Parallel Connection

One thing to keep in mind, is that both generators should have roughly the same droop (speed and voltage measured in % of capacity). Otherwise, as the load changes, one could assume more of the change than the other, and not share an equal % of its capacity with the other. And, that's not good. If a load drops off the line, one could reverse power the other. Or, if a large load is started, one could easily get overloaded. Also you need to ensure that you don't get oscillating currents between the two due to reactive load hunting from the voltage regulators. Both generators should run at the same % of their capacity to allow for proper sharing of loads when those loads change. Otherwise one or the other can trip on a fault before you can react to it and dump the whole load on the other. Then the other could be overloaded and trip also. You never really know when a load will come on line or drop off. You don't want one of them to be left carrying the whole starting current/load or get reverse powered from a load dump. Reactive currents could flow between the generators without even getting to the line. Voltage regulator settings are important. Make sure that reactive loads are also equally shared (%-of-capacity-wise). That way, load changes won't take you by surprise.

As far as the effect on the step up transformer goes, I don't think it really cares where it gets it power from, as long as it stays within spec.

Dear sir

thanks for your replay

Please, can I formulate the question in another way

what is the difference between connected tow generator before step up transformer

or after step transformer.and What is the best way between them and why

thanks

I have no idea. I never worked on/with such a system. Sorry.

Usually, step-up transfo is necessary because the generator(s) could not economically work at the higher voltage at its power rating.

Grid connections are 33/66/132 kilovolt or similar/more. Even generators of hundreds of Megawatt are not economic at 33 kV. There is a limit to the size of transmission cables which means that higher powers have to go to higher voltage for long distance.

Even if direct connection is feasible, it is usually the case that the amount of short circuit current at HV would wreck the generator for any fault. The transformer serves to limit the current from HV and isolate the generator, enabling effective protection against earth faults in generator stator windings.

The transfo also protects the Grid from the generator & it is unlikely Grid operator would agree to direct connection, since a fault on generator could affect other generator plant & customers.

I want to supplement to the cr4 member Rixter.

The load sharing depends upon the Prime Movers droop character also.

DHAYANANHDAN.S