A new generation of digital protections used at the synchronous machines allows to shorten the time of the short circuit duration and to cancel the failure states out. Along with it the demands for the adaptation and exact setting of the protections are rising up.

	In the contribution there was an analysis of the alternator protections switching-off time made up. There were also the demands for the exciting system parameters of the generator whitch are to keep the dynamic stability during the various transient processes judged in the same contribution.