*ALTERNATORGenerator AC atau generator sinkron sering disebut Alternator, karena membangkitkan tegangan dan arus AC (Alternating Current)

Pembangkitan Gelombang AC*

Pembangkitan Gelombang AC*

Nilai Tegangan*

*Tegangan Terinduksi sbg fungsi waktu

*Tegangan / Arus Bolak-Balik 3 Fase

*Alternating CurrentNilainya berubah terhadap waktuMempunyai puncak, zero cross, lembahMempunyai frekuensi (f)

*1. Rangka stator terbuat dari besi tuang2. Stator bagian inti yang tersusun dari plat-plat, yang mempunyai alur3. Rotor bagian yang berputar, terdapat kutub-kutub magnet dengan lilitannya yang dialiri arus searah, melewati cincin geser4. Generator penguat sebagai sumber arus medanKonstruksi Alternator

ConstructionStatorMechanicalRotorArmatureElectrical Field

* Stator

Penghantar dalam alur (slot)*

Stator ConstructionSingle layerStator Slots1 coil arm per slotCoil

Stator ConstructionDouble layerStator SlotsCoil2 coil arms in each slot

Stator ConstructionStators can be very large

Penghantar *

Penampang melintang penghantar*

Rotor*

Synchronous GeneratorsView of a two-pole round rotor generator and exciter. (Westinghouse)

Synchronous GeneratorsConstruction of a two-pole salient pole generatorField WindingsArmature Windings

Salient Pole GeneratorRotor of a four-pole salient pole generator

*BAGIAN UTAMA ALTERNATORStatorMerupakan bagian alternator yang diam.Umumnya digunakan sebagai tempat kumparan jangkarContoh Stator 3 Fase 500 MVA, 15 kV

*BAGIAN UTAMA ALTERNATORRotorMerupakan bagian yang berputarUmumnya digunakan sebagai tempat kumparan medanContoh Rotor 36 kutub dg arus eksitasi 2400 A

*

*Tipe RotorAda 2 tipe kutub pada rotorKutub menonjol (salient pole)Kutub silinder (cylindrical pole)Kutub MenonjolKutub Silinder

Rotor ConstructionSalient PoleDifference between pole face curvature and stator creates non-linear variation in flux across pole faceNon-linear variation in flux across pole face produces sinusoidal change in the induced EMF

Contoh Name Plate Alternator Unit #2 di PLTA SAGULING*

Kutub-kutubnya terletak di rotor*

*Alternator dengan kecepatan tinggi umumnya menggunakan kutub silindris

Rotor ConstructionCylindricalDifference in coil spacing creates non-linear variation in flux around the rotor surfaceNon-linear variation in flux around rotor surface produces sinusoidal change in the induced EMF

Rotor ConstructionCylindricalDifference in coil spacing creates non-linear variation in flux around the rotor surfaceNon-linear variation in flux around rotor surface produces sinusoidal change in the induced EMF

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POLYPHASE SYNCHRONOUS MACHINESTwo types: 1-Cylindirical rotor: High speed, fuel or gas fired power plants 2-Salient-pole rotor: Low speed, hydroelectric power plants To produce 50 Hz electricityp=2, n=3000 rpmp=4, n=1500 rpmTo produce 50 Hz electricityp=12, n=500 rpmp=24, n=250 rpm

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

How does a synchronous generator work?1- Apply DC current to rotor winding (field winding)2- Rotate the shaft (rotor) with constant speed.3- Rotor magnetic field will create flux linkages in stator coils and as a result voltage will be produced because of Faradays Law.

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

How is DC current applied to the rotor?1- Slip RingsNote: Magnetic field of rotor can also be produced by permanent magnets for small machine applications2- Brushless Excitation System: Excitation supplied from ac exciter and solid rectifiers. The alternator of the ac exciter and the rectification system are on the rotor. The current is supplied directly to the field-winding without the need to slip rings.

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

Synchronous generators work in parallel with the interconnected system. Frequency and voltage are constant.The behivor is examined based on a generator connected to an INFINITE BUS.Infinite busf : constantV : constantGenerator

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

Open-circuit characteristic of a synchronous machine.

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

Typical form of an open-circuit core-loss curve.

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

Open- and short-circuit characteristics of a synchronous machine.

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

Characteristic form of synchronous-generator compounding curves.

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.5-*

Typical form of synchronous-generator V curves.

*Generator Penguat (Exciter)Ada 2 tipe exciter :

a. Dengan komutator dan sikatb. Tanpa sikat

Exciter berfungsi untuk mensuplai arus DC ke kumparan medan

*Skema exciter yang mensuplai arus DC melalui komutator dan sikat

*Sistem eksitasi menggunakan sikat (brush excitation)

*Sistem eksitasi menggunakan sikat (brush excitation)

*Sistem Exciter Tanpa Sikat

*Sistem eksitasi tanpa sikat (brushless excitation)

*Penguatan dengan Sistem Brushless

Eksternal Eksitasi*

*Arus medan akan mempengaruhi fluks magnet dan akhirnya akan mempengaruhi juga GGL yang dibangkitkan

*Ditinjau dari jumlah fasenya alternator dibedakan menjadi alternator fase tunggal dan alternator 3 fase

Skema alternator fase tunggal dua kutub

*Skema alternator 3 fase dua kutub

*Bentuk gelombang tegangan dan diagram fasor 3 fase

*Gaya Gerak Listrik (Electromotive force)GGL setiap fase dirumuskan sebagai

Emax = Bm l r (volt)

Dimana : Bm = Kerapatan fluks maksimum (T) l = panjang kedua sisi koil dalam medan magnet (m) = kecepatan sudut rotor, (rad/s ) (= 2 frekuensi) r = radius armature (m)

*Contoh :Sebuah generator AC, 2 kutub, membangkitkan tegangan 3 fase dengan urutan ABC. Diasumsikan memiliki data sbb; Bm = 1,2 T, panjang armatur 0,5 m, kecepatan rotor 1500 rpm dan diameter sisi dalam inti stator 0,4 m.

hitunglah tegangan yang diinduksikan per faseberapakah frekuensinya

*Penyelesaian :GGL maksimum (Emax ) =Emax = 37,7 V

Operation ConceptsOperating concept of a synchronous generator

Flux LinkageFlux linkage variation.(a) Flux is perpendicular to phase A(b) Flux is parallel to phase A

Rotating FluxRotating flux linkage to phase A.

EMF EquationAccording to Faradays law, the induced emf in the armature coil of Nsta turns is given by:

*ALTERNATORKeluaran (out put) alternator berupa Gaya Gerak Listrik (GGL) yang memiliki frekuensi.Frekuensi yang ditimbulkan oleh alternator bergantung pada jumlah kutub dan kecepatan putar rotornya. f = frekuensi (Hz).p = jumlah kutub per fase (buah)n = kecepatan rotor ( rpm)

*ContohAda sebuah generator AC dioperasikan pada kecepatan 1800 rpm.Berapa frekuensi yang dibangkitkan ?Berapa kecepatan rotor agar frekuensi generator menjadi 50 Hz. ?

Speed and FrequencynS is the synchronous speed (r/m)f is the frequency in Hz.2P = total number of poles.

Example: calculate the frequency of a 1800 rpm , 4 pole synchronous generator ns = 1800 r/m, 2P = 4 Then, f = 2*1800/60 = 60 Hz