Wind Power Relay Protection Scheme

Wind power relay protection schemes are designed to safeguard wind electric plants by coordinating overcurrent, directional, and backup relays across turbines, collector systems, and substations to ensure reliable fault clearance.

Overview of Wind Electric Plant Protection

Wind electric plants (WEPs) consist of numerous wind turbine generators (WTGs) distributed over a wide area, connected via a collector system to a collector substation, which then steps up voltage to the transmission level at the point of interconnection (POI) . Unlike conventional power plants with a few large generators, WEPs have many smaller units, making relay protection coordination more complex . Protection schemes must account for the unique characteristics of wind generation, including variable fault current contributions, inverter interfaces, and low negative sequence currents .

Key Components of Relay Protection

1. Collector System Protection Collector feeders, which can be radial or networked, are protected using overcurrent relays. Settings are chosen to detect faults while avoiding misoperation due to combined WTG output or transformer inrush currents . Directional elements (e.g., 67PT, 67PI) provide backup protection for individual WTGs and ensure coordination with expulsion fuses at generator step-up (GSU) transformers .
2. Substation and Transformer Protection Protection covers GSU transformers, main station transformers, collector substation buses, reactors, and capacitors. Relays are coordinated to clear faults quickly while maintaining system stability. Ground and phase overcurrent relays (51G, 50G, 51P, 50P) are commonly used, with settings adjusted for the low fault current contribution from wind turbines .
3. Directional and Backup Relays Directional supervision is critical due to variability in wind generation. Relays must be carefully set to avoid misoperation caused by changes in generator VAR output or low fault currents. Backup non-directional relays may be required to protect against loss of polarizing voltage .

Relay Coordination Practices

• Overcurrent Relay Coordination: Relays are set to clear faults at the shortest possible time while coordinating with upstream and downstream devices. This includes adjusting pickup currents and time delays to match the characteristics of WTGs and collector feeders .
• Simulation-Based Design: Tools like MATLAB/Simulink are used to model wind farms and optimize relay settings, ensuring proper coordination and sensitivity for both phase and ground faults .
• Sequence Considerations: Positive, negative, and zero sequence currents are analyzed to determine appropriate relay settings, as wind farms often contribute low negative sequence currents and variable zero sequence currents depending on transformer connections .

Design Considerations

• Collector System Layout: Radial or daisy-chain configurations are common, with underground or overhead cables delivering power from WTGs to the collector substation .
• Fault Current Characteristics: Low and variable fault currents from WTGs require careful relay setting to avoid misoperation while ensuring sensitive protection for smaller conductors at the end of feeders .
• Coordination with Expulsion Fuses: Relays are coordinated with fuses at GSU transformers to provide selective protection and prevent unnecessary tripping of multiple turbines .

Conclusion

A wind power relay protection scheme integrates overcurrent, directional, and backup relays across WTGs, collector systems, and substations. Proper design ensures rapid fault clearance, system reliability, and coordination with protective devices like expulsion fuses. Simulation tools and careful analysis of fault current contributions, sequence components, and system layout are essential for effective protection of modern wind electric plants .