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KONVERSI TENAGA LISTRIK

1: Klasifikasi mesin-mesin listrik dan konstruksi 2: Generator sinkron: proses terbangkitnya EMF dan macam-

macam generator sinkron

3: Generator sinkron: berbeban, kerugian tegangan, diagramvektor untuk pf. lagging, pf. leading

4: Generator sinkron: menentukan voltage regulator denganmetode EMF dan karakteristik

5: Generator sinkron: kerja paralel

6: Motor sinkron: metode start dan pengaruh perubahan aruseksitasi

7: Motor sinkron: torque dan contoh soal

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References

1. Chapman, S. J, ‘Electric Machinery Fundamentals’,

McGraw-Hill, 2005

2. Theraja, B. L., ‘Electrical Technology’, S. Chand &

Company Ltd., 1978.

3. Karady, G., ‘Lecture Notes on Synchronous Generator’,

www.eas.asu.edu/~karady/360_pp.html.

3. Zuhal

http://www.eas.asu.edu/~karady/360_pp.html

http://www.eas.asu.edu/~karady/360_pp.html

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Examples: Loaded Synch. Generators

Ex 32-14 32-16

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Parallel operation of AC Generator [1]

In today’s world, an isolated synchronous generator supplying its own load independently of other

generators is very rare.

Such a situation is found in only a few applications

such as emergency generators. For all usual generator applications, there is more

than one generator operating in parallel.

An extreme example of this is the US power grid, in

which literally thousands of generators share theloads on the system.

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Advantages of parallel operation of AC

Generator

Several generators can supply a bigger load than one machine by itself.

Increases the reliability of the power

system.

Allows one or more generators to be

removed for shutdown andmaintenance.

If only one generator is used and it’s

not operating at near full load, then it

will be relatively inefficient. With

several smaller machine in parallel, it’spossible to operate only a fraction of

them. The ones that operate are

operating near full load and thus more

efficiently.

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The conditions required for paralleling

G2 is about to be paralleled with G1 byclosing the switch S1.

If S1 is closed arbitrarily at some

moment, the generators are liable to be

severely damaged, & the load may lose

power. If the voltages are not exactly the

same in each conductor being tied

together, there will be a very large

current flow when the switch is

closed.

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To avoid this problem, each of the three phases must have

exact ly th e same vo ltage

magn i tude and phase angle as

the conductor to which it is

connected.

-> The voltage in phase a must

be exactly the same as the

voltage in phase a’, & so forth for

phases b-b’, and c-c’

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To achieve this match, the following paral lel ing condi t ions must be met:

The rms line voltages of the two generators must be

equal.

The two generators must have the same phasesequence.

The phase angles of the two a phases must be

equal.

**The frequency of the oncoming generator must bethe same with the line frequency.

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To achieve this match, the following paral lel ing condi t ions must be met:

The rms line voltages of the two generators must be

equal.

The two generators must have the same phasesequence.

The phase angles of the two a phases must be

equal.

**The frequency of the oncoming generator , mustbe slightly higher than the new frequency of the

running system.

So that when it’s connected, it will come on the line

supplying power as a generator, instead of consuming it

as a motor would.

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*Synchronizing of Alternators [2]

First, it’s necessary that the incoming alternator’sphases are connected in the proper order (R’, S’, T’

and not R’, T’, S’).

Then it’s needed to synchronize each phase. (It’snecessary to synchronize one phase only, the other

two phases will then be synchronized

automatically.)

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*Checking phase sequence

Can be checked through different ways: Alternately connect a small induction motor to the terminals

of each of the two generators. If the motor rotates in the same direction each time -> phase

sequence is the same. Otherwise, phase sequence differs -> two of the conductors of the

incoming generator must be reversed.

phase rotation check hyoki 3123

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*Checking phase sequence

3-light-bulb method (Fig. 5-27) As the phase changes between the two systems, the

light bulbs first bright (large phase difference),

..and then get dim (small phase difference).

If all three bulbs get bright and dark together, then thesystems have the same phase sequence.

