The whole process of putting the motor unit into parallel operation is called parallel operation. One generator set shall be operated first and the voltage shall be sent to the bus. After the other generator set is started, it shall be in parallel with the previous generator set. At the moment of closing, the generator set shall not have harmful impulse current and the rotating shaft shall not be suddenly impacted. After closing, the rotor shall be quickly pulled into synchronization. (i.e. the rotor speed is equal to the rated speed) therefore, the paralleling of generator sets must meet the following conditions:

1. The effective value and waveform of generator unit voltage must be the same;

2. The voltage phases of the two generators are the same;

3. The frequency of two generator sets is the same;

4. The phase sequence of the two generator sets is consistent.