Bab 7 MOTOR AC SINKRON - Bab 7 Motor AC
Edit by: Ir. Harlianto Tanudjaja, M.Kom,MM.
MOTOR
LISTRIK
Motor Listrik merupakan sebuah perangkat elektromagnetik
yang mengubah energi listrik menjadi energi mekanik.
Energi mekanik ini digunakan untuk, misalnya, memutar
impeller pompa, fan atau blower, menggerakan kompresor,
mengangkat bahan, dll di industri dan digunakan juga pada
Tree
Sumber : Lessons In Electric Circuits Volume II – AC, Sixth Edition, last
HUKUM FISIKA The Motor
F = B
I L [Newtons] North pole
B = Density of the magnetic flux in Teslas I = Induced current in Amps
L L = Length of conductor in field in metres
F Force Example 1 B If a conductor of length 0.4m carrying a current of
I
10.6A is placed in a magnetic field with a flux density of 0.03T, determine the force experienced by this conductor in newtons.
South pole
F =
0.03 x 10.6 x0.4 = 0.1272 N
Tangan Kiri
Fleming’s Left Hand Rule North pole
Each digit of your hand must be at right angles to both of the other two thumb motion L se c ond finger
Force current f irst finger B field
I South pole If the current is reversed, the direction of motion will change
The Motor Effect
Each digit of your hand must be at right North pole angles to both of the other two se c ond finger
F current Force thu m b motion B
I f irst finger field
South pole If the current is reversed, the direction of motion will change
The Motor Effect
Each digit of your hand must be at right North pole angles to both of the other two se c ond
F finger current Force thu m b motion B
I f irst finger field
South pole If the field is reversed, the motion will be in the opposite direction
The Motor Effect
Each digit of your hand must be at right South pole angles to both of the other two se c ond field finger
F f irst finger current Force thu m b
B motion
I North pole If the field is reversed, the motion will be in the opposite direction
field is clockwise Current into page field is anticlockwise Current out of page
Using the following convention, we can show why Fleming’s left hand rule works
The Motor Effect
Field lines in the same direction cause repulsion, field lines in opposite directions
cause attractionForce
Force attraction repulsion repulsion attraction The Motor Effect
South Pole North Pole South Pole North Pole
AC Machines
1. Select the proper ac motor type for various applications.
2. State how torque varies with speed for various ac motors.
3. Compute electrical and mechanical quantities for ac motors.
4. Use motor nameplate data.
5. Understand the operation and characteristics of three-phase induction motors, three-phase synchronous machines, various types of single-phase ac motors, stepper motors, and brushless dc motors.
Klasifikasi Motor Listrik Berdasarkan
Pasokan Input, Konstruksi, dan Mekanisme
Operasi
Sumber : http://dunia-listrik.blogspot.com/
AC Motors
AC motors can be divided into two main forms: synchronous motors
induction motors
High-power versions of either type invariably operate from a three- phase supply , but single-phase
Perbedaan Motor Sinkron dan asinkron
(Induksi)Machine
Synchronous machines are ac machine that have a field circuit supplied by an external dc source.
DC field winding on the rotor ,
AC armature winding on the stator
Origin of name: syn = equal, chronos = time
Synchronous machines are called ‘synchronous’ because
their
mechanical shaft speed is directly
MOTOR AC - SINKRON
Motor sinkron adalah motor AC yang bekerja pada
kecepatan tetap pada sistem frekuensi tertentu. Motor
ini memerlukan arus searah (DC) untuk pembangkitan
daya dan memiliki torque awal yang rendah, dan oleh
karena itu motor sinkron cocok untuk penggunaan awal
dengan beban rendah , seperti kompresor udara ,
Prinsip Kerja Motor AC Sinkron
Pada motor sinkron, supply listrik bolak-balik (AC ) membangkitkan fluksi medan
putar stator (B ) dan suplai listrik searah (DC) membangkitkan medan rotor (B ).
s s
Rotor berputar karena terjadi interaksi tarik-menarik antara medan putar stator dan
medan rotor. Namun dikarenakan tidak adanya torka-start pada rotor, maka motor
sinkron membutuhkan prime-mover yang memutar rotor hingga kecepatan sinkron
agar terjadi coupling antara medan putar stator (B ) dan medan rotor (B ) s r Sebuah motor sinkron dapat dinyalakan oleh sebuah motor dc pada satusumbu.Ketika motor mencapai kecepatan sinkron, arus AC diberikan kepada belitan
stator. Motor dc saat ini berfungsi sebagai generator dc dan memberikan eksitasi
medan dc kepada rotor. Beban sekarang boleh diberikan kepada motor sinkron. Motor
sinkron seringkali dinyalakan dengan menggunakan belitan sangkar tupai (squirrel-
cage) yang dipasang di hadapan kutub rotor. Motor kemudian dinyalakan seperti
halnya motor induksi hingga mencapai –95% kecepatan sinkron, saat mana arus
searah diberikan, dan motor mencapai sinkronisasi. Torque yang diperlukan untuk
.
