Before Synchronization — Generator Mode

Droop and isochronous are modes of the governor of the engine driving the generator. If you increase the load on the generator, the mechanical load on the engine increases. In Droop, the engine will slow down, in isochronous it will still maintain a constant speed if possible.

When you parallel a generator with an existing bus, you increase the engine speed until the frequencies and phases of the generator and bus match. The generator's engine should be in droop mode. Once it is paralleled (connected), the generator's throttle is increased so that it assumes part of the load.

I hope this helps to answer your question.

No need to go to isochronous governor unless you are the only or ideally the largest machine on the system.

Before synchronizing, the generator has no load, so there is no droop. Your speed/load control can be used to match frequency.

Once you parallel, you add speed so you pick up load, and your droop starts working.

It will be dependent on the size or capacity of each generators that are going to be connected together..

If you expecting frequent load variations, I would suggest to use the Droop method especially if both generators are specification-wise identical.. The operating frequency settings for each would be a bit different, thus creating an upper and lower frequency operating limits that is acceptable during any load variations..

Otherwise use the Isochronous method where you set both generators to one identical operating frequency.... advisable only if you have a stable electrical loads..