Analyzing the boundaries for TSO-DSO coordination when activating flexibility for DSO´s in networks with an expected significant load increase

The Transmission System Operators (TSO) and Distribution System Operators (DSO) coordination literature deals with different coordination schemes or coordination methodologies. However, consumer actions or regular DSO operations continuously affect the system balance operation, and no major coordination is required as these actions individually have negligible impacts on the overall system. The literature has not previously analysed where the limit beyond which coordination is necessary. This question requires an analysis of the DSO operations where the need for coordination is foreseen and a case-by-case study of what type of impacts are created by the activation of the DSO flexibility resources on the responsibilities of the TSO. Such analysis helps to define thresholds and scenarios considering existing changes in distribution networks, which can be a reference for delimitating costly coordination procedures. This paper presents a revision of all the possible scenarios of the DSO operation needs and their impacts on TSO responsibilities considering the possible TSO/DSO borders at different voltage levels. Afterward, a methodology is proposed to analyse more deeply the impact of flexibility activation with an expected significant load increase. Representative case studies evaluate the possible impacts on TSO responsibilities of local flexibility activation. This paper concludes that the impact of local flexibility is expected to be significant when large power changes are managed in the short term, estimated in more than 50 MW if the DSO operates in 132 kV or more than 15 MW if the DSO operates up to 66 kV. At LV or MV level, minor coordination would be needed.