Advantages and condition of Parallel Operation of synchronous generator
Advantages of Parallel Operation of Alternators:
The following are the advantages of operating alternators in parallel:
(i) Continuity of service.
The continuity of service is one of the important requirements of any electrical apparatus. If one alternator fails, the continuity of supply can be maintained through the other healthy units. This will ensure uninterrupted supply to the consumers.
The load on the power system varies during the whole day; being minimum during die late night hours. Since alternators operate most efficiently when delivering full-load, units can be added or put off depending upon the load requirement. This permits the efficient operation of the power system.
(iii) Maintenance and repair.
It is often desirable to carry out routine maintenance and repair of one or more units. For this purpose, the desired unit/units can be shut down and the continuity of supply is maintained through the other units.
(iv) Load growth.
The load demand is increasing due to the increasing use of electrical energy. The load growth can be met by adding more units without disturbing the original installation
Conditions for Paralleling Alternator with Infinite Busbars:
The proper method of connecting an alternator to the infinite busbars is called synchronizing. A stationary alternator must not be connected to live busbars. It is because the induced e.m.f. is zero at standstill and a short-circuit will result. In order to connect an alternator safely to the infinite busbars, the following conditions are met:
(i) The terminal voltage (r.m.s. value) of the incoming alternator must be the same as busbars voltage.
(ii) The frequency of the generated voltage of the incoming alternator must be equal to the busbars frequency.
(iii) The phase of the incoming alternator voltage must be identical with thephase of the busbars voltage. In other words, the two voltages must be in
phase with each other.
(iv) The phase sequence of the voltage of the incoming alternator should be the same as that of the busbars.
The magnitude of the voltage of the incoming alternator can be adjusted by changing its field excitation. The frequency of the incoming alternator can be changed by adjusting the speed of the prime mover driving the alternator. Condition (i) is indicated by a voltmeter, conditions (ii) and (iii) are indicated by
synchronizing lamps or a synchroscope. The condition (iv) is indicated by a phase sequence indicator.