Influence on transmission line relay protection under DFIG-based wind farm intergration

In conventional wind farm outgoing line protections, the fault characteristics of wind farms have been rarely considered and thus the protections may mal-operate or refusal-operation due to the integration of large-scale wind power. This paper analyzes fault characteristics of the outgoing transmission line from a DFIG-based wind farm with LVRT capability and indicates that the main frequency component of the wind farm side short-circuit current varies with the speed of wind turbine generators, while the main frequency component of the wind farm side bus voltage still maintains the power frequency during a non-bolted-three-phase fault in the outgoing transmission line. Performances of directional protection based on the positive sequence voltage and current power frequency, the distance element using the power frequency voltage current ratio to measure fault distance, and the fault-type element which uses the sequence current or phase current differential mutation quantity are affected severely, while zero sequence current protection is affected to some degrees. Performances of those two algorithms are analyzed and compared on the PSCAD/EMTDC platform.