Abstract: The traditional line capacity expansion method suffers from the low overall utilization rate of lines and poor power support ability during a contingency when facing seasonal short-term peak loads. Therefore, with the function virtualization as the core concept, this paper studies the functional architecture of virtual distribution feeders that integrate traditional distribution feeders with energy storage components. By using paired energy storage components to construct a virtual power transmission channel, the virtual distribution feeders address seasonal short-term peak loads, delay the conventional line capacity expansion project, and provide emergency power support and auxiliary service functions during non-peak periods to improve the overall utilization rate of energy storage components. In order to further fulfill the flexible transmission and emergency power support potential of virtual distribution feeders, an optimal configuration model for line capacity expansion in distribution network is proposed to optimize the energy storage configuration for virtual distribution feeders while ensuring economy feasibility and meeting peak load demand. Case studies show that the virtual distribution feeders can effectively delay the traditional capacity expansion projects and cope with the seasonal short-term peak loads. For areas with relatively stable load growth, or long lines and short designed delay years for capacity expansion, the advantages of virtual distribution feeders are more noticeable.