Not for sure what you really are asking. When you connect a generator on line to an electric system, you have to make sure it is in sync with the system you are connecting to. You use a synch check scope or meter to check between your generator and system before you close the breaker to tie in the generator. The generator is usually connected to a steam turbine. Here in the USA the turbine will be rotating at 3600 rpm, called synchronous speed.