The current model holds the record for being the world's first turbine with a rotor diameter in excess of 150 metres (150.8m). The turbine is easily recognisable with its unusual nacelle shape and characteristic ring generator and integrated helicopter-hoisting platform. On closer inspection, one can also make out a simple looking spoiler attachment on the round inner blade section. This aims to enhance aerodynamic lift without substantially increasing resistance or drag.
The mini-jacket was designed so its dynamic behaviour is similar to a real-size offshore jacket. The design incorporates a spacious upper platform with a two-tonne service crane. The massive structural corner elements forming an interface between the lattice corner sections and central tubular steel section are impressive. Both the E-module and tower are mounted to these. The three-storey E-module houses the power electronic converter, switchgear and medium-voltage transformer.
Alstom put the electronics at the bottom of the tower to minimise top head mass (nacelle + rotor). Another reason for down tower power electronics placement was to reduce downtime by enabling easier and faster service access. Other often-quoted benefits include reduced vibration-related component failure risk and superior protection against fluctuations in operating temperatures and humidity.
All power electronics including converter and medium voltage transformer are conversely located inside the nacelle. This enables pre-testing and pre-commissioning of the nacelle prior to installation, potentially enabling faster and simpler installation. Transporting medium-voltage rather than low-voltage solutions reduces power losses and allows the use of lighter less expensive copper cables.
When visiting the facility, I saw the second nacelle rear section mounted on a rail-type heavy-duty carrier 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, each feeding power into a separate power electronic converter for enhanced system redundancy.
Alstom's 'pure torque' 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, which 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 transmitted to the generator rotor.