Systematic Evaluation of Renewable and Thermal Generation Integration into a 69 kV Subtransmission Network Using DIgSILENT PowerFactory: A Case Study of CENTROSUR (Ecuador)

The Ecuadorian electrical system, with a generation mix dominated by hydroelectricity, experienced prolonged rationing during recent droughts, prompting a search for generation options that can be installed near consumption centers. Before authorizing new connections, it is necessary to determine the capacity of the subtransmission network for distributed generation and whether this limit depends on the installed technology. This study addresses the integration of renewable energy systems into the 69 kV network of the Centro-Sur Regional Electric Company (CENTROSUR, Ecuador). Hourly wind and photovoltaic energy profiles were considered at eight candidate busbars, and the coordinated integration capacity of the system was determined by simultaneously injecting power into all of them. Six configurations with equal incoming power (renewable, thermal, and three mixed) are compared using power flows, N-1 contingencies, short-circuit analysis (using the full method), and RMS transient stability analysis with the support of the DIgSILENT PowerFactory tool. Five operating points are analyzed: two full dispatch points and three extracted from the year’s chronological data based on hourly solar and wind resource availability. The overall results show that the limit is set by a shared export corridor, not the bus connection point. The coordinated capacity is 160 MW at peak demand and 60 MW at minimum demand, compared to the 620 MW and 380 MW, respectively, that would result from adding the individual capacities of each bus. The operating point governing incoming power is the export condition, which occurs during an hour of intermediate demand with high local generation, not during peak or minimum demand. The sizing procedure is potentially applicable to other meshed subtransmission networks fed from a few points of the transmission system, a situation that can be replicated in other parts of the world.