MESIN ELEKTRIK I

Oleh : Ir. Hery Purnomo, MT

Mesin sinkron

APLIKASI

MESIN SINKRON (Mesin Serempak)

1.Generator Sinkron a). Generator sinkron 3 fasa

b). Generator sinkron 1 fasa

PLTA, PLTD,PLTU, PLTG, PLTGU, PLTN, ………..dsb.(Pembangkit tenaga listrik arus bolak-balik)

2.Motor sinkrona). Motor sinkron 3 fasa motor penggerak beban mekanik kapasitas besar

P>200 HP, tegangan menengah (4000 – 6000V)b). Motor sinkron 1 fasa motor penggerak mekanik ukuran kecil, yang digunakan

pada peralatan kontrol (motor servo, motor sinkro)

Konstruksi Mesin Sinkron

1.Mesin sinkron Kutub dalam (kutub maknit berputar, dirotor)

2.Mesin sinkron Kutub luar (kutub maknit diam, distator)

Kutub luar

Belitan medan Belitan jangkar / Bel. tenaga

Kutub dalam

Belitan jangkar / Bel. tenaga Belitan medan

Magnet permanen

1). Kutub silindris (non salient pole) 2). kutub tonjol (salient pole)

Mesin sinkron kutub dalam

Kutub tonjol

• Kutub banyak• Putaran rendah (n < 1000 rpm)• Aplikasi : PLTA

8

PLTA

Stator under construction

• Kutub sedikit• Putaran tinggi (n > 1000 rpm)• Aplikasi : PLTU, PLTD, PLTN, …..

Kutub silindris

Steam Turbine(PLTU)

Power Station(PLTN)

Macam belitan Mesin sinkron :1). Belitan Jangkar (belitan stator)2). Belitan medan

Belitan jangkar

Belitan medan

Konsep dasar generator sinkron (kutub luar)

Magnet tetap

Generator sinkron kutub dalam

(Belitan medan)

(Belitan jangkar)

Konsep dasar generator sinkron 3 fasa.

Mesin sinkron 3 fasa, kutub dalam

N

S

a

c b

a'

c'b'

ia

ib

ic

Statorwindings

a'

b'

c'

BSV f

a

b

c

+

–

n

Important Characteristics of Alternators

• The output frequency of an alternator can be varied only

by changing the rotor speed.

• The output voltage of an alternator can be varied by

changing either the field current or the rotor speed.

Important Characteristics of Alternators

• Power losses in the brushes and slip rings is relatively small.– Brushed and slip rings are in the field circuit.– Field current is low.

• The output current capacity of the alternator can be increased simply by increasing the size of the stator wire.– Higher output current will cause a proportional increase in the

input shaft torque.– This will increase in the mechanical stress on the field windings.

• The rotating field causes an alternating field in the stator core.– The core will suffer hysteresis and eddy current losses.– The stator core must be laminated to minimize eddy currents.– The magnetic field in the rotor core is constant, so the rotor core

does not need to be laminated.

Two-pole three-phase alternator armature.

A 12-V dc automotive alternator system.

Output Frequency

• f = (P nr) / 120– f = the frequency in Hertz (Hz)– P = the number of poles per output phase

(dimensionless)

– nr = the rotor speed in revolutions per minute (rpm)

Mesin sinkron 4 kutub

1) Gambarkan bentangan/skema belitan medan2) Gambarkan bentangan belitan jangkar mesin sinkron 1 fasa3) Gambarkan bentangan belitan jangkar mesin sinkron 3 fasa

Rangkaian ekuivalen mesin sinkron

Generator (Appx.)Motor(Appx.)

Generator (Exact)Motor(Exact)

•Only difference is in current direction; in a generator it flowsout of it, in case of a motor it flows into it.

Machine

Machine

Machine

Machine

Rangkaian ekuivalen mesin sinkron

Machine Machine

Xs=Xar+Xal (Synchronous reactance)Zs= Ra+jXs (Synchronous impedance)Xal is leakage ReactanceRa is armature resistance

Generator (Exact)Motor(Exact)

Phasor diagram mesin sinkron

Note: is +ve for (a) generator and –ve for (b) motor

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