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What is the wind turbine protection?
The wind turbine must comply with the "Technical Regulations for Wind Farms Connecting to the Power Grid" issued by the State Grid Corporation of China. Specifically, if the voltage at the grid-connection point (the node or busbar on the high-voltage side of the wind farm's step-up transformer) drops to 20% of its rated voltage, the turbine must remain operational for at least 625 milliseconds without disconnecting from the grid. Additionally, within 2 seconds following the voltage dip, the turbine should recover to 90% of the rated voltage, ensuring uninterrupted operation.
Frequency protection is crucial for wind turbines as well. This mechanism is designed to quickly isolate the turbine when grid frequency fluctuations exceed safe thresholds. Excessive frequency variations can harm the turbine’s normal operation. If the grid frequency surpasses the upper limit (typically 50.5 Hz) or falls below the lower limit (49.5 Hz), the over-frequency protection triggers immediately, cutting off the turbine. The response time for such protection is generally less than or equal to 100 milliseconds.
Current protection is another essential feature, including quick-break protection and over-current protection to safeguard against excessive current. Additional protections include three-phase current and voltage imbalance detection, temperature rise monitoring, speed monitoring, vibration alarms, and cable twist prevention.
For variable-speed constant-frequency turbines, the converter plays a critical role in achieving decoupled vector control. Most modern wind farms utilize doubly-fed induction generators. During normal grid connection, the stator voltage operates at 690V AC. However, during grid faults, the voltage may drop significantly. In such scenarios, the stator flux linkage risks losing synchronization with the terminal voltage. To prevent overvoltage and overcurrent issues, protective measures are implemented.
Crowbar protection is commonly employed in converters for doubly-fed wind turbines. Key parameters monitored by this system include DC link overvoltage, overcurrent in the grid-side converter branch, and rotor overcurrent. These safeguards ensure reliable and safe operation under various grid conditions.
In summary, wind turbines must meet stringent technical standards while incorporating advanced protection mechanisms to maintain stability and safety during both normal and fault conditions.