The reason why the generator will send back when it is just started (scientifically speaking, when the generator is connected to the grid) is because the current frequency and phase sequence of your generator and the grid are very close, but it is still not 100% synchronous.
So in order to make him better synchronized, he usually connects a resistor or other equipment first, and then passes a sampling current in the winding to achieve synchronization. After synchronization, remove the resistance and directly connect to the grid for power generation.
However, these problems do not exist in stand-alone computers. However, when many people are connected to the power grid, they have already replaced the resistor with something else. I'm just saying here. Now the grid connection has been automated for a long time, so there is no need for such trouble at all.
Generators, if they work alone, don't have these problems at all, such as the generator of your car, the generator of your motorcycle, and some small spare generators in the store. They work alone. Do you need to call back?
So, your problem is actually because there is little feedback during the synchronization process.
In addition, as long as the generator is driven by an external force (such as a water turbine or a windmill), cutting off the magnetic induction line will generate electricity and generate electricity.
He doesn't need electricity to start him.
But as for the excitation part, if the generator is empty, assuming there is no magnetic field and remanence, then the external power supply can be batteries or some permanent magnet generators.
Then after magnetizing the winding for a few minutes, some parts of the excitation winding will have remanence, so that when he rotates, he cuts the magnetic induction line to get a little current, then gives the excitation winding a stronger magnetic field, and then carries on the next process, a little stronger each time, so that the voltage is finally established and power can be generated.
This process of establishing voltage is actually very short, even if it is longer, it will not exceed 10 minutes.