesin Sinkron
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Mesin Sinkron
8/17/2019 Prinsip Kerja 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
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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
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&arious #ypes
Mesin sinkron dengan rotor kutub menon'ol
(Salient"pole synchronous machine
Mesin sinkron dengan rotor silindris (Cylindrical
or round"rotor synchronous machine
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) 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
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Salient"3ole Synchronous 4enerator
Stator
S a l i e n t - p o l e r o t o
r
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5≈
+ m
1 ≈ m#urbine
Steam
Stator
"niform air-gap
Stator winding
#otor
#otor winding
!
S
$igh speed
%&'' rmin ⇒
2-pole
*'' rmin ⇒
4-pole
î +irect-conductor cooling (using hydrogenor water as coolant)
î #ating up to ''' ./
#urbogenerator
d"axis
/"axis
Cylindrical"Rotor Synchronous 4enerator
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Cylindrical"Rotor Synchronous 4enerator
Stator
Cylindrical rotor
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6peration 3rinciple
#he rotor of the generator is dri$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
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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 =
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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
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&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
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7/ui$alent Circuit;
o he internal voltage E f produced in a machine is not usually the
voltage that appears at the terminals of the generator0
o he only time E f is same as the output voltage of a phase is
when there is no armature current flowing in the machine0
o here are a number of factors that cause the difference between
E f and V t 4
– he distortion of the air-gap magnetic field by the current flowing
in the stator, called the armature reaction
– he self-inductance of the armature coils0
– he resistance of the armature coils0
– he effect of salient-pole rotor shapes0
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generator
motor
I a
I a
E f E res V t
jX jX l Ra
55
5
7/ui$alent Circuit;-
62uivalent circuit of a cylindrical-rotor synchronous machine
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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
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3hasor 1iagram
he synchronous impedance of a %0 k./, ;;'-., delta
connected , %-phase, synchronous generator is 5
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#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$3%V t
V t
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1etermination of the parameters of the e/ui$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
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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
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Short"circuit test
•/d
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– 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
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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,
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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$alent circuit and phasor diagram under condition
I f(
E f or V t (.)/ir-gap line
>== I sc (/)
S==
I f (/)
V rate*
V ( I sc)+
I sc) (
I f+
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Short"circuit Ratio
/nother parameter used to describe synchronous generators is the
short-circuit ratio (S'R)0 he S=# of a generator defined as theratio of the fiel* current re#uire* for the rate* voltage at o-en
circuit to the fiel* current re#uire* for the rate* armature current
at short circuit 0 S'R is
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7xample
/ '' k./, ;*'-., &'-$?, ;-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)
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Solution to 7xample 0
f e " electrical fre2uency " Pnm 0 '
f e " &'$?
P " number of poles " ;
nm " mechanical speed of rotation in rmin.
So, speed of rotation nm " ' f e 0 P
" (' x &'); " *'' rmin0 In open-circuit test, I a A ' and E f AV t
E f " B;'0D%
A %0* . (as the machine is @-connected)
In short-circuit test, terminals are shorted, V t A '
E f " I a , s or , s A E f 0I a A%0*%''A0'; ohm
3rom the += test, Ra"V &' 0 ( I &' )A '(EB) A '0 ohm
Synchronous reactance,
, sat sa sat s X R , +=
'0)0'';0)
,, =−=−= a sat s sat s R , X
I a
E f
V t
j0' '0
5
5
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3roblem
/ ;*'-., &'-$?, @-=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
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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 $ow much power is
supplied to the generator by the prime-moverF1hat is the machineGs overall efficiencyF
e) If the generatorGs load were suddenly disconnectedfrom the line, what would happen to its terminal voltageF
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Example 5-2 (pp291)
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3arallel operation of synchronous generators
here are several ma
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Hefore connecting a generator in parallel with another
generator, it must be synchroni?ed0 / generator is said to be
synchroni?ed when it meets all the following conditions4
• he rms line voltages of the two generators must be
e2ual0
• he two generators must have the same -hase se#uence0
• he -hase angles of the two a phases must be e2ual0
• he oncoming generator fre#uency is e2ual to the
running system fre2uency0
Synchroni%ation
Load
enerator
enerator
Switch
a
c
a 0
0
c 0
S h i ti
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Synchroni%ation
Loadenerator
#est of the
power system
enerator
X s1 E f1
X s2 E f2
X sn E fn
Infinite bus
V , f are constant
X s e# A '
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Concept of the infinite bus
1hen a synchronous generator is connected to a power system,
the power system is often so large that nothing the operator of the
generator does will have much of an effect on the power system0
/n example of this situation is the connection of a single
generator to the =anadian power grid0 >ur =anadian power gridis so large that no reasonable action on the part of one generator
can cause an observable change in overall grid fre2uency0 his
idea is ideali?ed in the concept of an infinite bus0 (n infinite us
is a -oer system so large that its voltage an* fre#uency *o not
vary regar*less of ho much real or reactive -oer is *ran from or su--lie* to it.
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.cti$e and reacti$e power"angle characteristics
• P :'4 generator operation
• P 9'4 motor operation
•
7ositive 4 delivering inductive vars for a generator action orreceiving inductive vars for a motor action
• !egaive 4 delivering capacitive vars for a generator action or
receiving capacitive vars for a motor action
P m P e, e
V t
3ig0 Synchronous generator connected to an infinite bus0
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.cti$e and reacti$e power"angle characteristics
• he real and reactive power delivered by a synchronous
generator or consumed by a synchronous motor can be
expressed in terms of the terminal voltage V t , generated voltage
E f , synchronous impedance , s, and the power angle or tor2ueangle δ0
• #eferring to 3ig0 *, it is convenient to adopt a convention that
makes positive real power 7 and positive reactive power J
delivered by an overe4cite* generator 0
• he generator action corresponds to positive value of δ, whilethe motor action corresponds to negative value of δ0
P m P
e
, e
V t
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he complex power output of the generator in volt-amperes per phase is given by
Kat
L
I.
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.cti$e and reacti$e power"angle characteristics
P m P e, e
V t
and the armature current,
( ) s
f t f
s
t
/
f
/
a
/
jX
sin jE V cos E
jX
V E I δ+−δ=−=
where X s is the synchronous reactance per phase0
( )
s
t f t
s
f t
s
t f t
s
f t
s
f t f t
5a
/ t
/
X
V cos E V 3
6 X
sin E V P
X
V cos E V j
X
sin E V
jX sin jE V cos E V I V j3 P S
−δ=
δ=∴
−δ+
δ=
−δ−−δ==+=
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.cti$e and reacti$e power"angle characteristics
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
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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
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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
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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
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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
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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
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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* ,
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&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
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&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
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.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
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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
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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