Internal lines and pooling substations on wind farms

A wind turbine generates electricity at the top of its tower, but that energy needs to reach the grid — often many kilometres away. The internal electrical system of a wind farm collects power from each turbine, raises it to transmission voltage, and delivers it to the grid connection point. This system is easy to overlook, but it affects cost, energy losses, reliability and especially land.

The path from turbine to grid

1. Turbine generator produces electricity at a relatively low voltage.
2. Turbine transformer steps up the voltage to the collection system level.
3. Collection system — underground cables or overhead lines — links groups of turbines.
4. Pooling substation collects the output of all turbines and steps up the voltage further.
5. Evacuation line carries the power from the pooling substation to the grid substation.
6. Metering at the interconnection point measures energy for billing and settlement.

The collection system

Underground cables

Cables are laid in trenches along roads or across land.

• Advantages: less visual impact, fewer land restrictions above ground, less exposure to weather and theft of conductor
• Considerations: higher cost, longer repair times when faults occur, careful installation and jointing needed, and trench routes cross many parcels

Overhead lines

Lines carried on poles or towers.

• Advantages: lower capital cost, easier fault finding and repair
• Considerations: visual impact, corridor restrictions beneath the line, exposure to weather and lightning, and theft risk for conductors in some areas

Many wind farms use a mix — cables near turbines and roads, overhead lines for longer distances.

Circuit design

Turbines are grouped into circuits (feeders). Design trade-offs:

• More turbines per circuit means less cable but more output lost if that circuit fails
• Ring or loop configurations add redundancy but cost more
• Cable sizing balances cost against electrical losses

The pooling substation

The pooling substation is the heart of the wind farm's electrical system. It typically includes:

• Incoming feeders from the collection circuits
• Switchgear and protection equipment
• Power transformers to step up to transmission voltage
• Reactive power compensation equipment where required
• Control, protection and communication systems
• Metering equipment

Substations need a dedicated, secure plot of land with good access and drainage. See solar power evacuation for similar issues on solar projects.

Shared pooling

In regions with many wind farms, several projects often share a pooling substation and evacuation line. Benefits include lower cost per project and less land use. But sharing needs clear agreements on ownership, operation and maintenance responsibilities, cost sharing and how capacity is allocated, and what happens if one party defaults or wants to expand.

Grid requirements

The connection must meet the requirements of the applicable grid code and connection agreement — covering voltage and frequency behaviour, reactive power, fault ride-through, protection coordination and communication with the system operator. Requirements are set by the relevant authorities and change over time; confirm current requirements during connectivity applications. See grid connectivity basics.

Losses

Electricity is lost as heat in cables, lines and transformers. Electrical losses are typically included in energy yield estimates. They can be reduced by appropriate cable sizing, shorter routes and efficient transformers — but each improvement has a cost.

Land and rights of way

The internal electrical system often crosses far more landholdings than the turbines themselves:

• Cable trenches across fields and along roads
• Overhead line poles and towers, with corridors beneath
• Substation plot
• Evacuation line route, potentially very long

Each crossing needs an agreement or right of way. Disputes or holdouts along a cable or line route can delay energisation of an otherwise completed wind farm. See wind project right of way.

Metering

Energy is measured at the interconnection point for billing and settlement. Metering arrangements — main and check meters, accuracy, testing and sealing — are governed by applicable regulations and agreements. Accurate, well-maintained meters avoid disputes. For industrial buyers using open access, metering also affects how energy is accounted for. See landed cost of open access power.

Maintenance

• Substation equipment inspection and testing
• Thermal imaging of connections
• Line patrols and vegetation clearance under overhead lines
• Cable fault location and repair

A fault at the pooling substation or evacuation line can take the entire wind farm offline, so substation reliability deserves particular attention.

In repowering

When a wind farm is repowered with larger turbines, the collection system and substation may need upgrading — higher capacity cables, larger transformers or new equipment to meet current grid requirements. See wind repowering in Tamil Nadu.

Common mistakes

• Planning cable routes without checking land ownership along them
• Designing collection circuits without considering redundancy
• Underestimating the land and approvals needed for the evacuation line
• Unclear agreements for shared pooling substations
• Neglecting substation maintenance because turbines get more attention

Where we fit

Through wind project development and wind site and land, we help secure land and rights of way for cable routes, substations and evacuation lines, and coordinate the electrical EPC partners who design and build them.