What are Practical conditions for MAXIMUM POWER TRANSFER  during Grid Synchronization.

As you are aware, when synchronizing two systems together, phasing, speed, rotation and matching voltages are the primary objectives. Once the two systems are connected and stable, the condition for maximum power transfer is when the power equation is a maximum:

P(d) = |Vs||Vr|/X*sin(d)

where,
Vs and Vr are the sending and receiving end voltages, and
X is the equivalent system reactance connnecting the two systems.

Thus, maximum power transfer occurs when sin(d) is a maximum with an angle of d=90 degrees. This is a theoretical operating point which brings the two systems to the edge of steady-state stability. In practical operations, allowances must be made for system dynamic excursions and stability safety margin which can only be determined by the utility operations authority.

i think i didn't completly get your question, but if you mean two grids synchronized together by a link, the AGC with monitoring relay on the link can control the amount and the direction of the transfered power on both sides.

practically for maximizing the power transfer, we cannot alter much with delta, but yes, the effective reactance can be lowered and the Xl in the equation P=EV*sin(delta)/Xl, if it is halved using FACTS compensators, the power transfer can be maximized, but this happens after synchronization.

For all practical purpose,the angle delta must not excced 30 degree in order to maintain
stability under all operating conditions including fault & other system disturbances.

Subrata is correct, normal generator opearating angle is low at maximum capability within the power transfer curve, this is due to maintain stabilty during transmission line faults. Therefore a dynamic study is required for these conditions.

Power transfer curve can be change via building of parallel line, installation of series capacitors in effect reducing X as noted above.

So max power is limited by generator capacity and the lines power transfer limits.

Mr Raymond and Mr Somesh are correct