Islanding protection system with active and reactive power balancing control for Tokyo Metropolitan power system and actual operational experiences

The Metropolitan power system owned and operated by Tokyo Electric Power Company consists of several radial sub-power systems. Each sub-power system receives electric power from the 500 kV mesh bulk power system, via 275 kV parallel overhead transmission lines and three 275 kV underground cables circuits which take the same route. These subpower systems cannot be interconnected to one another due to the restrictions imposed by short-circuit fault current. One of these metropolitan power systems supplies many politically and economically important loads and the load capacity of the locally installed power plant is small. Most of the indigenous load is supplied from the bulk 500 kV power system via the parallel 275 kV tie transmission lines. This metropolitan system consists entirely of 275 kV, 154 kV and 66 kV underground cables. If the power supply from the bulk 500 kV power system is interrupted by a fault on the tie transmission line, the metropolitan power system will be separated as a heavily overload system with large shunt capacitance. The authors have therefore installed an islanding protection system with active and reactive power balance control functionality to protect the most important loads in the metropolitan area from serious black out