ExxonMobil for Wikov
in the Sea of Orcs

15. 11. 2017

The Saudi Arabia of tidal power

by Lukas Steiner, Wikov Industry

The Pentland Firth, An Caol Arcach in the Scottish Gaelic, meaning the Orcadian Strait, is a strait which separates the Orkney Islands from Caithness in the north of Scotland. Prior to the Norse occupation of Orkney the strait was known as the "Sea of Orcs" – a reference to the Pictish tribe who inhabited Orkney. The Firth is well known for the strength of its tides, which are among the fastest in the world. Currents of up to 5 metres per second make the Pentland Firth potentially one of the best sites in the world for tidal power*.

The MeyGen project in Pentland Firth has become the world’s largest tidal-stream project to date
In 2008 tidal power developer Atlantis Resources Corporation (ARC) announced it was considering a site near the Castle of Mey for a computer data centre that would be powered by a tidal scheme in the Firth. In October 2010 MeyGen, a consortium of ARC, Morgan Stanley and International Power, received operational lease from the Crown Estate to a 400 MW project for 25 years. Consent was granted in September 2013 for MeyGen to build a 6 MW demonstration project of 4 turbines in the Phase 1A . The second phase would install up to 270 turbines generating 398 MW.

Andritz Hydro Hammerfest, based in Glasgow (UK) and part of Andritz Hydro in Austria, is supplying three of the four turbines for the initial phase. The project is considered to have the utmost significance for power generation and potentially for the future of sustainable energy supply. The three turbines are fitted with a Wikov planetary gearbox using flexible pin technology which along with a flexible approach won the contract for Wikov to deliver gearboxes to Andritz Hydro. The first on-site construction stage involves the installation of four 1.5 MW turbines and the very first turbine started producing power already on November 15, 2016.

The Wikov’s patented “flexible pin” with an overload stop is a unique load-sharing feature created and used for the past three decades by Orbital2. Majority of epicyclic gearboxes have a fixed pin arrangement as standard, with a maximum of three or four planets on one carrier, which limits torque capacity. In contrast, Wikov’s gearboxes – applying flexible pins and a differential split torque arrangement of epicyclic gear trains – offer both, increased torque capacity and reduced size and weight.

Flexible pin in a SeaGen tidal turbine
The flexible pin concept has already proved its worth many times over. It was chosen for the 1.3 MW tidal turbine built in 2008 by SeaGen in Northern Ireland’s Strangford Lough, the world’s first commercial tidal-stream power station. Since then, Wikov has sold an additional gigawatt’s worth of wind turbine gearboxes equipped with flexible pin technology.

But with the MeyGen project, Wikov’s technology is about to face its biggest test. The requested lifetime for these gearboxes is 25 years, and they’ll be serviced only once every five years. The rest of the time they should stay on the bottom of the sea. The nacelle is filled with nitrogen, so you won’t be able to send a frogman down to take a look if something goes wrong, The gearbox must perform reliably from the very beginning to the end of the requested lifetime. That reliability depends in large part on the bearings and the quality of lubricant. The latter mentioned is mostly ignored however it is extremely important for the lifetime of the gearbox internals. Therefore in this respect Wikov partnered with ExxonMobil, which had recently launched a new synthetic lubricant – Mobil SHC Gear 320 WT – specifically formulated for renewable and wind-energy applications. After running in-house tests on a 3-MW planetary wind gear, the lubricant displayed the right properties, including high-viscosity stability, strong anti-foam properties, and better fluidity at cold temperatures. It is especially formulated to resist micropitting of modern, case hardened gearing and can operate in both high and low temperature environments.

Mobil SHC Gear 320 WT
Mobil SHC Gear 320 WT has been formally approved for our flexible-pin technology in wind applications. Following the outstanding performance of the oil in wind turbines, we tested it for tidal power applications, and found it to be an ideal lubricant for this application as well. It features a higher viscosity index, easier and faster startup in cold environments due to lower viscosity and thus limited need of oil pre-heating, and higher protection against wear at high temperatures – an important feature when you consider that temperatures can rise to 100ºC in the load area. As for tidal power, our gearboxes have a long track record of success in some of Europe’s largest projects and after evaluations Wikov decided for the Mobil SHCTM Gear 320 WT synthetic oil which is the most suitable lubricant for the flexible pin in harsh conditions of wind and more significantly tidal applications, says Jan Vosátka, technical director at Wikov Industry.

* Tidal energy is classified as an ocean technology that converts the energy caused by cyclical movements of the sea into electricity. There are three ways to generate electric energy from the tides; one of these is via underwater propellers (similar to windmills) powered by tidal streams.