Quick and Secure Fastening

The WPC system developed by STAUFF is a product range specifically designed for fixing electrical cables in wind turbine towers. Key features of the WPC clamps include simple, fast and tool-free assembly, permanent fastening of cables under adverse conditions and compliance with all industry-relevant requirements, among others governing electrical safety.

How much time does a well-trained team need to install electrical cables with cross-sections of 22 to 38 mm in a wind turbine tower some 100 or 150 metres tall? The answer to this question has implications for the competitiveness of the wind turbine manufacturer. And another question: How can you fix these cables in such a way that they are retained securely in position over many years under adverse conditions, at the same time providing the flexibility needed for the movement of the tower in strong winds? Once again, this is a crucial parameter for the lifetime of the cables and the availability of the wind turbine.

From the perspective of wind turbine manufacturers and operators, STAUFF provided the first satisfactory answer to these questions some years ago with a first generation of fastening system, developed from scratch specifically for use with electrical cables in wind turbines.

This fastening solution was based on the proven STAUFF clamp use for fastening pipes,tubes and hose in hydraulic systems. For Wind Tower Application, cables – either single cables or in rows – are laid into the recesses of a base plate, which is screwed or welded to the substructure, and fixed in place with screw covers. This solution has been used successfully, but the engineers at STAUFF continued to look for a solution that specifically simplifies assembly, without impairing the permanently fixed seating of the cables. To satisfy these requirements, a new range, designated WPC, was developed in collaboration with a leading wind turbine manufacturer.

Fast and tool-free assembly reduces installation costs

The basic concept of the WPC clamp: The cable holder is screwed onto a rail or similar – with various assembly options available – and the cable is inserted. A quick-clamping system, i.e. a handle, is used to close the counterside, which is hinged to the cable holder – and that's all there is to it Using the WPC clamp, technicians or installers can fasten cables without the need for tools. This is a key factor that simplifies installation in both the horizontal tower segment and in the erected tower, saving the manufacturer installation costs.

There are two basic versions of the new system available – the WPC for a single cable, and the WPC-Trefoil for three cables, fastened in a compact, clover leaf pattern. The system can accommodate cables with cross-sections of 22 to 38 mm.

Permanent tight cable seating

The fact that cables are permanently and tightly fixed in place is a key feature of the fastening system. The flexible elastomer cable holder provides consistent retention forces – even in the event of unexpected deviations in the tolerance of the outer cable diameter. An adjusting screw with locking nut is used to change the clamping pressure on the cable diameter. Once installed however, a certain tolerance needs to be allowed for, as the tower moves in the wind and the cable fastening system  must accommodate this movement.

A spring package in the quick-clamping system guarantees continuous pre-tension of the closure. A securing lock prevents unintentional opening of the clamping and closure mechanism. Tool-free assembly aids initial installation of the cables in the tower and maintenance or replacement of cables when the wind turbine is in operation.

Adapted for adverse conditions

Severe ambient conditions for electrical components are common in wind turbine towers: extreme temperatures and a corrosive atmosphere are to be expected. The metal components of the WPC range are available in various high-grade materials (steel zinc/nickel-coated for onshore wind turbines, V4A stainless steel for offshore wind turbines).

The steel version with a highly effective corrosion protection coating based on a zinc nickel finish, has proven to be a cost-effective alternative to stainless steel in many different applications.  It achieves a service life of some 1,200 hours in the salt spray test, which is higher than the applicable standards required in the automotive industry, among others.

The elastomer used in the wind power clamps is temperature-stable between – 45°C and +90^°C (in continuous use; temporary use up to +125°C). It also absorbs no water in the presence of moisture and so remains dimensionally stable.

Fully tested: Fire protection, short circuit resistance, mechanical stress

STAUFF WPC clamps meet all relevant fire protection requirements and have also been tested and approved as fire protection material SA-V0 according to UL 94. STAUFF has also tested the electrical properties – particularly the short circuit resistance of the WPC range – in conjunction with a wind turbine and a cable manufacturer. This demonstrated the unrestricted suitability of the fastening system for the transmission of high currents.

Mechanical stress tests confirm a high axial retention force with very good protection of the cable jacket. Further tests showed that low temperatures do not have a negative impact on the retention forces in the fastening system. On the contrary, the retention force was even higher than in the test conducted at room temperature. This is where the elastomer / metal material combination in particular has a positive effect.

Broad-based range – customised products also available

These properties make the WPC system ideal for the fastening of electrical cables on onshore and offshore wind turbines. Various basic versions for a single cable and for three cables are available ex-stock. And the modular design of the system enables it to be adapted to individual applications. For instance, one or two clamp bodies with replaceable elastomer could be used as cable protection for different cable diameters.