If the bulbs brighten in succession, then the systems

have the opposite phase sequence. 12

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*Checking whether the systems are in

phase

Bulb method Dark method (like the previous slide)

R to R’, S to S’, T to T’

Bright method

R to S’, S to T’, T to R’

Bright-dark method see next slide

http://msdaif.googlepages.com/Synchronization.swf

http://weh.maritime.edu/synchro/

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Method ‘2 bright, 1 dark’ [2] (1)

3 lamps are used, but they are deliberatelyconnected asymmetrically.

S

S

T

T

T’ S’

S’ T’ T S

R’

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Method ‘2 bright, 1 dark’ (2)

This transposition of 2 lamps is suggested bySiemens & Halske to help to indicate whether theincoming machine is running too fast or too slow.

If lamps were connected symmetrically, they woulddark out or glow up simultaneously.**

S

S

T

TT’ S’

S’ T’ T S

R’

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Method ‘2 bright, 1 dark’ (3)

S

T

T’

S’

2 sets of star vectors will rotateat unequal speed if the

frequencies of the 2 machines

are different.

If the incoming alternator is

running faster, the voltage star

R’S’T’ will appear to rotate

anticlockwise with respect to

RST.S’ T’ T S

R’

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Faster incoming alternator

S

T

T’

S’

Voltage across L1 is RR’. It’s seen increasing from

zero.

Voltage across L2 is S’Twhich is decreasing.

Voltage across L3 is ST’

which is increasing.

Here, the lamps will light upone after the other in the

order 2, 3, 1 or 1, 2, 3.

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Slower incoming alternator

S

T

T’

S’

If the incoming machine is slower; The star R’S’T’ will appear to

rotating clockwise relative to RST.

Voltage across L2 is S’T which is

increasing. Voltage across L3 is ST’ which is

decreasing.

Here, the lamps will light up

one after the other in theorder 3, 2, 1.

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S

T

T’

S’

S

T

T’

S’

Usually the three lampsare mounted at the threecorners of a triangle.

The apparent direction of rotation of light indicateswhether the incomingalternator is running toofast or to slow.

Synchronization is done atthe moment theuncrossed lamp L1 is inthe middle of dark period.

When L1 is dark, the other two lamps are dimly butequally bright. -> ‘2 bright1 dark’ method.

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Synchroscope

Synchronization by lamps is not quite accurate becauseit depends on the sense of correct judgment of theoperator.

Hence, the machines are synchronized by a moreaccurate device called synchronoscope /synchroscope.

In large generators belonging to power systems,synchronization is automated.

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Synchronizing Current [2]

Once synchronized properly, two alternatorscontinue to run in synchronism.

Any tendency on the part of one to drop out of

synchronism is immediately counteracted by the

production of a synchronizing torque which brings itback to synchronism.

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Synchronizing Current (2)

When in exact synchronism nocurrent circulating in the local

circuit.

Because the two alternators

have equal terminal voltages.

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Synchronizing Current [2]

Now suppose that due tochange in the speed of the 2nd

machine, E2 falls back by a

phase angle of α electrical

degrees

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Now they have a resultant voltage Er which circulates a current ->

synchronizing current, Isy.

It can be seen that Isy is generating

current with respect to alternator 1 andmotoring current with respect to

alternator 2.

This current Isy sets up a

synchronizing torque which tends toretard the generating machine

(alternator 1) and accelerates the

motoring machine (alternator 2).

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Similarly, if E2 tends to advance inphase:

Isy is being the generating current for

no. 2, tends to retard it and being

motoring current for no. 1, tends to

accelerate it.

Hence, any departure from

synchronism results in the

production of a synchronizingcurrent Isy which sets up

synchronizing torque.

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**In the case of two generators operating

together:

Pload = PG1 + PG2 (+…) Power sharing

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Electrical Degree

A unit of measurement of time as applied to alternating

current. One complete cycle =360 electrical degrees. One

cycle in a rotating electric machine is accomplished when the

rotating field moves from one pole to the next pole of the samepolarity. There are 360 electrical degrees in this time period.

Therefore, in a two pole machine there are 360 degrees in one

revolution, and the electrical and mechanical degrees are

equal. In a machine with more than two poles, the number of

electrical degrees per revolution is obtained by multiplying the

number of pairs of poles by 360.

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