I work in a power plant...Heard lot about core saturation. Why does a core (say for ex of a transformer/or an alternator) saturates? is this detrimental??? plz explain

 

It can occur on secondary short circuits (arcing), or on no load conditions if power factor reactances remain in place on the primary, etc., etc.

when it occurs, basically unlimited primary current flows for a moment, at which time the fuses/breakers go (hopefully fast enough)

extremely kinetic failures can occur