Frequency Change in the Grid

http://en.wikipedia.org/wiki/Frequency_grid

The frequency changed in your grid???? What a disaster!

Change in frequency before affecting generation plant the following things will happen.

If grid frequency increases at constant voltage, then all Power transformers' iron losses (hysteresis + Eddy current) will increase. If the effect is prolonged, then all the transformers in the grid may burn & leading to power blackout in the region.

If Grid frequency decreases at constant voltage, then power will go off fast in the grid due to magnetic saturation in transformers' core. Saturation in transformer core will increase Heavy Copper + Iran losses that lead to burning of transformer & power blackout in the region.