04 05 Paralel
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KONVERSI TENAGA LISTRIK1:Klasifikasi mesin-mesin listrik dan konstruksi 2:Generator sinkron: proses terbangkitnya EMF dan macam-macam generator sinkron 3:Generator sinkron: berbeban, kerugian tegangan, diagram vektor untuk pf. lagging, pf. leading 4:Generator sinkron: menentukan voltage regulator dengan metode EMF dan karakteristik 5:Generator sinkron: kerja paralel 6:Motor sinkron: metode start dan pengaruh perubahan arus eksitasi 7:Motor sinkron: torque dan contoh soal
*References1. Chapman, S. J, Electric Machinery Fundamentals, McGraw-Hill, 20052. 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
*Examples: Loaded Synch. GeneratorsEx 32-1432-16
*Parallel operation of AC Generator In todays 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 the loads on the system.
*Advantages of parallel operation of AC GeneratorSeveral 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 and maintenance.If only one generator is used and its not operating at near full load, then it will be relatively inefficient. With several smaller machine in parallel, its possible to operate only a fraction of them. The ones that operate are operating near full load and thus more efficiently.
*The conditions required for parallelingG2 is about to be paralleled with G1 by closing 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.
*The conditions required for parallelingTo avoid this problem, each of the three phases must have exactly the same voltage magnitude 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
*The conditions required for parallelingTo achieve this match, the following paralleling conditions must be met: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 oncoming generator must be the same with the line frequency.
*The conditions required for parallelingTo achieve this match, the following paralleling conditions must be met: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 oncoming generator, must be slightly higher than the new frequency of the running system.So that when its connected, it will come on the line supplying power as a generator, instead of consuming it as a motor would.
**Synchronizing of Alternators First, its necessary that the incoming alternators phases are connected in the proper order (R, S, T and not R, T, S).
Then its needed to synchronize each phase. (Its necessary to synchronize one phase only, the other two phases will then be synchronized automatically.)
*Checking phase sequenceCan 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
*Checking phase sequence3-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 the systems have the same phase sequence.If the bulbs brighten in succession, then the systems have the opposite phase sequence.
*Checking whether the systems are in phaseBulb methodDark method (like the previous slide)R to R, S to S, T to TBright methodR to S, S to T, T to RBright-dark methodsee next slide
*Method 2 bright, 1 dark  (1)3 lamps are used, but they are deliberately connected asymmetrically.SSTTTS
*Method 2 bright, 1 dark (2)This transposition of 2 lamps is suggested by Siemens & Halske to help to indicate whether the incoming machine is running too fast or too slow.If lamps were connected symmetrically, they would dark out or glow up simultaneously.**SSTTTS
*Method 2 bright, 1 dark (3)2 sets of star vectors will rotate at unequal speed if the frequencies of the 2 machines are different.
If the incoming alternator is running faster, the voltage star RST will appear to rotate anticlockwise with respect to RST.
*Faster incoming alternatorVoltage across L1 is RR.Its seen increasing from zero.Voltage across L2 is ST which is decreasing.Voltage across L3 is ST which is increasing.Here, the lamps will light up one after the other in the order 2, 3, 1 or 1, 2, 3.
*Slower incoming alternatorIf the incoming machine is slower;The star RST will appear to rotating clockwise relative to RST.Voltage across L2 is ST which is increasing.Voltage across L3 is ST which is decreasing.Here, the lamps will light up one after the other in the order 3, 2, 1.
*Usually the three lamps are mounted at the three corners of a triangle.The apparent direction of rotation of light indicates whether the incoming alternator is running too fast or to slow.Synchronization is done at the moment the uncrossed lamp L1 is in the middle of dark period.When L1 is dark, the other two lamps are dimly but equally bright. -> 2 bright 1 dark method.
*SynchroscopeSynchronization by lamps is not quite accurate because it depends on the sense of correct judgment of the operator.Hence, the machines are synchronized by a more accurate device called synchronoscope / synchroscope.In large generators belonging to power systems, synchronization is automated.
*Synchronizing Current Once synchronized properly, two alternators continue 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 it back to synchronism.
*Synchronizing Current (2)When in exact synchronism no current circulating in the local circuit.Because the two alternators have equal terminal voltages.
*Synchronizing Current Now suppose that due to change in the speed of the 2nd machine, E2 falls back by a phase angle of electrical degrees
*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 and motoring current with respect to alternator 2.
This current Isy sets up a synchronizing torque which tends to retard the generating machine (alternator 1) and accelerates the motoring machine (alternator 2).
*Similarly, if E2 tends to advance in phase: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 synchronizing current Isy which sets up synchronizing torque.
**In the case of two generators operating together:Pload = PG1 + PG2 (+)Power sharing
Electrical DegreeA 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 same polarity. 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.*