Figure 2 displays the impact of wind farms integrated into the electric networks, depending on the time horizon and width of the area considered in the analyses [9, 10]. The time scales utilized in the impact studies of the wind farms on the electrical networks lead to a variety of the proposed models. These impact studies evaluated the following technical problems depending on the width of the area: reserve/regulating power (time/minute to half an hour), efficiency/unit commitment (time/hours to days) associated with the wind power forecasting, adequacy of power (having years as the time horizon), adequacy of the transmission networks (time/hours to years), grid stability (time/seconds to minutes), voltage management (time/seconds to minutes), and power quality (time/milliseconds to minutes). The paper focuses on voltage management, particularly voltage control in the electric networks with wind farms connected, proposing an original centralized control methodology (integrated into the Optimal Power Flow (OPF) module of the SCADA master system from the Central Dispatch) of the on-load tap changers (OLTC) corresponding to the transformers from the electric substations. SCADA is an acronym associated with Supervisory Control and Data Acquisition. Regarding the SCADA master system from the Central Dispatch of the DNOs or TSOs, it performs centralized monitoring and control for the electric networks over long-distance communications networks, including monitoring alarms and processing status data [11]. The main components refer to a central computer, operator interfaces, mass data storage, control software, and integrated communication networks. At the local level of the electric substations, there are peripherals suitable for  
Figure 2: The impacts of wind farms integrated into the electric networks, divided into different time scales and width of the area relevant for the analyses. real-time supervisory and control. In the control room of each substation, the system contains at least a Remote Terminal Unit (RTU), Station Master, having the functions of a data concentrator, real-time data server, and communication server. The SCADA system of the wind farms allows complete remote control and supervision of the entire wind farm and the individual wind turbines [12]. This works like a brain, connecting the individual turbines, the electric substation, and meteorological stations to a central data concentrator, CDC (master computer), which, together with a high communication network, enables the DM to supervise the behavior of all the wind turbines and, also, the wind farm [13]. The sensors for wind speed, wind direction, shaft rotation speed, and numerous other factors take over and communicate data to the CDC [14]. It will record in the database all the activity (with various sampling steps, 5 to 60 min, depending on the programming) and allows the operator to decide what corrective action (if it is necessary) is required to maximize the injected power [15]. Under these conditions, the changes in wind generation are managed within the SCADA system. Towards the central master SCADA system of the DNO or TSO, the injected power, daily energy, availability, and error signals are sent at equal time intervals (equal to the sampling step) [13; 15], serving as the basis for the real-time OPF calculations based on the proposed coordinated control methodology. The assumptions considered by the authors to integrate the proposed methodology in the OPF module referred to the use of the data uploaded from the SCADA systems implemented in the electric substations and the wind farms. These data from the two SCADA systems are transmitted through a wide-area communication network with high-speed data transmission in real-time to the SCADA master system from the Central Dispatch.