Seperti diketahui, rotor motor sinkron terkunci dengan medan putar dan
harus terus beroperasi pada kecepatan sinkron untuk semua keadaan
beban. Selama kondisi tanpa beban (no-load), garis tengah kutub medan
putar dan kutub medan dc berada dalam satu garis (gambar di bawah
bagian a).Seiring dengan pembebanan, ada pergeseran kutub rotor ke
belakang, relatif terhadap kutub stator (gambar bagian b). Tidak ada
perubahan kecepatan. Sudut antara kutub rotor dan stator disebut sudut
torque
sinkron
Motor sinkron adalah motor ac yang memiliki kecepatan konstan, namunkecepatan dapat diatur karena kecepatannya berbanding lurus dengan
frekuensi. Motor sinkron secara khusus sangat baik digunakan untuk
kecepatan rendah . Kelebihan dari motor sinkron ini antara lain, dapat
dioperasikan pada faktor daya lagging maupun leading, tidak ada slip yang
dapat mengakibatkan adanya rugi-rugi Sedangkan kelemahan dari motor
sinkron adalah tidak mempunyai torka mula daya sehingga motor ini memiliki
efisiensi tinggi. , sehingga untuk starting diperlukan cara-cara tertentu. Bila
metode starting telah dapat dikembangkan kemudian hari, maka motor ini
Prinsip kerja 3 Phasa
1. Bila sumber tegangan tiga phasa dipasang pada kumpara stator, maka pada kumparan stator akan timbul medan putar dengan kecepatan
ns = kecepatan sinkron f = frekuensi sumber p = jumlah kutup
P f n s
120 P f n s
120
2. Medan putar stator akan memotong konduktor yang terdapat pada sisi rotor, akibatnya pada kumparan rotor akan timbul tegangan induksi ( ggl ) sebesar
E = tegangan induksi ggl f = frekkuensi N = banyak lilitan Q = fluks
E fN s
4 ,
44
2 DC Machine & AC machine
DC motor - ends of the coil connect to a
mechanical rectifier called commutator to
'rectify' the emf produced.AC motor - No need rectification, so don’t
AC Motor
As in the case, a current is passed through the coil, generating a torque on the coil.
Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave.
Synchronous Machine
Construction
Energy is stored in the inductance
As the rotor moves, there is a change in the energy stored
Either energy is extracted from the magnetic field (and becomes mechanical energy – motor)
Or energy is stored in the magnetic field and eventually flows into the electrical circuit that powers the
Synchronous Machine
DC field windings are mounted on
the (rotating) rotor - which is thus a rotating electromagnet AC windings are mounted on the (stationary) stator resulting in three-phase AC stator voltages and currents
The main part in the synchronous
Synchronous Machine
Rotor
There are two types of rotors used in synchronous machines: cylindrical (or round) rotors and salient pole rotors.
Salient pole rotors are less expensive than round rotors.
Cylindrical ( round) rotor – low speed machines (hydro-turbines)
Salient-Pole rotor - high speed
machines (steam-turbines)
Synchronous Machine
Construction-Rotor
i) Cylindrical (or round) rotor
i) Salient-pole rotor
Salient-Pole Synchronous Generator
1. Most hydraulic turbines have to turn at low speeds
(between 50 and 300 r/min)N uniform air-gap
D » 10 m S S q-axis
Turbin N e
Hydro
(water)
Hydrogenerator
Salient-Pole Synchronous Generator Stator t-pole rotor
Cylindrical-Rotor Synchronous Generator
D » 1 m Turbine» 10 m L Steam d-axis
Stator winding
N High speed
Uniform air- gap Þ 2-pole 3600 r/min
Stato r 1800 r/min Þ 4-pole
Rotor winding q-axis
Direct-conductor cooling (using Roto hydrogen or water as coolant) r
Rating up to 2000 MVA S
Turbogenerator
Cylindrical-Rotor Synchronous Generator Stator
Synchronous Machine
Synchronous machine rotors are simply rotating
electromagnets built to have as many poles as are produced by the stator windings.
