an infinite bus bar may be treated like a m/c with large
amount of inertia, so that the frequency will not change.
and the voltage and frequency remains unchanged regardless
of the equipment connected to it.
Infinite bus bar is the source where n numbers of
generators are loaded thereby impedance of the system
becomes so high that connecting or disconnecting any load
does not impact on voltage,frequency of the system.
The Voltage , Frequency of Infinite Busbars always remains
constant. This is what is called as Grid also