Power frequency variations:
ü Power frequency variations are a deviation from the nominal supply frequency. The supply frequency is a function of the rotational speed of the generators used to produce the electrical energy.
ü At any instant, the frequency depends on the balance between the load and the capacity of the available generation.
ü A frequency variation occurs if a generator becomes un-synchronous with the power system, causing an inconsistency that is manifested in the form of a variation.
ü The specified frequency variation should be within the limits +- 2.5% Hz at all times for grid network.