Mesin Arus Searah V3TE3110

Jimmy Trio Putra, S.T., M. Eng.

Hukum Dasar Mesin Listrik

HUKUM –HUKUM DASAR DAN PRINSIP UTAMA Hukum Faraday dari induksi elektromagnetik ( ggl dinamis) Tegangan yang dibangkitkan pada suatu batang konduktor yang digerakkan dalam suatu medan magnit ( fluks) menurut Hukum Faraday adalah :

EN

 t

di mana : E = tegangan induksi [volt] = gaya gerak listrik =ggl =emf N = jumlah lilit dari kumparan ΔФ = perubahan fluks pada kumparan [Weber]=[Wb]

Δt = selang waktu saat perubahan flux [detik] 3

Example Sebuah kumparan sebanyak 2000 lilit melingkungi 5 mWb flux yang dihasilkan permanen magnet (Gbr di bawah). Pergerakan magnet selama 1/10 s. Mengakibatkan flux magnet berkurang menjadi 2 mWb. Berapakah tegangan induksi yang terjadi ? N = 2000

N

1  5mWb  2  2mWb

S

N

S

t  1 / 10 s E

4

Hukum Dasar Mesin Listrik (1) • •

Hukum dasar fisika yang berhubungan dengan interaksi parameter magnetik, listrik dan mekanik untuk konversi energi elektrik. Persamaan Gaya Lorentz – Gaya Lorentz adalah gaya yang dihasilkan oleh suatu batang konduktor yang dialiri arus listrik dan ditempatkan dalam suatu medan magnit adalah: I

• F=lIxB Dimana : F = gaya yang terjadi [N]

l

B

S

N

F

Force (F)

penghantar

B = kerapatan flux [T] l = panjang batang konduktor dalam medan magnet [m]

l

I = arus yang mengalir pada batang konduktor [A]

I

B

5

Lorentz’s Law

Besar gaya lorenz : 1. sebanding dengan kuat arus penghantar 2. sebanding dengan panjang penghantar 3. sebanding dengan medan magnet 4. sebanding dengan sinus sudut antara arah arus dan medan magnetik F = B I L sinø

Example Sebuah batang konduktor sepanjang 3 m dilewati arus 100 A dan terletak pada medan magnet dengan kerapatan sebesar 0,5 T. Hitung besarnya gaya yang terjadi apabila batang konduktor diletakan seperti pada gambar A dibawah.

I

l

B

S

N Force (F)

Gbr A Solution

F  BIl  0,5  3  200  300 N 7

Hukum Dasar Mesin Listrik (2) •

Hukum Biot Savart – Intensitas medan magnet H (A/m) yang dihasilkan oleh muatan yang bergerak/arus listrik pada titik P yang tegak lurus dengan jarak R dari penghantar adalah :

• H=

1 2πR

I x ar

F

Rapat medan magnet B yang diakibatkan H : B = μH = μR μo H

H R

Penghantar panjang

μR (permeabilitas relatif) = μ/ μo μ o = 4π x 10-7 H/m

P

aR

I 8

Hukum Dasar Mesin Listrik (3) •

Aturan tangan kanan – Arah medan magnet di sekitar kawat berarus listrik ditentukan dengan aturan tangan kanan.

I

B,H,φ

I

Fluks Magnet :

I

B,H,φ Φ =  B. dA

dA

•

Hukum Faraday –

•

Kumparan dengan N lilitan dilingkupi perubahan Φ menghasilkan tegangan terminal e sebesar : e = N dΦ/dt

Hukum Lenz: Polaritas tegangan e yang dihasilkan perubahan Φ: φ

φ

+

e

-

e

dφ/dt > 0

+

dφ/dt < 0 9

Constructional Features of DC Machines

Small EM Motors

Original Caption by Science Service ©Soviet Foto Agency

The 21-year-old student Yuri Yeremin, of Moscow, established a new record by constructing an electric motor which weighs but 0.37 grams. It consists of 31 parts. The magnetic parts of the motor are made of tin, the current-carrying parts of brass and all insulating parts and the pulleys of ebonite. The diameter of the armature is 4 mm. The compound winding consists of 250 wire windings. The armature has 380 windings of the same wire, 0.05 mm in diameter. The metallic parts of the motor are fixed to its celluloid base by aluminum rivets. This smallest of motors is put into action by a pocket battery of four volts or by the regular city electric current through a bell transformer. Yuri Yeremin is a student of the Moscow Institute for Non-Ferrous Metals. He built his minute motor in 10 days. 11

Large Electrical Machines

Shield Generator, Hoth

12

Operating Principles Generator arus searah berfungsi mengubah energi mekanis dari penggerak mulanya menjadi energi listrik yang diberikan ke beban. Motor arus searah berfungsi mengubah energi listrik yang diterima menjadi energi mekanis berupa kecepatan putar poros yang nantinya dipergunakan untuk memutar peralatan-peralatan produksi di pabrik maupun industry. Perangkat mesin arus searah dapat berfungsi sebagai generator dan pada saat yang lain dapat berfungsi sebagai motor, sehingga bentuk fisik dan konstruksinya sama. Bergantung dari input dan output yang dihasilkan.

