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Wind power from Nordex using EMKA

The Nordex Group has over 35 years of experience in the onshore wind turbine ­business, and it sets a benchmark for renewable energies. Since its foundation, the global technology company has installed wind turbines having more than 41 gigawatts of rated power. In 2019, Nordex decided to interact with another global player, EMKA. The turbines feature a unique compression latch from the world market leader based in Velbert, Germany. This latch secures vital access points and must withstand forces of up to 331 Newtons (N).

Small locking system – enormous responsibility

The importance of renewable resources for the global energy supply has been very much on the increase in recent years. This is because the dependence on limited gas or oil reserves has become too great. In Germany, the fossil fuel coal has already been replaced by wind power which has become the most important energy source in 2020. The Nordex Group has also contributed to this development. The technology company, based in Hamburg, Germany, is involved in the development, production, project development and maintenance of onshore wind turbines. Since the merger with ACCIONA Windpower in 2016, the Nordex Group has become one of the world’s largest manufacturers of wind turbines. The European public limited company employs 9,000 people in over 30 countries.

Special floor plates prevent serious accidents

Besides the ongoing development of its in-house product range, Nordex attaches great importance to the professional maintenance of its technologically complex systems. Therefore, the company continuously optimises individual components inside the turbine. In addition to the generator and the rotor, this also includes a unique compression latch, which is used in the hub, the rotor head of the turbine. These systems are sealed with special floor plates to ensure that the technician can work safely and not accidentally step into one of the hollow rotor blades. To gain access to the inner workings of the blades, the plates each have one or two inspection hatches. Four compression latches ensure these 15-kilogram hatches are securely installed in the floor plate. In the past, ensuring a sufficient inventory of these locking systems was not always possible, since the required quantity was not always available. Also, the housing was made of zinc die-cast, and the latch plate was made of unalloyed steel. This solution was susceptible to corrosion and caused a decrease in strength over time. The component also indirectly added high service costs. The reason: when checking the installed systems, it was not clear at first glance whether or not the component was in a locked position. Therefore, it could happen that a technician failed to close the hatches properly after maintenance. As a result, these hatches could become unhinged when the wind turbine rotated again. Therefore, the wind turbine had to be shut down again for some time in order to rectify the fault; the consequence: unforeseen additional costs over a longer period of time.

Since availability was a major concern, the responsible engineers at Nordex and the supplier of the floor plates decided in 2019 to replace the existing locking system inventory with a new lock. These unique designs were to identify the system‘s open/locked position clearly. In addition, the new solution had to withstand high pressure and resist impurities, dust, and lubricants. Because of these features alone, the locking systems would significantly increase the process reliability of the wind turbines. While the supplier acted as an intermediary, EMKA Beschlagteile GmbH & Co. KG received the call. “EMKA stood out because of its good performance in the past, its large product range and, at the same time, its great disposition to approach the customer,” says Peter Baars, development engineer in the rotor blade development department at the Nordex Group and responsible for the project. Following the approval, EMKA began developing a locking system that would meet Nordex’s specifications.

Tremendous forces also have an effect on the locking system

To ensure that the floor hatches are securely mounted in the cut-outs, EMKA developed a new compression latch made of stainless steel. This solution ensures that the cam not only closes the hatch but also firmly and vibration-proof due to the compression function. The lock can only be opened by turning it 180° with a squeare 8 mm key with marking. When rotating the square 90°, the cam moves 6 mm in the axial direction, releasing the compression. When rotating another 90°, the released cam rotates as well, and the hatch can now be lifted out. The actuation covers only half of the housing‘s head. Thus, each position of the locking system shows either OPEN (red) or CLOSED (green). This visual aid allows the technician to see whether the locking system is closed or open at a glance. The red/green markings are also smudge-tested according to DIN EN 62208 chap. 9.3 and DIN EN 61439-1 chap. 10.2.7.

Compliant with the European standard DIN EN 61373

Furthermore, EMKA had to consider the prevailing conditions in a wind turbine when developing the locking system. These conditions include, above all, the centrifugal forces, which have an increased effect on the turbine’s rotating hub. In the first step, therefore, the durability of dynamic loads of the latch cam combination had to be more than doubled – from the previous limit of 140 N to 337 N. In order to prevent unintentional opening during operation, the locking system’s design is vibration-resistant and shock-proof compliant with the European standard DIN EN 61373. In addition, the entire system is maintenance-free. This means there are no conflicting schedules regarding the systems‘ maintenance cycles

Over 850 plants equipped with EMKA closures

Nordex is significantly using its wind turbines to contribute to switching from fossil fuels to renewable energy sources. The design of this compression latch and its OPEN/CLOSED indicator enables EMKA to assist the technology company on this course. For 2022, Nordex has ordered many thousand locking systems to be installed in over 850 wind turbines. The wind turbine manufacturer also intends to rely on locking systems made in Velbert, Germany, in the future. The success of the recent developments led EMKA to include the design permanently in its catalogue portfolio.