The word busbar, derived from the Latin word omnibus ('for all'), gives the idea of a universal system of conveyance. In the electrical sense, the term bus is used to describe a junction of circuit...
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Synchronization of Three Phase Alternator on Busbar Expt. No. Date: OBJECTIVE 1. To synchronize the three phase alternator to the three phase ac bus bar. 2. To study the effect of changing the mechanical input and excitation on alternator.
APPARATUS REQUIRED S.NO 1 2 3 4 5 6 7 8
NAME
TYPE
RANGE
QUANTITY
Ammeter Ammeter Voltmeter Rheostat Tachometer Synchroscope Wattmeter Power Factor meter
THEORY A large generating station normally consists of several ac generators to supply the total load on the station. During light load on the station, only a few generators are operated to supply the demand. When the load on the station increases heavily, other ac generators are also to be operated to run in parallel with the existing generator, in order to cope up with the increased load on the generating station. Synchronizing of ac generators is the process of switching on an incoming alternator to the bus bar, so that it can operate in parallel with other alternators already connected to the bus bar to share the load on the generating station. Before an incoming alternator, can be synchronized to the bus bars, the following conditions must be satisfied. 1. The voltage generated by the incoming alternator is equal to the bus bar voltage. 2. The phase sequence of the generated voltage of incoming alternator is the same as that of bus bar voltage. 3. The frequency of the two system bus to be equal.
CIRCUIT DIAGRAM - SYNCHRONOZIATION SYNC
DC SHUNT MOTOR (+)
A
FUSE
Hz
SYNCHRONOUS GENERATOR
A
R
S
0
C
V
V D 220 V
P
D.C.
S
SUPPLY
T
F1 0 N
M
S
INCOMING M S
OFF
N
A2
S
BR
B
F2
F2
RY
R BYY
Y
B
F1 N
C
FUSE
V M
(-)
Fig - 1 NAME PLATE DETAILS
600 500 400
200
A1
V
S
50 55
A
L
(+)
FUSE
D P S T S
220 V D.C. SUPPLY
FUSE
(-)
FUSE RATING CALCULATION
PRECAUTIONS Before starting and after completion 1.
The DPSTS or dc mains should be in off position.
2.
The motor field rheostat should be in minimum resistance position and armature field rheostat should be in maximum resistance position.
3.
The field rheostat of the alternator should be in minimum potential position.
4.
The TPST switch in the synchronizing panel should be in off position.
PROCEDURE 1. Connections are made as shown in circuit diagram. 2. Precautions are observed and switch on the dc mains. Now the motor will start to run with speed less than synchronous speed. 3. Set the speed of the motor and hence the alternator at its rated value (synchronous speed) as per the line frequency. 4. The terminal voltage of the alternator is adjusted to rated value by adjusting the excitation i.e. by varying the potential divider of alternator rheostat. 5. The voltage and frequency are checked with the meters. 6. Observe the phase sequence and make sure it is proper. Otherwise make suitable corrections. 7. Switch on toggle switches in synchronizing panel. 8. Adjust the speed and voltage of alternator till they are equal to their bus voltage. The synchroscope will rotate at a speed proportional to difference between the two frequencies. 9. When the synchroscope pointer is at null position close the TPST switch. 10. Keep the DC motor input current constant value and vary the alternator excitation and for various excitation note down the armature current. 11. Similarly keep the alternator field constant and vary the DC motor input current and tabulate the V, I for various motor input currents. 12. After taking all the readings readjust the setting of their initial positions and then switch-off the machine.
TABULAR COLUMN Synchronization of 3-f alternator with infinite bus-bar – Effect of change in excitation with constant m S.No.
VL ( Volts )
VDC ( Volts )
IF ( Amps )
IL ( Amps )
PF
P ( Watts )
(
Synchronization of 3-f alternator with infinite bus-bar – Effect of change in mechanical input with con S.No.
VL ( Volts )
VDC ( Volts )
IF ( Amps )
IL ( Amps )
PF
P ( Watts )
(
INFERENCE
RESULT
VIVA – QUESTIONS
1. What will happen, if the synchronization switch is closed at wrong instant? 2. Write down the equation for synchronizing power of a three-phase synchronous generator? 3. Why is it essential to operate alternators in parallel? 4. What is the most commonly used method for checking the frequency equality and same phase sequence is one dark and two bright lamp method? 5. How is synchroscope used for synchronizing alternators? 6. What is the condition of the incoming alternator, when it has been synchronized with the bus-bar?
