In Forward Synchronization, the voltage, frequency and phase angle of the incoming generator is synchronized to match the values of the bus bar. This is generally used when a generator needs to be synchronized with an already charged bus bar. as shown in the diagram.
Reverse Synchronization or backward synchronization is generally done when a the supply from a grid utility is needed to be synchronized with a bus bar in the factory. Since, it is not possible to alter the voltage, frequency, etc. of the incomer, in this case, the grid. The voltage, frequency, etc. of the bus bar are adjusted to match the incomer. (See drawing).
Synchronization of AC Sources
Instruments used in Synchronization