An offshore substation is the electrical hub of a wind farm at sea. Each turbine produces power, but that power must be collected, controlled, and sent long distances to land. The substation sits on a steel platform above the ocean and connects many undersea array cables.
It matters because raising voltage at sea reduces energy losses and makes large offshore wind farms practical.
Key Facts
- Power is P = VI, so for the same power, higher voltage means lower current.
- Cable heating loss is P_loss = I^2R, which is why substations step up voltage before export.
- Array cables usually collect medium-voltage AC power from turbines, often around 33 kV to 66 kV.
- A transformer raises voltage by the turns ratio: V_s / V_p = N_s / N_p.
- Export cables carry power from the offshore substation to an onshore grid connection point.
- Switchgear, transformers, protection relays, and control systems help route power safely and disconnect faults.
Vocabulary
- Offshore substation
- A platform at sea that collects electricity from wind turbines, raises its voltage, and sends it to shore.
- Array cable
- An undersea power cable that connects individual wind turbines to the offshore substation.
- Export cable
- A high-voltage undersea cable that carries electricity from the offshore substation to land.
- Transformer
- An electrical device that changes AC voltage using coils and magnetic induction.
- Switchgear
- Equipment that controls, protects, and isolates electrical circuits in a power system.
Common Mistakes to Avoid
- Thinking the substation creates energy, which is wrong because the wind turbines convert wind energy into electrical energy and the substation only collects and conditions it.
- Forgetting that higher voltage lowers current for the same power, which is wrong because P = VI means current decreases when voltage increases at constant power.
- Treating array cables and export cables as the same, which is wrong because array cables gather power within the wind farm while export cables send combined power to shore.
- Ignoring cable resistance, which is wrong because long undersea cables lose energy as heat according to P_loss = I^2R.
Practice Questions
- 1 A group of turbines sends 120 MW to an offshore substation at 66 kV. What is the current, assuming three-phase details are ignored and P = VI?
- 2 A transformer steps voltage up from 66 kV to 220 kV. If the primary coil has 600 turns, how many turns should the secondary coil have?
- 3 Explain why an offshore wind farm uses a substation at sea instead of sending low-voltage power from every turbine directly to shore.