DC currents flowing in the field coils surrounding
each pole magnetize the rotor poles.
The magnetic field produced by the rotor poles locks in with a rotating stator field, so that the shaft and the stator field rotate in synchronism.
Salient poles are too weak mechanically and develop too much wind resistance and noise to be used in large, high-speed generators driven by steam or gas turbines. For these big machines, the rotor must be a solid, cylindrical steel forging to
Synchronous Machine
Axial slots are cut in the surface of the cylinder to accommodate the field windings.
Since the rotor poles have constant polarity they must be supplied with direct current.
This current may be provided by an external dc generator or by a rectifier. In this case the leads from the field winding are connected to insulated rings mounted concentrically on the shaft. Stationary contacts called brushes ride on these slip rings to carry current to the rotating field windings from the dc supply. The brushes are made of a carbon compound to provide a good contact with low mechanical friction. An external dc generator used to provide current is called an “exciter.
Synchronous Machine Stator
The stator of a synchronous machine carries the armature or load winding which is a three-phase winding.
The armature winding is formed by interconnecting various conductors in slots spread over the periphery of the machine’s
stator. Often, more than one independent
three phase winding is on the stator. An arrangement of a three-phase stator winding is shown in Figure below. Noticethat the windings of the three-phases are
Synchronous Machine – Stator construction
3 p has e AC Synchronous Motor Operation
ELO 2.6 – Describe how an AC synchronous motor is started and its operating characteristics.
- Synchronous motors are like induction motors in that they both have stator windings that produce rotating magnetic field
- Unlike an induction motor, an external DC source excites the synchronous motor rotor and therefore requires slip rings and brushes
Figure: AC Synchronous Motor AC Synchronous Motor Operation
- Synchronous motors use wound rotor, shown in figure
- Slip rings and brushes needed
- Rotor is much more expensive to manufacture than squirrel cage rotor associated with AC induction motors
Figure: Wound Rotor Operation
Starting a Synchronous Motor
- Not self-starting, torque only developed when running at synchronous speed
- Needs some type of device to bring rotor to synchronous speed
Two ways of starting a synchronous motor:
1. Use a separate DC motor
2. Embed squirrel-cage windings on the face of the rotor
- If starting a synchronous motor with a separate DC motor, both motors may share a common shaft
- Upon bringing DC motor to synchronous speed, stator windings receive AC current, DC motor then acts as a DC generator and supplies DC field excitation to rotor of synchronous motor
- Once operating at synchronous speed, synchronous motor is ready for load
AC Synchronous Motor
Starting a Synchronous Motor
- More commonly, a squirrel-cage winding is embedded in face of rotor poles to start motor
- Starts as an induction motor, speed increases to ≈95% of synchronous speed, then direct current is applied and motor begins to pull into synchronism
- Pull-in torque is term for torque required to pull motor into synchronism
- Because of more complex nature and higher manufacturing cost, designers rarely specify synchronous motors
- However, large industrial applications sometimes use synchronous motors:
- – to accommodate large loads
- – to improve power factor of transformers in large industrial applications
- – in applications where a constant speed is important
A. Synchronous motors are the most commonly used motors in large
industrial applications.B. Synchronous motors develop starting torque in the same manner as induction motors.
C. Synchronous motors are not often used due to their more complex nature and higher manufacturing costs.
D. Synchronous motors can continue to operate with more slip than
induction motors, thus producing more torque.Correct answer is C.
Synchronous Machine
Magnetomotive Forces (MMF’s) and Fluxes Due to Armature and Field Windings
Flux produced by a stator winding Two Cycles of MMF around the Stator
Phase AC Motor Knowledge Check
Select all of the statements about single-phase AC motors that are true.
A. The starting winding in a single-phase AC motor is always energized while the motor is running.
B. Single-phase AC motors have a starting winding that is out of
phase with the main winding.C. The resistance and reactance of the starting winding must be the same as the main winding.
D. Single-phase AC motors are used for small load applications.
Correct answers are B and D. Rotating the stator produces a net magnetic field
Sistem 3 Phase
Further Study - AC Motor Performance
Synchronous Wound induction Cage Induction
Speed Speed
Synchronous Generator
Equivalent circuit model – synchronous
generatorSynchronous Speed
2 P s
P
f n s120
Matematis Motor AC sinkron Slip dari motor AC dihitung dengan : Di mana :
N = Kecepatan putar, dalam r rpm S = Slip normal, 0 sampai 1.
