Abstract: To solve the long-standing problem of single-phase grounding fault treatment of the collector line in wind farm collector system, a flexible grounding mode of wind farm is proposed. The three-sequence equivalent circuit of flexible grounding wind farm and composite sequence network of single-phase grounding fault are derived. A novel method of flexible voltage arc suppression based on zero-sequence voltage flexible control is proposed, which can actively suppress the fault voltage and fault residual current to zero to realize reliable arc suppression. Furthermore, a high-resistance fault identification and protection method based on dynamic increment of zero-sequence current is proposed. The fault residual current is gradually amplified by regulating the zero-sequence current to realize the sensitive detection and protection of permanent grounding fault. A large-scale wind farm model with doubly-fed induction generator (DFIG) is established in PSCAD/EMTDC, the simulation results under various fault conditions show that the method can control the fault voltage of the collector line considering system unbalanced voltage. It realizes arc suppression of transient single-phase grounding fault, dynamically detects and suppresses the residual current of permanent grounding fault, and achieves protection of high-resistance grounding fault of the collector line. This technology is expected to improve the operation flexibility and fault defense ability of wind farm, and effectively guarantee the continuity and reliability of new energy power delivery.