DC Motor Advantages of DC Motor:  Ease of Control  Deliver high starting torque  Near-linear Performance Disadvantages:  High Maintenance  Large and expensive (compared to induction motor)  Not suitable for high-speed operation due to commutator and brushes

DC Motor Applications

Constructional of DC Machines Konstruksi utama dari mesin arus searah: 1) Stator: bagian mesin arus searah yang diam. 2) Rotor atau angker atau jangkar atau armature: bagian dari mesin yang berputar. 3) Celah Udara: ruangan yang ada antara stator dan rotor.

Stator dan Rotor Mesin Arus Searah

Construction of DC Machines 1. Yoke:  made up of cast iron or steel.  Its main function is to form a protective covering over the inner sophisticated parts of the machines and provide to the armature.  Responsible to protection of insulating materials that are used inside.  Protects all the components inside from dust, moisture, gases, acidic fumes and particles from the environment.  Serves of mechanical to the poles  It forms a part of the magnetic circuit. It provides a path of low reluctance for magnetic flux.

Construction of DC Machines 2. Poles; divided into: pole core and pole shoe  Pole core basically carries a field winding which is necessary to produce the flux.  It directs the flux produced through air gap to armature core, to the next pole.  Pole shoe enlarges the area of armature core to come across the flux, which is necessary to produce larger induced e.m.f. To achieve this, pole shoe has been given a particular shape.  Made up cast iron or cast steel

Construction of DC Machines 3. Field Winding:  To carry current due to which pole core, on which the field winding is placed behaves as an electromagnet, producing necessary flux.  As it helps in producing the magnetic field i.e. exciting the pole as an electromagnet it is called Field winding or Exciting winding.  Made up aluminium or coper

Construction of DC Machines 4. Armature; divided two parts: Armature core and Armature Windings.  Armature core : Armature core is cylindrical in shape mounted on the shaft. It consists of slots on its periphery and the air ducts to permit the air flow through armature which serves cooling purpose. a) Functions : • Armature core provides house for armature winding i.e. armature conductors. • To provide a path of low reluctance to the magnetic flux produced by the field winding. b) Made up: cast iron or cast steel.

Construction of DC Machines 4. Armature; divided two parts: Armature core and Armature Windings.  Armature winding: is nothing but the interconnection of the armature conductors, placed in the slots provided on the armature core periphery. When the armature is rotated, in case of generator, magnetic flux gets cut by armature conductors and e.m.f. gets induced in them. a) Functions : • Generation of e.m.f takes place in the armature winding in case of generators. • To carry the current supplied in case of d.c. motors. • To do the useful work in the external circuit. b) Made up: copper

Construction of DC Machines 5. Commutator; We have seen earlier that the basic nature of e.m.f. induced in the armature conductors is alternating. This needs rectification in case of d.c. generator, which is possible by a device called commutator. a) Functions : • To facilitate the collection of current from the armature conductors. • To convert internally developed alternating e.m.f. to unidirectional (d.c.) e.m.f. • To produce unidirectional torque in case of motors. • b) Made up: copper segments with mica insulation between two segments

Construction of DC Machines 6. Brushes and Brush Gear. Brushes are stationary and resting on the surface of the commutator. a) Functions : • To collect current from commutator and make it available to the stationary external circuit. b) Made up: soft material like carbon.

Construction of DC Machines 7. Bearings Ball-bearings are usually used as they are more reliable. For heavy duty machines, roller bearings are prederred.

Elementary of DC Machine

• Stator coil as field winding  source of flux • Rotor coil as armature

25

Operating Principles Mesin DC terdiri dari dua belitan (windings): 1. Field winding (Belitan Medan): digunakan untuk menghasilkan medan magnet pada mesin listrik. 2. Armature winding (Belitan Armatur/Belitan Jangkar): digunakan untuk menghasilkan torsi akibat adanya medan magnet dan arus listrik yang bekerja pada belitan tersebut.

Pada belitan armature terjadi perubahan arah arus secara periodic yang mengalir. Mekanisme pembalikan arah arus ini dapat terjadi karena adanya komponen brushes yang melekat pada stator dan komponen commutator yang melekat pada rotor. Ketika commutator berputar, brushes bergerak relative terhadap commutator dari satu segmen ke segmen lainnya sehingga arah arus yang mengalir pada belitan armature berubah.

Constructional of DC Machines Stator terdiri dari: • Gandar (Rumah), terbuat dari besi tuang

Penampang Mesin Arus Searah

• Kutub: a) Inti dari besi lunak atau baja silicon b) Sepatu kutub c) Lilitan dari tembaga

Constructional of DC Machines Rotor atau armature (jangkar/angker) terdiri atas: a) Inti, dengan material besi lunak atau baja silicon b) Belitan (penghantar) dari tembaga c) Komutator dari tembaga d) Sikat dari karbon

Question ?

THANK YOU