Considerations for dynamic transfer of renewable generation between Balancing areas

Energy transactions between Balancing Authorities (BAs) on shared interties are typically scheduled as “Static” transfers that are fixed for the hour and ramped up or down only during a set 20-minute period at the top of the hour. Faced with increasing amounts of intermittent generation, many BAs are evaluating other means of adding flexibility to transactions, such as dynamic transfer. One concern associated with dynamic transfer is that the variation in line flows due to wind and solar variations could cause transformer taps and capacitors to cycle in response to the changing voltage. Another concern is the impact of dynamic transfers on power systems dynamic behavior. This paper reports on a recent study to explore the impact of dynamic transfer across CAISO interfaces on the steady-state voltage changes at key substations and the oscillatory performance of the system. This study involved a combination of statistical analysis, loadflow and dynamic simulation. The study showed that no additional limits are required on dynamically scheduled variable generation when the existing limits are applied to each interface.