Sebagai contoh, sebuah motor dengan empat kutub beroperasi pada 60 Hz bisa memiliki plat nama 1725 RPM pada beban penuh, sedangkan bila dihitung kecepatannya 1800 RPM.
Machine
The frequency of the induced voltage is related to the rotor speed by:
where P is the number of magnetic poles fe is the power line frequency.
Typical machines have two-poles, four- poles, and six-poles
Matematis Motor AC
sinkron
Motor ini berputar pada kecepatan sinkron, yang diberikan oleh
persamaan berikut :
Ns = 120 f / P
di mana : N = kecepatan serempak, dalam rpm sF = frekuensi daya AC p = jumlah kutup per lilitan phase
Slip and Slip Frequency
n n s m s m s n
s s s
slip
Effect of Rotor Inductance on Torque
c I c
R js L c c
If the generator operates at a terminal voltage V while
T Ia supplying a load corresponding to an armature current , then;
In an actual synchronous machine, the reactance is much greater than the armature resistance, in which case;
Among the steady-state characteristics of a synchronous generator, its voltage regulation and power-angle characteristics are the most important ones. As for transformers, the voltage regulation of a synchronous generator is defined at a given load as;
Penggunaan Motor AC sinkron
Motor ini memerlukan arus searah (DC) untuk pembangkitan daya dan memiliki torque awal yang rendah, dan oleh karena itu motor sinkron cocok untuk penggunaan awal dengan beban rendah, seperti kompresor udara, perubahan frekuensi dan generator motor.
Synchronous Generator Example 2
A three-phase, wye-connected 2500 kVA and 6.6 kV generator operates at full-load. The per- phase armature resistance R and the a
synchronous reactance, X , are (0.07+j10.4).
dCalculate the percent voltage regulation at (a)
0.8 power-factor lagging, and (b) 0.8 power-factor leading.
Proteksi Motor AC sinkron Ada banyak metode kendali motor AC (motor induksi, motor
sinkron) dengan kelebihan dan kekurangannya. Namun secara
umum metode ini dapat dikelompokkan sebagai berikut:1.Kendali Skalar (v/f Konstan)
2.Kendali Berorientasi Medan (Field Oriented Control, FOC)
3.Kendali Torsi Langsung (Direct Torque Control, DTC)
Proteksi Motor AC sinkron
Sesuai dengan namanya proteksi motor ini menggunakan panas sebagai
pembatas arus pada motor. Alat ini sangat banyak dipergunakan saat ini.
Biasanya disebut TOR, Thermis atau overload relay. Cara kerja alat ini adalah
dengan mengkonversi arus yang mengalir menjadi panas untuk
mempengaruhi bimetal.Bimetal inilah yang menggerakkan tuas untuk menghentikan aliran listrik
pada motor melalui suatu control motor starter. Pembatasan dilakukan dengan
mengatur besaran arus pada dial di alat tersebut. Jadi alat tersebut memiliki
range adjustment misal TOR dengan range 1 ~ 3,2 Amp disetting 2,5 Amp.
Artinya, kita membatasi arus dengan TOR pada level 2,5 Amp saja.
Proteksi Motor AC Sinkron
Overload Motor Protection, yang dimaksud motor ini adalah electric motor
yang oleh orang awam disebut dinamo. Dan disini dikhususkan yang terjadi pada
motor AC 3 phase. Fungsi dari motor ini adalah sebagai penggerak atau untuk
mengkonversi energi listrik menjadi mekanik / gerak seperti lift, conveyor, blower,
crusher dll.Dalam dunia industri saat ini peran yang dilakukan motor ini sangat vital.
Untuk itu proteksi sangat diperlukan untuk menjaga kelancaran suatu proses.
