Tidal Stream Turbine

Overview

Tidal currents are slow but utterly predictable, the tides run to a timetable set by the moon, decades in advance, and seawater is about 800 times denser than air, so a modest current carries a lot of energy. A tidal stream turbine harvests that energy the way a wind turbine harvests wind, but underwater: a bladed rotor turns in the flowing tide, a drivetrain spins a generator, and a power-electronic converter conditions the output for the grid. Because the machine sits on the seabed in moving saltwater, the hard problems are sealing, corrosion, and surviving the loads when a spring tide runs at full strength.

How it works

Flow turns the Rotor Assembly, whose three blades are carried on a hub fitted with a Blade Pitch Mechanism. Each blade rotates in its own root bearing so the controller can set the angle of attack, trimming power in strong currents and feathering the blades edge-on to ride out storms. The rotor drives a main shaft inside the Nacelle, a pressure housing that runs the shaft on bearings behind oil seals to keep seawater out of the dry machinery space.

A slow rotor makes poor use of a compact generator, so the shaft first passes through the Speed-Increasing Gearbox, which steps the speed up before driving the Permanent-Magnet Generator, a permanent-magnet machine that produces variable-frequency AC as the rotor speed changes with the tide. That raw output is fixed by the Power Converter: a back-to-back IGBT stage that rectifies the generator current and re-inverts it to clean grid-frequency power, all sealed inside its own pressure vessel and cooled by the surrounding sea.

The whole machine is anchored by the Foundation & Yaw Mount, a ballasted gravity base with a yaw bearing that lets the nacelle face the dominant flow. Power leaves through the Subsea Export Cable, an armoured subsea cable that also carries telemetry fibres back to the Turbine Controller supervisor onshore.