Q.What would happen with the 3 phase generator, if we use only single phase for load serving while the remaining phase will be open?

 Using a three phase Generator for Load is sufficient way to provide power to balanced and unbalanced loads.However,if one phase goes out , more current and voltage will be drawn to the other phase. this will cause the motor to heat . in Case one phase is just out , the motor will over drawn current and voltages which will result in over heat of the motor and eventually the motor will burn out.