Study of a future metropolitan electric network adapted to introduction of cryogenic high‐power cables

The authors have investigated the operational feasibility of a future metropolitan electric power system associated with highly densified cryogenic cables. A new concept of power system configuration with cryogenic cables and its operation have been proposed. Three different models of future power transmission systems in large cities of Japan have been constructed as the background systems prior to introduction of cryogenic cables in the 21st century. This paper considers one of the three models which is characterized by its conventional transmission system constructed mainly by 154-kV transmission lines stepping down directly from the 500-kV outer ring without any intermediate voltage class. This paper also discusses whether or not the power system model will be operated effectively together with cryogenic cables to supply demands forecasted in the period subsequent to the first decade of the 21st century. The computer simulations are carried out to obtain power flow and bus voltage distributions for a peak load period as well as for an off-peak one in the power system model. These simulations reveal that the conventional background power system should be arranged very carefully before introducing the cryogenic cables to facilitate their operations. (1) On a contingent trip of a cryogenic cable in the peak in the peak load period, not all bus voltages are expected to be kept within a tolerant zone due to the high impedance of 154-kV conventional transmission lines in the power system model. (2) Thus it is proposed that the background conventional system prior to introduction of cryogenic cables should be developed not only by extension of 154-kV conventional transmission lines but also by introduction of 275-kV lines. (3) Bus voltage rises induced in the off-peak load period are reduced by effective utilization of 275-kV conventional transmission lines.