There are three types of protection philosophy for offshore wind farms which will ensure the reliable operation of the wind farm and the connected network.
- System Level Protection Philosophy
- Segment/Zone Level Protection Philosophy
- Component Level Protection Philosophy
IEC standard 61400-3-1 outlines the design requirements for fixed offshore wind turbine generators (WTGs), emphasising the need for redundancy in the electrical infrastructure to ensure reliability and prevent total shutdowns during faults. These documents, along with other relevant literature, are the key to design a reliable protection philosophy for all three levels as enlisted above.
Protection Philosophy for Offshore Wind Farms
System Level Protection Philosophy
System-level protection philosophy for an offshore wind farm involves a comprehensive approach to ensure the safety, reliability, and efficiency of the entire wind farm operation and the connected network. This philosophy encompasses multiple layers of protection and strategies to mitigate risks associated with electrical faults, environmental conditions, and operational failures. Implementing a robust system-level protection philosophy involves a combination of technical, operational and safety measures to ensure the efficient and safe operation of an offshore wind farm.
Design and Layout Considerations
Redundancy and Reliability
The electrical infrastructure should be designed with redundancy to ensure that failure in one part does not lead to a complete shutdown. This includes multiple pathways for power flow and redundant communication systems.
Zoning and Segmentation
Dividing the wind farm into manageable zones or segments to localise faults and prevent cascading failures as shown below:
Electrical Protection System
Overcurrent and Earth Fault Protection
The overcurrent and earth fault protection relays (ANSI 50/51) will be implemented to safeguard against excessive currents due to short circuits or overloads. These relays will be coordinated to the downstream as well as the upstream network to isolate the faulty section only. Appropriate coordination time intervals must be used to include fault detection, relay inherent and circuit breaker operating time delays as well as coordination and safety margins.
Differential Protection
Differential protection will be utilised for key components such as transformers, cables, reactors and filters to detect and isolate internal faults quickly. The main concept of differential protection is based on Kirchhoff’s current law and is shown below.
Distance Protection
Distance protection relays will be implemented to protect WTG array cables to detect and clear faults based on the distance from the relay location. This distance protection is illustrated below.
Overcurrent Earth Fault Protection
Instantaneous over current protection and timed over current (ANSI 50/51) provides fast tripping for high-magnitude faults and overload protection respectively. They provide simple and reliable backup protection.
Negative sequence over current element can also be applied for additional protection and to satisfy specialised device coordination requirements.
Monitoring features such as cold load pick and disturbance recorder will also be enabled to cope with inrush current which may cause maloperation/mis-judgment during energisation time.
Protection Philosophy for Offshore Wind Farms at Blake Clough Consulting
At Blake Clough we carry out protection coordination studies for onshore projects (PV, BESS, wind etc) and offshore wind farms. We can also provide the initial protection philosophy which is the starting point for protection design, as well as detailed protection settings.
