DC technology for stable and reliable grids

The expansion of cities often leads to enlarged load concentration and carries extra challenges to managing the electrical grid while insuring power availability to critical loads. The developing Shanghai power grid faces many challenges in the areas of generation, transmission, and distribution of the rapidly growing amounts of electrical energy in demand. Its development should address issues of congestion, voltage-stability, power restriction, permits, and scarcity of land or right of way. In this paper, an equivalent model of Shanghai power grid is implemented using the ABB power transient software analyzer (SIMPOW) where detailed modeling of the generators including exciters and governors is performed. Solutions including Fault Current Limiters (FCL), Static Var Compensators Light (SVC-Light®) and High Voltage Direct Current (HVDC) systems were analyzed to assess their effectiveness in addressing the grid issues stated above. The best solution was obtained when the individual AC subsystems were decoupled so a fault in a given subsystem is not propagated to another subsystem and short-circuit currents are limited only by local generation capacity. This solution was obtained using a DC ring where power sources and loads are connected to a common DC bus through Voltage Source Converters (VSC).