Flexible Utilization of Transmission Grid Capacity for Wind Power Integration.

Abstract

Power systems around the globe face increasing shares of renewable energy sources, whose variable and stochastic nature calls on grid operators to rethink their approach to system planning and operation. Attaining the best trade-off between security of supply and operational costs under uncertainty is closely tied to a flexible utilization of transmission systems, defined as the ability to withstand unexpected variations of power on different timescales. This thesis investigates novel solutions in this regard and proposes original decision-making support-tools that favour the large-scale integration of wind power. Grid operators around the world are constantly under pressure, as the rate at which new generation capacity is connected to the system outpaces their ability to upgrade it with traditional grid expansion projects, such as the construction of new overhead lines. To this end, recent advances in the field of wide-area monitoring suggest how additional network capacity can be revealed in the existing systems by assessing the thermal state of critical components in real-time. Known as dynamic thermal rating, this novel approach is listed as a promising solution, although several challenges lay ahead. While dynamic thermal rating indicates that a significant margin for higher power flows is possible, accessing this potential requires innovative solutions in the operational horizon to limit the impact of the associated weather-dependent uncertainty. Novel analytical tools presented in this thesis let grid operators take advantage of this technical solution, by proposing revisited thermal models of components and accounting for common risk-aversion levels in the allocation of transmission capacity for day-ahead energy markets. Simulation results show that significant savings can be achieved in wind-dominated power systems by allowing higher power flows, without compromising on the high standards of security of supply, which grid operators must adhere to. Additionally, key contributions show that the full potential of this approach can be maximised by applying the core physical methodology of dynamic thermal rating not only to overhead lines, but to other components as well, such as power transformers. Contributions presented in this thesis further elaborate how a flexible utilization of transmission systems can also be achieved by focusing on operational aspects rather than novel infrastructural functionalities. The need for higher power flows can be anticipated by pre-positioning operating reserves while accounting for network limitations in a way that current sizing practices have not considered so far. An original perspective on the definition of zonal reserve capacity markets is offered in this thesis, which closely approximates ideal solutions while being compatible with fundamental properties of current electricity market structures. Overall, the results indicate that the successful integration of large-scale wind power generationwould greatly benefit from enhanced transmission system flexibility, and that increased awareness of natural phenomena and extensive cross-border cooperation would be needed to achieve it.