System Strength Reduction in an Island Grid Through Transitioning to 100% IBR

Puerto Rico is an island that is heavily dependent on fossil fuels for base electricity generation. Chronic lack of preventative maintenance has also taken a toll on the available generation mix which occasionally is not available to meet the entire load demand. The reality of Puerto Rico is reflected in media coverage such as the Department of Energy PR100 study, which will lay down the pathways and roadmap to lead Puerto Rico into 100% renewable generation as not only to reduce dependency on fossil fuels, but also as an alternative to replace the existing obsolete conventional plants. One of the challenges to face when connecting inverter-interfaced renewable generation to the grid is the fact these resources cannot provide the amounts of short-circuit levels that are commonly provided by rotational synchronous generation. With this transition, it is not simple to determine if the power system can be protected with existing protection schemes or, to understand what protection settings updates or protection philosophy upgrades may be required, as well as the extent of this required upgrade. To address this challenge, this paper assesses the system strength at various stages of utility scale renewable shares in an island system. It identifies the reduction in short circuit currents for both three phase faults and single line to ground faults as conventional plants are removed from the instantaneous generation mix to give place to inverter-based resources. This research provided the transmission operator with better insight on the extent of required system modifications to ensure a robust and safe grid.