Lightweight and robust – PFISTERER optimises 66 kV connection technology for offshore applications

The SEANEX inner cone solution by PFISTERER is an offshore variant of the successful CONNEX HV connection system that is specially adapted for 66 kV inter-array cabling. The new offshore accessories combines all the proven performance features – salt water resistance, solid insulation, pluggable and touch-safe – yet it is much more compact, lighter in weight, and lower in cost.

Moreover, the mechanically robust inner cone technology offers clear advantages in terms of installation, corrosion resistance and reliability in harsh environments.

The optimised SEANEX HV connector together with the corresponding cast resin joint forms a perfect fitting for connecting and cabling 66 kV offshore wind farms. PFISTERER adapted the system specifically for this application. With CONNEX, the company is the only manufacturer with an offshore-certified solution that has been tried and tested for 20 years. PFISTERER is involved from the outset in developing numerous platform projects for offshore grid connections. "Because of the growing number of projects, and particularly with the changeover from 33 to 66 kV in the wind farm networks, we set ourselves the goal of optimising our existing solution for even easier and more flexible wind turbine installation. The inner cone technology is optimally suited for this application and guarantees reliability and durability well beyond the projected operational life of a wind farm. In combination with the cast resin joint, the solution is unique," explains Dr. Peter Müller, Head of Renewables at PFISTERER. During the development process, HV specialists at PFISTERER always kept the design-to-cost principle in mind. Accordingly, the HV fittings have been strictly optimised for offshore requirements. Thanks to a significantly more compact design, the new cast resin joint measures just 39 cm long and weighs 28 kg. "Aside from the lower costs, these advantages give our customers greater flexibility for handling and installing the HV fittings," Müller points out.

Fast installation and long-term reliability at sea

The dry, SF6 gas-free cast resin joints with voltage tap and SEANEX connector by PFISTERER are solid-insulated, resistant to salt water and UV radiation, and submersible. They are suitable for various cable types up to a diameter of 800 mm². In addition, an integrated longitudinal water barrier in the joints prevents water that is entering because of a cable fault from getting into the other cables. During wind turbine installation, the pluggable connection between the sea and tower cable allows individual construction phases to be clearly separated from each other. This simplifies planning and cooperation between the different project partners. Furthermore, the possibility for onshore preinstallation of the joints in the tower segment or transition piece (base) results in shorter offshore installation times. The compact and more lightweight design of the fitting also allows more flexible positioning. Then all that remains to be done at sea is to connect the joint and SEANEX connector. The connectors have a rotatable bell flange that always fits into the corresponding socket, even with preassembled cables. This means the cable is never twisted.

Advantages of the inner cone system in HV applications

In 66 kV applications, the inner cone technology offers numerous advantages over outer cone connections. Maintenance-free inner cone fittings are touch-safe even in the event of a fault, and have far greater stability owing to their separate mechanical and electrical contacts. As a result, they cope better with sudden load changes. It is not necessary to build a transition box. "There is really no limit to the continued development of the inner cone," says Alejandro Escobin, Senior Product Manager CONNEX. "Today's new wind turbines have an output two to three times higher than those of 20 years ago - and we are still nowhere near the end in terms of performance improvements."

As the inventor of the inner cone system, PFISTERER has decades of experience in connecting offshore installations. With CONNEX, the manufacturer offers a complete product range for all voltage levels from 12 to 550 kV. As a result, all connections in wind turbines can be implemented using a uniform technology - from the switchgear and transformers to connecting the sea cable. PFISTERER is currently providing equipment for connecting 102 Siemens turbines in the new East Anglia One (EA1) wind farm. With a total output of 714 MW, this is the first large-scale wind farm at the 66 kV voltage level.