Reactive Power

Negative real power simply means that power is flowing in the direction
opposite from convention. For a generator, it would mean that power is
flowing from the grid/bus into the generator to keep it spinning. This
happens when the engine/turbine is not generating enough power to
overcome friction/windage losses and the electrical bus has to supply
power into the generator to keep it spinning. (it does NOT mean the
generator shaft has reversed its direction of rotation)

Similarly, negative reactive power means reactive power is flowing in
the direction opposite from convention. Normally a generator supplies
reactive power to a bus to 'feed' the reactive loads on the bus.
Convention is that inductive loads consume 'positive reactive power' and
capacitive loads are said to supply 'positive reactive power'. You
could also argue that capacitive loads supply 'negative' reactive power
which cancels out the 'positive' reactive power of inductive loads.

For a generator, reactive power is usually labeled 'positive' when it is
over-excited and supplying reactive power to inductive loads. If
under-excited, it actually draws reactive power from an infinite bus
(its reactive power is 'negative').