French TSO operational voltage risk management in a volatile electrical environment

摘要

Due to the specific behaviour of the load integrating a large part of electrical heaters, the French power system has to face historically high peaks of load in particular in winter during low temperature periods. Moreover, the evolution of the European electrical energy context with the development of renewable energy, increase exchanges of electrical energy through market coupling, cross borders balancing offers and emergence of demand response mechanisms lead to globally optimized the system operation closer to real time, closer to its security limits and in a more and more volatile environment. This involves adapting operational methodologies and tools in order to take the right decision at the right time with regard to the available action levers. These considerations concern particularly the voltage control issues of the French transmission system. Indeed, RTE, the French TSO has to face: 1. Low voltage phenomena and voltage collapse risks in winter depending obviously on the global load level, but also on the electrical flow over-passing on the transmission system and on a growing amount of wind and photovoltaic energy sources which can relieve the system or increase the constraints with regard to their localisation and completely change the constraints typology with regard to the historic one's; 2. More constraining high voltage phenomena in low load periods due to the increase of renewable energy generation which decreases the global injection of the concerned areas, but also and more and more in intermediate or breaking periods during which system operators have to examine how to control the system in anticipation at both low and high voltage limits in order to activate, when necessary, the adapted available action levers. Based on feedback experience of earlier voltage collapses, and in order to ensure voltage control in accordance to the evolution of electrical energy environment, RTE developed dedicated 1. voltage study methodologies and tools to lead precise and robust analysis mostly based on dynamic simulations and risk analysis at each study time scale to characterize the phenomena, to calculate the limits of the system and propose operational criteria available to systems operators to take the right decisions from usual control means up to emergency orders if necessary. Equivalent methodologies and tools are also used for planning studies to justify and implement optimized long-term reactive power capacities to maintain the voltage within the limits; 2. operational procedures and processes to ensure in anticipation a right representation of the system situations using the best predictive and actualized hypothesis and a closed coordination between regional and national RTE control centres as well as with the neighbouring TSO or adjustment actors in particular concerning the short term analysis; 3. dedicated automatisms to regulate the voltage in normal situation or to ensure the voltage security as a defence plan in case of non predicable event or over sizing situations to avoid voltage collapse which could lead to unacceptable consequences for the European system. This article will provide an overview of the French TSO operational voltage control framework illustrated thanks to experienced situations and descriptions of the methodologies and analysis tools, operational processes and automatisms presented above and main benefits resulting of this global scheme.