Possible logics of reactive power injection or absorption in HV grid for TSO: case study of a wind farm

In the last few decades, the penetration of renewable energy sources in the scenario of the electricity production has strongly increased and it is expected to continue. The electricity generation is becoming more and more distributed rather than centralized and this made necessary to leave the old services for control and regulation and move towards more distributed strategies. For this purpose, Terna, the national Italian TSO, has launched a call to extend the voltage regulation service to a larger number of resources. The project is called “Progetto Pilota per la regolazione di Tensione” and it aims to verify the reliability and effectiveness in providing the voltage regulation service by the plants. This study aims to regulate the provision of reactive power for voltage regulation purposes by the wind farm of Portoscuso, owned by Enel Green Power. The Portoscuso wind farm is located along the southwestern coast of Sardinia, within the national site of interest Sulcis-Iglesiente-Guspinese. It is the largest wind farm of Enel Green Power in Italy, featuring 39 turbines each with a capacity of 2.3 MW and a total capacity of approximately 90 MW (89.7 MW). Portoscuso wind farm participates in Terna's pilot project for the provision of voltage regulation service. This document briefly introduces the regulatory context and the technical rules for participating in the project, paying particular attention to the minimum requirements that the plant must meet. Subsequently, the availability of reactive power from the plant is evaluated during days by means of the capability curve of each turbine. The capability curve of a turbine says how much reactive power the turbine can provide to the network in certain conditions of active power production and for certain voltage levels. For each turbine, the capability curve is reconstructed, and simulations have been run over time to verify that it can provide the required reactive power. Since the Portoscuso grid has a radial structure with a single power supply network, the calculation of the active and reactive power flows has been realized by applying the Backward Forward Sweep method (BFS), which is an iterative method of radial powerflow to calculate voltage on nodes and current along the branches of the network. The reactive power injection by the wind farm into the HV grid can be performed following different logics of distribution among the wind generators. In this study different logics have been tested by means of simulations and then compared. For every distribution logic it has been verified that the plant meets the minimum requirements of reactive power and the total amount of energy lost due to the Joule Effect has been calculated, to evaluate the effectiveness of the logic itself. The goal of this analysis is to verify that the plant is effectively able to provide the reactive power necessary for the voltage regulation purpose and additionally to find the reactive power distribution logic that minimizes the costs in terms of energy loss. Every simulation has been developed and run in Matlab, a numerical computing and programming platform.