If the system frequency is 50 Hz., then the speed for a 4 pole generator should be 1500 rpm. It seems the frequency of your generator is 1566.67 rpm(and not 2566.67rpm -- please check the input to the display unit) corresponding to the electrical frequency of 52.2235 Hz. This generator can be definitely synchronized with the system of 50 Hz. by reducing the speed of the generator. A normal synchronization is possible.