Wind farm collector protection using directional overcurrent elements

The protection of wind farm collector circuits is complicated by high generator output, long runs of cable, a variety of cable sizes, wind turbine step-up transformer inrush, and a variety of wind turbine technologies. Non-directional overcurrent protection often does not provide the necessary sensitivity for detecting faults on remote points of the circuit or backup protection for wind turbine step-up transformers. This issue is further complicated when attempting to mitigate arc flash incident energies. Directional elements are necessary to set overcurrent pickups below maximum generation levels. Setting the directional element by traditional means may result in a reliability risk at varying generation VAR outputs. Using event reports collected by relays, this paper demonstrates the limitation of non-directional overcurrent protection on wind farm collector circuits, and the pitfalls of an improperly configured directional element. A unique solution using directional overcurrent elements further secured by a load encroachment function can be used to solve these problems. Field data verifies the security of the application over a wide range of operating conditions.