Highest requirements for lightning strikes
The experts at Jäger are meeting these challenges, but the fundamentals for this must first be clarified. The hub of a wind turbine is bolted to the rotor of the generator from 72 to 108 double ends, depending on its size. Each of these metal bolts should be fully protected in the shaft area. This means that the hose must not only fit tightly, but also be precise in its length and diameter. The special compound selected must also meet the requirements permanently: It must be extremely flexible and must not be damaged at all during the assembly process. A tiny hole would destroy the surge protection. In addition, it must be ensured that no moisture can penetrate between the shaft of the double end and the hose.
Jäger tests such properties in a special plunge pool. The double ends, in this case with a diameter of 42 millimeters and a length of 506 millimeters, are already covered with the special hose. The pressure generated simulates the pressure prevailing on the system under full load. The double ends and the special hose are designed for the life cycle of a wind turbine, which is calculated at 25 years.
But the engineers have not yet reached that point. All previous attempts to apply a hose to the double ends have failed. All too often the hose, whose inner diameter is smaller than the outer diameter of the double end, is overstretched and no longer fulfills its intended function. The quality of the manufactured components is not in question. The assembly process is the key.