MABB_Part2

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MESIN ARUS BOLAK-BALIK

TE 1403

Dr. Dedet C. Riawan, ST., M.Eng

Electrical Engineering Department

Institut Teknologi Sepuluh Nopember Surabaya

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Construction of Synchronous Generator

Stator

Rotor

pole

Shaft

Armature

winding

Field

winding

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Construction of Synchronous Generator

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Excitation of Field Windings

1. Static excitation system fed through slip ring and brushes

2. Rotating excitation system mounted on the shaft brushless

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Excitation System with Slip Ring & Brushes

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Brushless Excitation System

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Interaction of Rotor & Stator Magnetic Fileds

No-load operation

Br induces EA at stator

Vφ = EA

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On-load operation

• Stator is connected to a load

• IA flows in stator producing magnetic field BS

• BS induces ESTAT at its own stator winding

• EA =Vφ + ESTAT

Armature reaction voltage

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On-load operation

Br coincide with EA

BS coincides with ESTAT

Thus Bnet will coincide with Vf

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Equivalent Circuit with Armature Reaction

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Armature Reaction & Self-Inductance Voltage

Synchronous Reactance

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Phasor Diagram of Synchronous Generator

Unity power factor

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Lagging power factor

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Leading power factor

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Power & Torque in Synchronous Generator

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Power Angle in Synchronous Generator

If RA << XA RA is ignored

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Parameters of Synchronous Generator

1. Relationship between field current and flux (and therefore between the

field current and EA)

2. The synchronous reactance

3. Armature resistance

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Open-Circuit Test

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Open-Circuit Characteristic

SaturatedUnsaturated

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Short-Circuit Test

Vφ = 0

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Short-Circuit Characteristic

Unsaturated

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Determining the Synchronous Reactance

From OCC

From SCC

For a given field current IF

Given IF

VOC

IA

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Limitation on OCC-SCC method

Note:

• EA is obtained from OCC ranging from unsaturated to saturated region

• IA is obtained from SCC unsaturated region

Accurate up to unsaturated synchronous reactance

XS,u

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0

100

200

300

400

500

600

700

800

900

1000

0 100 200 300 400If (A)

I s c ( A )

0

2

4

6

8

10

12

14

16

18

20

If (A)

V o c ( k V )

Example of OCC & SCC test results

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Armature Reaction & Leakage Reactance

Test with Zero Power Factor (ZPF) at IA rated.

Bnet = BR + BS

Bnet ~ Er

BR ~ Ea

Bstat ~ -Ear

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Potier’s Method

1.Find P from ZPF test

2.Find P’ from SCC

3.Draw RP = OP’

4.Draw RS parallel to initial of OCC slope(OS’)

5.Draw SQ perpendicular to RP

Procedure:

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Potier’s Method

SQ = I A xl

PQ = BS

Voltage drop due to leakage reactance

Magnetic flux due to armature reaction = If ar ~ Ear

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Flux and Induced Voltage in Synchronous Generator

Bnet = BR + BS

Er = Ea – Ear

Vt = Er - IAXl

where

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Paralleling Synchronous Generators

Purpose of paralleling generator:

1. Meet the demand on loads

2. Increasing reliability

3. Scheduling and maintenance

4. Load sharing for efficient operation

8-MW

8-MW

8-MW

4-MW

4-MW

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Requirements:

• The rms line voltages of the two generators must be equal.

• The two generators must have the same phase sequence.

• The phase angles of the two a phases must be equal.

• The frequency of the new generator, called the oncoming generator, must beslightly higher than the frequency of the running system.

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Procedure of Paralleling Synchronous Generators

1. Adjust field current until terminal voltage of two generators are equal in

magnitude.

2. Checked phase sequence of two generators. They must be equal.

3. Adjust the frequency of oncoming generator slightly higher.

4. Close the tie breaker

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If the rms line voltages of the two generators IS NOT equal

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If the two generators DO NOT have the same phase sequence

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If the phase angles of the two a phases IS NOT equal

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If the frequency of the two generators IS NOT equal

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If the frequency and phase sequence of the two generators ARE NOT equal

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Speed Governor in Stand-Alone Operation

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Speed Droop Principle

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Speed Droop Principle

Concept of Speed Droop

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Speed Droop in Stand-alone Operation

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Speed Droop in Parallel Operation with Infinite Grid

S d D i P ll l O i i h I fi i G id

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f nl’

P G’

P load’

Set point increased

P i n f b u s ’

S d D i P ll l O ti ith I fi it G id

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Two Same Size Generator in Parallel Operation

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Second generator takes small amount of load

demand during the first moment of

synchronization (PG2)


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Speed of the second generator is increased to

take more load from other.


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Power Sharing in Parallel Operation

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Power Sharing without shifting system frequency


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S a g a a Op a

Power Sharing without shifting terminal voltage

Synchronous Motor

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y

Three phase winding of stator produces rotating

magnetic field BS

If field winding on rotor is excited with current,

magnetic field BR is produced. This magneticfield will “chase” BS.

So, rotor will rotate in the same speed as rotating

magnetic field generated by stator synchronous

Synchronous Motor

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y

Synchronous Motor

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From Generating to Motoring Operation

Synchronous Motor

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From Generating to Motoring Operation

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Load Changes on Synchronous Motor

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Field Excitation Changes on Synchronous Motor

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Under-excited Over-excited

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Starting Synchronous Motor

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Basic Approach

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Reducing Electrical Frequency

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Low frequency slow rotating magnetic field rotor is capable to

accelerate

Stator frequency is then increased gradually up to nominal value.

Requires variable frequency variable voltage source

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Armotisseur or Damper Winding

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Damper winding



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MABB_Part2

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