Wind power
Enclosure and housing solutions for offshore windmills
The use of wind power offshore is one of the future technologies. At the moment offshore wind farms with an overall power of 45 GW are being planned around the globe. However, the Horns Rev project shows that the sea site can also raise problems. Solutions are needed that protect sensitive electronics against extreme weather and increasing heat loss.
Energy supplies that offer an alternative to the slowly declining classic energy supply's of oil, coal and natural gas are more in demand than ever today. Wind power energy is an alternative that now has a two-digit growth rate.
The number of windmills on-shore and above all offshore is continuously increasing. However, reliable operation under extreme atmospheric conditions requires high quality components and systems.
The technology core of windmills is in the nacelle on which the wind wheel is suspended. Components like gearbox, parking brake, generator, heat exchanger, hydraulic power unit and switchgear cabinet are located here. At a height of over 100 m the nacelle is extremely susceptible to a lightning stroke and also exposed to mechanical stresses and vibration. In addition large temperature variations and extreme weather conditions have to be handled by the windmills. Corrosion and condensation are big enemies for the electronics. The narrow space of the nacelle is equipped with devices and enclosures with high packing density. With the increasing power of the units the heat loss within the nacelle also increases. Thus the question of climate control arises in order to avoid downtime of the system due to the electronics overheating.
High demands are made on individual components. Enclosures and housings are made from stainless steel due to corrosion hazard by the salty sea air. Moreover mechanical stresses and vibration require a reinforced and vibration damped design of the enclosures. The increasing capacity of the electronics also demands an EMC protection of the "packaging" in order to keep the disturbances at a very low level. This is also the case for fans and cooling units. At the bottom of the wind power tower special outdoors enclosure systems as well as container solutions are required that accommodate parts of the current/energy distribution and control. For these requirements Rittal as a system supplier for enclosure and housing technology provides suitable solutions.
For safe accommodation of electronics in the nacelle directly behind the rotor, space saving and solutions with high protection category that can be integrated without problem, enclosures like the Rittal compact AE range are required. The AE range with a maximum protection category of IP 66 comprises more than 200 solutions.
Rittal offers the Top Enclosure System TS 8 as control enclosure solution for the mains connection to the suppliers. The TS 8 system is also available in sheet steel or stainless steel and can be bayed and is easily accessible from all sides thanks to its modular and flexible design. The enclosures save time and costs in assembly, maintenance and repair and minimises standstill times.
With regard to vibration damping and mechanical stress it is possible to reinforce small enclosures, operating panels and large enclosures and fit vibration damping components. If required, oscillation and vibration tests are carried out at Rittal. In addition to reliable packaging solutions the efficient climate control of electronics ensures smooth operation of windmills. This is a serious topic with regard to increasing heat losses within the nacelle due to more and more powerful electronics of modern systems. As a solution Rittal offers climate control units with hermetic separation of interior and exterior air circuit so that the air in the electronic enclosure cannot be mixed with the salty sea air. Protection category IP 55, either spray-finished sheet steel or stainless steel enclosure as well as EMC protection mean these cooling units are ideal for use in rough environment.
Learned from Horns Rev
When handling the offshore project "Horns Rev" 15 km off the Danish west coast at Esbjerc, a charge-specific fault was found in the transformers in autumn 2003. The insulation was insufficient. At a later point in time problems also occurred in a generator. A thorough analysis showed that the problem was due to a manufacturing error. A series of 70 generators in total, 55 in Horns Rev had deficiencies. After localisation of the remaining 15 generators, the manufacturer of the windmills - the Danish Vestas - decided to exchange all 70 generators. The most cost effective solution was to dismantle all nacelles and bring them back to the coast. This offered Vestas the possibility to analyse, under controlled conditions, what had the biggest impact two-year use in rough offshore environment. Vestas got basic knowledge: For the next off-shore wind farms, North Hoyle and Scoby Sands in Great Britain, with 30 windmills of the V80-2,0 MW type each, the experience has already been realised. "Scoby Sands has been put into operation and North Hoyle works to complete satisfaction" emphasises Vestas. For this reason no major problems are expected in these wind farms and for the next generation of the windmills of type V80-2,0 MW.