The capacity of an offshore wind farm is only one part of the grid integration challenge.
The strength of the network at the point of connection also shapes how the project will behave.
A weak grid connection is characterised by relatively low short-circuit capacity compared with the size of the generation being connected. Under these conditions, electrical changes within the wind farm can have a greater influence on the surrounding network.
This makes network strength an important design consideration from the beginning of the project.
Why offshore wind may connect to weaker networks
High-quality offshore wind resources are often located near remote coastal regions. These areas may have lower local electricity demand and less developed grid infrastructure than major industrial centres. Connecting a large wind farm can therefore represent a significant change to the local system.
The paper discusses this in the context of Japan, where offshore wind sites near areas such as Akita and northern Hokkaido may connect to parts of the network with lower strength.
Similar engineering challenges can arise in other markets. At Viking Wind Farm in Shetland, the local network was very weak. Turbine and transformer energisation therefore had the potential to create large voltage dips.
Why network strength changes the response
When a transformer is energised, it draws magnetising inrush current. On a strong network, the resulting voltage dip may be relatively limited. A weak network can experience a larger disturbance from the same event.
Cable energisation and reactive power switching can also have a greater effect. This may create difficulties with voltage fluctuation limits or influence the operation of connected equipment.
The project team therefore needs to assess more than normal operating conditions. Initial energisation, restoration sequences and unusual network configurations can all affect the result.
The implications for commissioning
A weak connection may require a carefully controlled energisation sequence. Rather than switching several transformers or cables together, assets can be energised in stages. This allows each transient to decay and gives the network voltage time to recover.
The number of transformers that can be energised together will depend on system strength. The paper notes that only a small number may be suitable for simultaneous energisation on a weak rural network. A stronger connection could permit more equipment to be switched during the same stage.
Where voltage dips remain excessive, controlled switching may be required.
Designing for the connection point
A weak connection should influence equipment selection and study requirements. Transformer inrush needs to be modelled against realistic network conditions. Long cable behaviour should be considered alongside any shunt compensation. Control systems may also need careful coordination.
The design must reflect the network the wind farm will actually connect to, including credible minimum fault level conditions. Using assumptions based on a stronger system could underestimate the likely voltage response.
Early studies create more options
Detailed studies allow the proposed connection to be tested before commissioning. RMS analysis can assess wider system performance. EMT simulation can then examine fast switching events and nonlinear transformer behaviour.
The results may support a revised energisation sequence, Point-on-Wave switching or changes to reactive compensation.
Early assessment gives the project team time to incorporate these measures into the design. Discovering the same issue during commissioning would leave fewer options and could delay the connection programme.
Weak grid conditions do not prevent offshore wind integration. They require the project to be developed with a clear understanding of the network from the outset.
Click here to download the full technical paper to explore weak grid connections, voltage disturbance and offshore wind integration in greater detail.
