This compression latch is used in the hub, on 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, supply issues have been problematic, plus the generic housing used was made of die-cast zinc, and the latch plate was made of unalloyed steel. This material combination was susceptible to corrosion and caused a decrease in strength over time.
The component also indirectly added high service costs because when checking the installed systems, it was not clear at first glance whether or not the component was in a locked position. The concern was that a technician might just possibly fail to close the hatches properly after maintenance. As a result, these hatches could become unhinged when the wind turbine rotated again. This meant that the wind turbine had to be shut down again in order to rectify the fault, so incurring additional costs over the service life of the installation.
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.
Peter Baars, development engineer in the rotor blade development department at the Nordex Group and responsible for the project, says: “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.”
To ensure that the floor hatches are securely mounted in the cut-outs, Emka developed a new compression latch made of stainless steel to resist the forces and corrosive environment involved. This solution ensures that the cam not only closes the hatch firmly but is also vibration-proof due to its compression function. The lock can only be opened by turning it 180° with a square 8 mm key with open/closed 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 so that 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.
In addition, Emka had to consider the prevailing conditions in a wind turbine when developing the locking system, these 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. Plus, the entire lock system is maintenance-free, so there are no conflicting schedules regarding the system’s maintenance cycles.