Warning: memory may be slightly variable on some points following - maybe
not.

> I mean, will the generator only contribute to the power grid, or will it
>
> work like a engine itself, if the (mechanical) energy is not strong
enough?
>
> On a DC system diodes take care of it.. but in the AC system?

The power station can progressively "put its shoulder to the load". You can
make voltage and no power and even run as a motor BUT usually you drive
energy into the alternator and it TRIES to accelerate the alternator and
instead phase shifts it ever so slightly and adds power. If the alternator
makes a significant percentage of the total network power available you can
start to influence the frequency or voltage but usually the network is
substantially more capable and any one alternator "gets in behind".  If
desired the alternator can be run out of phase with the network and make
 VARs* but no power, to balance net reactive imbalance. VARs cost $ to send
and make no power at the other end so killing them locally makes sense. It
may be economic to have a small power station for this purpose - eg a gas
turbine container unit installed in an industrial area. (* Gargoyle knows).


DC links driving AC converters to small locales where link energy is a large
% of total can cause major issues. Without adequate control the link can
become unstable and drive voltage and frequency to interesting values. Long
ago Sardinia (I think) (just maybe Sicily) had this issue when mainland
fed.

Re NZ DC link across Cook Strait (among the worlds most treacherous
waterways) - voltage AFAIR is 500 kV DC wrt ground and cable are run in +/-
pairs for 1 MV per pair. Memory may misserve - may be half that each. Still
'a lot of voltage'. Fishing boats are not overly welcome :-).



                       Russell
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