Synchronous generator Connected to Infinite Busbars
Synchronous Machine on Infinite Bus-bars:
Fig: 1 Generator on infinite Bus-Bar -(No load) Fig: 2 Generator on infinite Bus-Bar - (Full load power)
The behavior of a synchronous generator or a pair of synchronous generator supplying a single concentrated load. In view of the tremendous increase in the size of interconnected transmission and distribution systems in the last few decades, and the power generation is contracted at a few large power stations.
The generating plant capacity is of a few hundred or thousand MVAs. In such a plant several generators (of say a few hundred 100 kvAs each) will be operated in parallel. Not all of them will be operating simultaneously as we may not have the demand for the total capacity of the plant all the time.
Assume the behaviour of a single machine connected to this type of a large generating plant is not likely to disturb the voltage and frequency provided the rating of the machine is only a fraction of the total capacity of the generating plant. In the limit, we may presume that the generating plant maintains an invariable voltage and frequency at all points.
In other words a network has zero impedance and infinite rotational inertia. A synchronous machine connected to such a network is said to be operating on infinite bus-bars. As such, we can expect that, characteristics of a synchronous generator on infinite bus-bars are going to be quite different from those when it operates on its own concentrated load.
A change in the excitation changes the terminal voltage, while the power factor is determined by the load, supplied by the stand alone synchronous generator. On the other hand, no alteration of the excitation can change the terminal voltage, (which is fixed by the network) when it is connected to bus bars, the power factor, however, is affected.
In both cases the power developed by a generator depends on the mechanical power supplied. Likewise the electrical power received by a motor depends on the mechanical load applied at its shaft.
Practically all synchronous motors and generators in normal industrial use on large power supply systems can be considered as connected to infinite bus-bars, the former because they are relatively small, the latter on account of the modern automatic voltage regulators for keeping the voltage practical, constant at all loads.
The behaviour of the synchronous machine connected to infinite bus bars can be easily described from the electrical load diagram of a synchronous generator.