Bab 7 MOTOR AC SINKRON - Bab 7 Motor AC

(1)

Edit by:

Ir. Harlianto Tanudjaja,

M.Kom,MM.

Bab 7

(2)

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

(3)

Electric Motor Family

Tree

(4)

(5)

L

If a conductor of length 0.4m carrying a current of 10.6A is placed in a magnetic field with a flux density of 0.03T, determine the force

experienced by this conductor in newtons.

(6)

South pole Each digit of your hand must be at right

angles to both of the other two

current

_field

motion

Fleming’s Left Hand Rule

(7)

Force

Each digit of your hand must be at right angles to both of the other two

first finger

If the current is reversed, the direction of motion will change

The Motor Effect

(8)

Each digit of your hand must be at right angles to both of the other two

If the field is reversed, the motion will be in the opposite direction

The Motor Effect

(9)

I B

F _f_irst _finger

thumb Each digit of your hand must be at right angles to both of the other two

field

motion

If the field is reversed, the motion will be in the opposite direction

South pole

North pole

(10)

field is clockwise

Current into page

field is anticlockwise

Current out of page

(11)

(12)

(13)

AC Machines

1. Select the proper ac motor type for

various applications.

2. State how torque varies with speed

(14)

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

(15)

Sumber : http://dunia-listrik.blogspot.com/

Klasifikasi Motor Listrik Berdasarkan

(16)

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

(17)

(18)

Synchronous

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

(19)

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

k

ompres

or udara

,

perubahan frekuensi dan generator motor. Motor sinkron

mampu untuk memperbaiki faktor daya sistem,

sehingga

sering

digunakan

pada

sistem

yang

(20)

Prinsip Kerja Motor AC Sinkron

Sebuah motor sinkron dapat dinyalakan oleh sebuah motor dc pada satu sumbu.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 menarik motor hingga mencapai sinkronisasi disebut pull-in torque.

(21)

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

(22)

Kontruksi Motor AC

sinkron

Motor sinkron adalah motor ac yang memiliki kecepatan konstan, namun kecepatan dapat diatur karena kecepatannya berbanding lurus dengan

(23)

(24)

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

(25)

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



(26)

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

(27)

AC Motor



As in the

DC motor

case, a current is

passed through the

coil, generating a

torque on the coil.

(28)

(29)

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

(30)

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

machines are

(31)

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

(32)

Synchronous Machine

Construction-Rotor



i) Cylindrical (or round)

rotor



i) Salient-pole

(33)

1. Most hydraulic turbines have to turn at low speeds

(between 50 and 300 r/min)

2. A large number of poles are required on the rotor

(34)

Salient-Pole Synchronous Generator

Stator

Salient-pole

(35)

L » 10 m

 Direct-conductor cooling (using hydrogen or water as coolant)

 Rating up to 2000 MVA

Turbogenerator

d-axis

q-axis

(36)

Cylindrical-Rotor Synchronous Generator

Stator

(37)

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

(38)

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

(39)

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

(40)

Synchronous Machine –

Stator construction

3 p

has

(41)

AC Synchronous Motor

Operation

41

• 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

ELO 2.6

(42)

AC Synchronous Motor

Operation

42

• 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

(43)

AC Synchronous Motor

Operation

43

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

(44)

AC Synchronous Motor

44

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

(45)

AC Synchronous Motor

45

Knowledge Check

Select all of the statements about AC synchronous motors that are true.

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.

(46)



Magnetomotive Forces (MMF’s) and Fluxes

Due to Armature and Field Windings

Synchronous Machine

Flux produced by a

stator

winding

(47)

Developing Torque –

Single-Phase

AC Motor

47

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.

(48)

(49)

(50)

Further Study - AC Motor Performance

Synchronous Cage Induction Wound induction

(51)

Synchronous Generator

(52)

Synchronous Speed

2 P

s





(53)

Matematis Motor AC

sinkron

Slip dari motor AC dihitung

dengan :

Di mana :

N

_r

= Kecepatan putar, dalam

rpm

S = Slip normal, 0 sampai 1.

(54)

Synchronous

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.

(55)

Matematis Motor AC

sinkron

Motor ini berputar pada kecepatan sinkron, yang diberikan oleh persamaan berikut :

Ns = 120 f / P

di mana :

N_s = kecepatan serempak, dalam rpm

F = frekuensi daya AC

(56)

(57)

(58)

(59)

(60)

Effect of Rotor

Inductance on Torque

c

L

js

R







V

(61)



_{If the generator operates at a terminal voltage}

_V

_T

_while

supplying a load corresponding to an armature current

Ia

,

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}

(62)

(63)

(64)

(65)

(66)

(67)

(68)

(69)

(70)

Penggunaan Motor AC

sinkron

(71)



_{A three-phase, wye-connected 2500 kVA and 6.6}

kV generator operates at full-load. The

per-phase armature resistance

R

_a

and the

synchronous reactance,

X

_d

, are (0.07+j10.4)



.

Calculate the percent voltage regulation at

(a)

0.8 power-factor lagging, and

(b)

0.8 power-factor leading.

(72)

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)

(73)

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.

(74)

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.

(75)

Pengukuran Motor AC

sinkron

Pembangkitan Torka

•Interaksi antara medan putar stator (B_s) dan medan rotor (B_r) yang

membangkitkan torka seperti terlihat dalam persamaan berikut :

T = B_sx B_s(sin δ)

•_{δ disebut sudut beban karena besarnya tergantung pembebanan. Pada saat}

beban nol nilai δ = 0. Jika dibebani, medan rotor tertinggal dari rotor sebesar δ,

kemudian berputar sama lagi. Beban maksimum tercapai pada δ = 90o_{. Jika}

beban dinaikkan terus melebihi batas itu, maka motor akan kehilangan

(76)

Pengukuran Motor AC

Tiap arus fasa membangkitkan ggm F yang merupakan fungsi sudut ruang  seperti :

i_a à F_a.cos θ. Dengan F_a=F_m. sin ωt

Maka ggm F tiap fasa yang dibangkitkan :

F_a = F_m sin ωt.cos θ

F_b = F_m sin (ωt-120o_{).cos (θ-120}o₎

F_c = F_m sin (ωt-240o_{) .cos (θ-240}o₎

(77)

Pengukuran Motor AC

sinkron

Jika kemudian disederhanakan dengan persamaan trigonometri akan diperoleh:

F(θ,t) = 3/2 F_m.cos (θ-ωt)

(78)

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 positif pada generator sinkron. Torka maksimum dicapai pada δ= +/- 90o_{. Jika}

(79)

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}