A method for synchronizing and connecting a first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) with a second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) with an intelligent electronic device (280, 1110) by use of at least one switching device (250, 260, 730, 750, 810,920, 940, 1115) between the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) in an electrical power system, wherein the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) includes a voltage decaying in magnitude and frequency at a first rate of change (dV/dt, dφ/dt), the method comprising: a) monitoring power supply parameters for the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140); b) identifying at least one instance for operating the at least one switching device (250, 260, 730, 750, 810, 920, 940, 1115) using the monitored power supply parameters and selecting one instance to connect the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140), wherein identifying at least one instance includes a predicting magnitude of phase angle difference and voltage difference between the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140), based on the measured signal values and the first rate of change (V, dV/dt, f, φ and dφ/dt); c) having phase shifting and voltage magnitude correction in the electrical power system carried out in anticipation for synchronizing power supplies on connection of the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) with the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) at the selected one instance; and d) operating the switching device (250, 260, 730, 750, 810, 920, 940, 1115) to connect the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) in the electrical power system at the selected one instance for connection, wherein having phase shifting and voltage magnitude correction carried out in anticipation for synchronizing power supplies on connection of the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) with the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) at the selected one instance includes cross switching of one or more phases in the electrical power system, wherein cross switching of one or more phases in the electrical power system includes synchronizing phases A, B and C with phases B, C and A or phases C, A and B, and wherein the method further comprises: if the decay rates of the voltage and frequency are determined to be too fast for any of the above steps, wait for the voltage to drop below 30% to initiate closure of the switching device (250, 260, 730, 750, 810, 920, 940, 1115) at residual condition or after a fixed time. a) monitoring power supply parameters for the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140); b) identifying at least one instance for operating the at least one switching device (250, 260, 730, 750, 810, 920, 940, 1115) using the monitored power supply parameters and selecting one instance to connect the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140), wherein identifying at least one instance includes a predicting magnitude of phase angle difference and voltage difference between the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140), based on the measured signal values and the first rate of change (V, dV/dt, f, φ and dφ/dt); c) having phase shifting and voltage magnitude correction in the electrical power system carried out in anticipation for synchronizing power supplies on connection of the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) with the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) at the selected one instance; and d) operating the switching device (250, 260, 730, 750, 810, 920, 940, 1115) to connect the first sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) and the second sub power system (110, 120, 170, 710, 720, 905, 907, 1120, 1130, 1140) in the electrical power system at the selected one instance for connection,