Putting Alstom's Haliade 6MW to the test

First power generated last month, as certification gets underway

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

The prototype, with its 150.8m rotor diameter, features a distinctly-shaped nacelle with a characteristic ring generator and integrated helicopter-hoisting platform.

Looking upward, and on closer inspection, it is possible to make out that a 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 of the Haliade’s main components, including the three 73.5m-long blades, were transported by water. Pointing at the confined area between the river’s landing area and the turbine, Alstom’s vice-president for offshore wind, Frédéric Hendrick, said the arrangement aimed to simulate manoeuvring conditions on space-limited jack-up deck.

The mini-jacket was designed so that its dynamic behaviour would simulate a real-size offshore jacket. The design itself incorporates a spacious upper platform with two-tonne service crane. The massive structural corner elements, forming an interface between the lattice corner sections and central tubular steel section, are truly impressive.

The three-storey E-module houses the power electronic converter, switchgear and medium-voltage transformer. Hendrick explained that Alstom chose to locate Haliade’s electronics at the bottom of the tower to minimise top head mass (nacelle plus rotor). Another key consideration for placing the power electronics at the bottom of the tower was to reduce downtime by enabling easier and faster service access. Additional benefits can include reducing the risk of vibration-related component failure and superior protection against fluctuations in operating temperatures and humidity.

Efficient transport

An alternative location for all power electronics, including converter and medium-voltage transformer, is inside the nacelle. This ‘up tower’ solution enables pre-testing and pre-commissioning of the nacelle before it is installed, potentially resulting in faster and simpler installation.

Transporting medium-voltage compared with low-voltage solutions generally reduces power losses and allows the use of lighter and cheaper copper cables. The Saint-Nazaire facility for assembling the Haliade nacelle is temporary, because the company’s industrial plan foresees the construction of four new Alstom factories in the area.

A new nacelle assembly plant and a generator manufacturing facility in Saint-Nazaire will become operational in 2014, while blade manufacturing and tower (internal) assembly plants in Cherbourg are planned for 2015. Combined, these facilities should provide 1,000 direct jobs and 4,000 indirect jobs.

Pure Torque

It is unfortunate that full details of Alstom’s 'pure torque' principle, as applied in the Haliade, could only be viewed on an engineering drawing.

 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 carrier chassis and tower. The hollow pin offers service access to the hub. The hub is flexibly linked 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.

Alstom applies the principles of the Toyota Production System to its nacelle assembly process. This incorporates concepts such as ‘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," according to Hendrick.

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