Expansion-Oriented Design and Optimization of Medium-Voltage Collector Networks in Utility-Scale Wind Power Plants

The rapid growth of utility-scale wind power plants has increased the importance of medium-voltage (MV) collector-network design. While conventional collector systems are generally optimized for the initially installed generation capacity, future expansion opportunities, long-term operational flexibility, reliability requirements, and network scalability are frequently neglected during the early stages of design. Consequently, collector systems that are technically adequate during commissioning may become suboptimal during future capacity upgrades. This paper presents an expansion-oriented engineering methodology for the design and evaluation of MV collector networks in utility-scale wind farms. A 25 MW wind power plant, consisting of four 6.25 MW wind turbine generators connected through a 34.5 kV collector system and a 110 kV grid interconnection substation, is used as a case study. Manual engineering calculations based on IEC principles are combined with detailed power-system simulations and practical equipment selection studies. Short-circuit levels, load-flow performances, cable ampacity, voltage-drop characteristics, thermal withstand capability, collector topology alternatives, and future expansion scenarios are evaluated jointly. Unlike conventional studies focusing solely on grid compliance, the proposed methodology investigates collector-system development paths, including radial, open-loop, ring-network, and dual-transformer architectures. The results demonstrate that the collector-network topology has a significant influence on reliability, expandability, protection complexity, and long-term investment efficiency. Furthermore, manually derived engineering models are shown to provide highly accurate validation of detailed simulation studies and constitute a valuable tool for preliminary design assessment. The proposed approach provides a practical framework for future expandable wind farm developments and contributes to the optimization of collector-system planning from both technical and operational perspectives.