Regarding Generator VAR Capability

We know that grid acts as a capacitive load at low loads and acts as inductive at high loads. when the VAR we are supplying to the grid is all the time is more i mean with lagging pf and positive reactive power in terms of setpint. i saw sometimes the setpoint we are giving 100 mvar and mixing all units some times its crossing 500 mvar whats my doubt is when we are supplying more var some times we are doing manual tap change of power transformer in local from 11 to 10 or from 10 to 9 like that..by doing so....what will be the effect on generator VAR Capability is it increases or what....by reducing the tap change on power transformenr hw its affecting the generator VAR capability still i didnt understand...can any one explain please