Generally, there are more than three marine generators, including two for daily use and one for standby. The two generators used must be combined.

The parallel operation of alternators must meet four conditions: first, the parallel generators must have the same phase sequence;

The generator voltage of two parallel cars must be the same;

The generators of three parallel cars must have the same frequency;

The generators of four parallel cars must have the same phase angle;

The first one is qualified when wiring, and the second one and the third one are realized in parallel operation. Adjust the generator excitation to make the voltage the same; Adjust the speed of the prime mover to make the frequency the same;

Fourth, it is difficult to have the same phase angle. Therefore, rough synchronous parallel connection is generally adopted on ships, that is, a parallel reactor is connected in series between parallel generators. After the above conditions are met, when the synchronization index approaches zero, the parallel switch is closed and the two generators are connected together through the parallel reactor. At this time, the circulating current between the two generators is limited by the reactor, which synchronizes the two generators.