State the condition to be satisfied before connecting two alternators in parallel

The following are the three conditions to be satisfied by synchronizing the additional Alternator with the existing one or the common bus-bars.

• The terminal voltage magnitude of the incoming Alternator must be made equal to the existing Alternator or the bus-bar voltage magnitude. 
• The phase sequence of the incoming Alternator voltage
• The phase sequence of the incoming Alternator voltage must be similar to the bus-bar voltage. 
• The frequency of the incoming Alternator voltage must be the same as the bus-bar voltage.