Sistem proteksi motor ini sudah lama dikenal dan berkembang seiring kemajuan
teknologi. Mulai dari penggunaan eutic relay, thermal, sampai elektronik. Secara
umum sistem kerja alat tersebut dapat dibagi menjadi dua yaitu dengan thermal
dan elektronik. THERMAL OVERLOADsinkron
Pembangkitan Torka
s rInteraksi antara medan putar stator (B ) dan medan rotor (B ) yang
- membangkitkan torka seperti terlihat dalam persamaan berikut :
T = B x B (sin δ)
s s δ disebut sudut beban karena besarnya tergantung pembebanan. Pada saatbeban nol nilai δ = 0. Jika dibebani, medan rotor tertinggal dari rotor sebesar δ,
okemudian berputar sama lagi. Beban maksimum tercapai pada δ = 90 . Jika
beban dinaikkan terus melebihi batas itu, maka motor akan kehilangan
sinkronisasi dan akhirnya akan berhenti.
sinkron
Pembangkitan Medan Putar
Pada Motor sinkron 3 fasa, mengalir arus seimbang pada tiap fasa dengan beda sudut
o fasa 120i = I sin ωt
a m oi = I sin (ωt-120 )
b m oi = I sin (ωt-240 )
c mTiap arus fasa membangkitkan ggm F yang merupakan fungsi sudut ruang seperti :
i à F .cos θ. Dengan F =F . sin ωt
a a a mMaka ggm F tiap fasa yang dibangkitkan :
F = F sin ωt.cos θ
a m o oF = F sin (ωt-120 ).cos (θ-120 )
b m o oF = F sin (ωt-240 ) .cos (θ-240 )
c mResultan ketiga ggm, F =F + F +F r a b c
Pengukuran Motor AC sinkron
Jika kemudian disederhanakan dengan persamaan trigonometri akan diperoleh:
F(θ,t) = 3/2 F .cos (θ-ωt)
m
Yang berarti resultan-mmf adalah medan putar sebagai fungsi dari ruang dan
waktu, seperti terlihat dalam gambar berikut :Karakteristik Motor AC sinkron
Gambar di atas memperlihatkan bahwa Torka (Torque) adalah fungsi sin δ,
dengan δ adalah sudut daya. Pada motor sinkron nilai δ negatif dan nilainya
opositif pada generator sinkron. Torka maksimum dicapai pada δ= +/- 90 . Jika
melebihi batas itu, maka motor atau generator akan kehilangan stabilitas dan
sinkronisasi sehingga pada akhirnya akan berhenti.
Karakteristik Motor AC
sinkron
Gambar Model Motor Sinkron (Model dan Diagram Fasor) Pengaruh Penguatan Medan Untuk membangkitkan fluksi dibutuhkan daya reaktif yang bersifat induktif.
- Pada motor sinkron, ggm dibangkitkan arus medan (DC) pada belitan rotor. Jika arus medan ini
- cukup, maka motor tidak membutuhkan supply energi reaktif dari sisi stator yang bersumber dari jaringan listrik. Sehingga motor bekerja dengan faktor daya = 1. Jika penguatan arus medan kurang, maka motor sinkron akan menarik daya reaktif yang bersifat
- induktif dari sisi stator. Sehingga motor bekerja dengan factor daya (pf) terbelakang (lagging). Artinya motor menjadi pembangkit daya reaktif yang bersifat induktif. Kebalikannya jika kelebihan penguatan arus medan, maka motor sinkron akan menarik daya reaktif
- yang bersifat kapasitif dari sisi stator. Sehingga motor bekerja dengan factor daya (pf) mendahului (leading). Artinya motor menjadi pembangkit daya reaktif yang bersifat kapasitif.
Synchronous Generator
Phasor diagram of a synchronous generatorThe phasor diagram is to shows the relationship among the voltages within a phase (E ,V , jX I and R I ) and
φ φ S A A A the current I in the phase. A
Unity P.F (1.0)
Leading P.F. Lagging P.F
Synchronous Generator
Synchronous Generator Power and Torque
In generators, not all the mechanical power going into a synchronous generator becomes electric power out of the machine The power losses in generator are represented by difference between output power and input power shown in power flow diagram below
Synchronous Generator
Rotor
- resistance; iron parts moving in a magnetic field
causing currents to be generated in the rotor body- resistance of connections to the rotor (slip rings)
Stator - resistance; magnetic losses (e.g., hysteresis) Mechanical - friction at bearings, friction at slip rings Stray load losses- due to non-uniform current distribution
Synchronous Generator
The input mechanical power is the shaft power in the generator given by equation:
The power converted from mechanical to electrical form internally
is given byThe real electric output power of the synchronous generator can be
expressed in line and phase quantities as and reactive output powerSynchronous Generator
In real synchronous machines of any size, the armature resistance RA is more than 10 times smaller than the
synchronous reactance XS (Xs >> RA). Therefore, RA can
be ignoredSynchronous Generator
Power flow
Synchronous Generator
FIGURE 8–26 A schematic showing the motor controls for a Lexus RX 400h. Note
the use of the rear motor to provide 4WD capability.