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The outputsof the Alternators have to have the same voltage, frequency and phase rotation, if it is a3 phase supply. They have to be matched.
There is adevice called synocroscope product of seg (german company) connected to two generator outputs it pointed12 oclock when the freq. & the volt. & the seq. is right & can make contact at this cndition.
To synchronize , several important factors must be checked.
1. The phase rotation of both alternators must be the same.
2. The AC voltages of both alternators should be equal.
3. The frequencies of the on-coming alternators must match when synchronized.
In an alternating current electric power system, synchronization is the process of matching the speed and frequency of a generator or other source to a running network. An AC generator cannot deliver power to an electrical grid unless it is running at the same frequency as the network. If two segments of a grid are disconnected, they cannot exchange AC power again until they are brought back into exact synchronization.
A DC generator can be connected to a power network by adjusting its open-circuit terminal voltage to match the network voltage by either adjusting its speed or its field excitation; the exact engine speed is not critical. However, an AC machine must match both the amplitude and the timing of the network voltage, which requires both speed and excitation to be systematically controlled for synchronization. This extra complexity was one of the arguments against AC operation during the War of Currents in the1880s. In modern systems, synchronization of generators is carried out by automatic systems.
Besides what have been said on this subject so far, one important thing is to insure proper or perfictly proportional reactive power sharing through proper adjustment of voltage droop (in case the load sharing device has no voltage droop control - which is the case so often). As, when an alternator runs at a lower power factor the excitation system could be damaged.
Load sharing by each alternator must be proportional with respect to capacity of each alternator orelse the largest alternator would try to supply the whole load whilst other alternators will run on no-load, creating unbalanced alternator loading. It is also wise to choose alternators of same capacity for load sharing balance.
You should have a synchronizing panel. to make same frequency.
The purpose of synchronizing two generators is to share the load, it requires the same voltage, same phase sequence and phase within one another and to the grid, so there are no circulation currents from one generator to the other and from the grid to generators.
To sync2 alternators it must fall in below conditions:
1)same voltage level
2)same phase sequence
3)same phase angle
first priority that more than2 engines load share level same. If load capicty low then engine should be revrsepower and shutdown activated. when load run on engine both engines frequency and voltage level same and maintained if these parameters changed the one of engine should take load from other and overload.
Speed, frequency, phase............................................
