There are three cases on board usually needs and truck operators. First, the need to meet the needs of network load, when the single load up to 80% of rated capacity, and the load may increase, then we should consider another parallel generators; Second, when out of the harbor by a narrow channel from the dock or out When state and other motorized sailing, sailing ship for safety, need two generators in parallel operation; Third, when you run the backup power supply unit need to replace the unit under, in order to ensure uninterrupted power supply, and the need to replace the car.

Quasi-synchronous mode and the car and the car is a method commonly used in the current ship. To make the parallel operation of AC synchronous generator steady work, each parallel operation of generators following conditions must be met:

(1) Subject to the unit and the phase sequence and operation of the unit (or grid) of the phase sequence;

(2) Subject to the unit's voltage and operation of the unit (or grid) voltage equal size;

The early phase (3) Subject to the early phase of the operation of the unit and the unit voltage (or power) voltage is the same;

Equality (4) Subject to the unit voltage and frequency of operation of the unit (or grid) voltage frequency size.

Since the installation of the generator has been set on the phase sequence of the phase sequence generator and the grid was measured to ensure that the conditions of phase sequence. And therefore the operation is to detect and adjust the car to be and generators voltage, frequency and phase, so as to satisfy the above three conditions moment by closing the main switch the generator into the grid. This ensures that there is no rush current at the time of closing and the car, and the car can maintain a stable and synchronous operation.

Actual and car, in addition to the phase sequence, the other conditions can not be exactly the same, but there must be a certain frequency difference only 'can be quickly put into parallel operation.

First, when the frequency is equal to the initial phase of the same, when the voltage is not equal, and the two generators will produce a car instantly reactive nature of the circulation between the two units, played on two generators equalizing effect. Since the generator and the equivalent of a small car appear instantly reactance, so when the voltage difference is large, the closing moments will have a huge impact on current and power systems for the two generators are unfavorable. The impact of electric power generated by the huge impact of current will damage the generator armature windings, main switch contact, so the bus deformation. General and vehicle operation, the voltage difference △ Diao Tun exceed 10% of the rated voltage.

Second, to be with the operation of the unit and the unit is equal to the voltage and frequency are equal, but different initial phase, two generators and vehicles to be instantly at the main switch and the machine moving, there will be a static contact between the voltage difference between the two units will be Circulation 90 ℃ hysteresis voltage difference, in which case the circulation of reactive power is no longer pure nature. The circulation of active and reactive decomposition, circulation and circulation active component reactive component, in the role of active circulation, one into another gear and accelerated, eventually making the parallel operation of two generators to achieve the same phase synchronous operation. Circulation of the active component corresponding power called full step power, where full step ahead of the generator output power, lagging power generators to absorb the whole step. Whole step whole step corresponding torque power for the purposes of a resistive torque generator ahead, make speed down, for the purposes of the lag generator is driven torque, the speed increases, the two machines will eventually be pulled into the same phase synchronous operation . This process is called "pull-in" process. Reactive nature of the circulation of the two generators play equalizing effect. In order to reduce the impact of current, general and vehicle operating requirements phase difference is less than △ S150.

Third, and the machine running the machine until the voltage is equal to the initial phase of the same, but the frequency is not equal, and when the car. In the closing moments of the voltage difference does not appear, there is no circulation.But because the frequency is not equal, with the time shift, there will be a phase difference, as long as the phase difference appeared, on the consequent circulation, appears full step torque, while the other one gear acceleration. As long as the frequency difference is not ultimately rely on full step torque can "pull in sync." If the frequency difference △ f is too large, often difficult to pull into synchronization, while also increasing the circulation after the closing of the generator and electrical systems are negative, this situation should be avoided. Usually when the car operating requirements and the frequency difference △ f less than 0.5 Hz, to 0.25 Hz best.

Generators and car, closing moments either condition is not met, the group will have an impact between the generator current. The impact of current reactive component from equalizing effect; impact torque generated from the active component full step effect. As long as the impact of current small, and truck operators on favorable. If the inrush current is too large, it will cause the car to fail and, in severe cases can result in the ship power outages, and even cause damage to the generator set.