Volt/var Chain Process*

Abstract

Simplicity is the ultimate sophistication.-Leonardo da Vinci IntroductionPhysically, the voltage is a local quantity that differs in each node of the electricity grid, as it varies along with the power transfer and the characteristics of the grid. Due to their strong coupling, the reactive power has always been used to control the voltage in transmission grids, originating the term Volt/varprocess. Reactive power is produced and consumed by diverse appliances distributed throughout the power system and operated by different stakeholders, making Volt/var control an extremely complex issue by its very nature. The overall control strategy should be designed with special care to reduce the complexity of the resulting Volt/var chain to facilitate the management.Volt/var management is one of the most fundamental power system processes that enables the reliable and efficient operation of the electricity grids. It is used to ensure compliance to voltage limits and to keep the power factor close to one. Both the elimination of voltage limit violations and the minimisation of the reactive power flows extend the active power transfer capability of the grid. In other words, an appropriate Volt/var control increases the utilisation of the electrical infrastructure, thus lowering the need for grid reinforcement.The massive connection of renewable and distributed generation and the electrification of other sectors gave rise to new challenges and opportunities that call for an adaption of the traditional Volt/var control schemes. Deteriorated power quality and uncontrolled interactions between the systems operated by different stakeholders are recognised as the main problems to be solved by future smart grids [66]. Meanwhile, the ability of distributed energy resources to participate in the Volt/var process