What protection is used for the 35kV busbar in a wind farm

35kV busbars in wind farms are typically protected using high-speed differential protection, overcurrent-based schemes, and optionally surge arresters or fault indicators for monitoring.

Busbar Protection Methods

For a 35kV busbar in a wind farm, protection is primarily designed to detect and isolate faults quickly to prevent equipment damage and maintain system stability. Common protection methods include:

• Differential Protection: High-speed differential relays are widely used for busbar protection. They compare currents entering and leaving the busbar and trip the associated breakers if a difference exceeds a set threshold, indicating an internal fault. This method provides fast fault clearing, which is critical for minimizing arc-flash hazards and protecting multiple connected feeders .
• Overcurrent-Based Protection: Overcurrent relays can be used in interlocking schemes or as part of a differential protection setup. These are simpler and cost-effective for distribution busbars where fault currents are lower and speed is less critical .
• High-Impedance or Percentage Differential Protection: These schemes are suitable when CT saturation or external fault conditions could compromise security. High-impedance differential relays force error currents back through the CTs, ensuring reliable operation during internal faults .

Equipment and Monitoring

In wind farm applications, 35kV busbars are often housed in cable branch boxes with prefabricated copper busbars. These devices may include:

• Live-line indicators to show energized circuits
• Fault indicators to detect short circuits
• Surge arresters to protect against transient overvoltages
• Fully insulated, sealed, and maintenance-free construction for outdoor or indoor installation

Digital and IEC 61850-Based Protection

Modern wind farms increasingly use digital busbar protection schemes based on IEC 61850 process bus standards. These systems employ:

• Merging Units (MUs) to collect current, voltage, and breaker status
• Central processing units to execute differential protection and breaker failure logic
• Interoperable architecture allowing integration with other network element protections This approach enhances speed, selectivity, and security, while reducing wiring complexity and enabling remote monitoring and control.

Summary

In summary, 35kV busbars in wind farms are protected using a combination of high-speed differential relays, overcurrent schemes, and optionally high-impedance differential protection, supported by monitoring devices like live-line and fault indicators. Modern implementations often leverage IEC 61850 digital protection for improved reliability, fast fault clearing, and integration with the wind farm's collector system .