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Close up - Alstom Haliade 6MW prototype

FRANCE: In June, Alstom installed the first prototype of its Haliade 6MW offshore wind turbine at a test site in northern France. Windpower Monthly technology writer went along for a look.

Alstom's distinctive Haliade 6MW turbine (pic Eize de Vries)
Alstom's distinctive Haliade 6MW turbine (pic Eize de Vries)

Click here to view larger image of Alstom Halidade 6MW turbine

This month Alstom’s 6MW Haliade 150 prototype produced its first kWh’s as part of a comprehensive certification programme at an onshore site near Nantes. A second prototype, currently being manufactured in the Atlantic port city Saint-Nazaire, is destined for a test position at the ‘Belwind’ wind farm off the Belgian coast.

The current prototype holds a temporary record for being the world’s first turbine with a rotor diameter in excess of 150 metres (150.8m). From a distance, the turbine is easily recognisable with its unusual nacelle shape with characteristic ring generator and integrated helicopter-hoisting platform. On closer inspection, one can also make out a rather simple looking spoiler attachment is on the round inner blade section. This aims to enhance aerodynamic lift performance without substantially increasing resistance or drag.

Offshore simulation

Being installed close to the river Loire, all Haliade main components including the three 73.5-metre long blades were transported by water. Pointing at the confined area between river landing area and turbine, Alstom’s VP Wind Offshore Frédéric Hendrick said the arrangement aimed to simulate space-limited jack-up deck manoeuvring conditions.
The Haliade nacelle (pic Eize de Vries)

(click on image for full size pic)

The mini-jacket was designed so its dynamic behaviour is similar to a ‘real-size’ offshore jacket. The design itself incorporates a spacious upper platform with two-tonne service crane. What is impressive are the massive structural corner elements forming an interface between the lattice corner sections and central tubular steel section, to which both the E-module and tower are mounted on. The three-storey E-module houses the power electronic converter, switchgear and medium-voltage transformer (bottom).

Hendrick explained that Alstom decided to locate Haliade’s electronics at the bottom of the tower in order to minimise top head mass (nacelle + rotor). Another key consideration for ‘down tower’ power electronics placement was reduced downtime by enabling easier and faster service access. Often-quoted added benefits include reduced vibration-related component failure risk and superior protection against fluctuations in operating temperatures and humidity.

Efficient transportation

Alternatively all power electronics including converter and medium voltage transformer are located inside the nacelle. This ‘up tower’ solution enables pre-testing and pre-commissioning of the nacelle prior to installation, potentially enabling faster and simpler installation. Transporting medium-voltage compared to low-voltage solutions always reduces power losses and allows the use of lighter less expensive copper cables.

The Saint-Nazaire facility for Haliade nacelle assembly is temporary, because a major industrial plan foresees in building four new Alstom factories. The nacelle assembly and generator manufacturing plants in Saint-Nazaire will become operational in 2014, while blade manufacturing and tower (internal) assembly plants in Cherbourg further north in France are planned for ramp-up in 2015. They will provide 1000 direct jobs and another 4000 indirect jobs.

During our visit to the facility the second nacelle rear section mounted on a rail-type heavy-duty carrier was awaiting the arrival of the water-cooled ring generator measuring around 2-metres in length and a 7.6-metre outer diameter. Electrically the Converteam (now GE) medium-voltage generator consists of three 120-degree stator sections, and each section feeds power into a separate power electronic converter for enhanced system redundancy.

'Pure Torque'

Unfortunately full details of Alstom’s 'pure torque' principle as applied in the Haliade could only be viewed on an engineering drawing inside the hall. The principle is based upon a rotor hub assembly incorporating two main bearings, which rotates around a hollow stationary main pin and directly transfers rotor-bending moments into the main chassis and tower. The hollow pin also offers service access to the hub. The hub further has a flexible linkage to the generator rotor part, which rotates on a separate third bearing. By fully separating rotor-induced bending moments and rotor torque, only ‘pure torque’ is being transmitted to the generator rotor.

Finally, Alstom from the onset has introduced an industrial nacelle assembly process based upon principles known as Toyota Production System, incorporating concepts like ‘avoid waste’ (lean) and continuous improvement processes. "From 2014 onwards nominally 100 turbines can be built annually in a line process involving multiple tag stations, but this will not be a maximum number. Building one turbine will take 25 days subdivided into ten distinct 2.5-day tag-time stages of 2.5 days each," Hendrick said.



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