Unassailable Fit & Forget Pressure Moulded Cable Systems for Hostile Environments

Unassailable Fit & Forget Pressure Moulded Cable Systems for Hostile Environments

SMI Supports Meygen Migration to Wet-Mate Connectivity


Countries across the world are turning to offshore wind and tidal sources to generate low carbon electricity. The marine environment in which equipment is installed is extremely hostile. To ensure continued generating performance and minimise servicing costs, engineering and supporting infrastructure must have a strong marine pedigree.

Wave and tidal energy generation promise predictability in output that wind power will never be able to offer. However, wave and tidal platforms have to operate in extremely hostile offshore conditions, with subsea cables exposed to significant forces and being hard to access for repairs and maintenance. Operators are increasingly aware of the economic benefits of reliable, high performance cable systems.

Scientific Management International’s (SMI) cable systems are designed to withstand the corrosive seawater and high currents of the marine environment; to be easy to install and maintain, minimising downtime and maximizing uptime for customers.

SMI designs and manufactures connector and cabling solutions that form the central nervous system of offshore power generation equipment. Our technology delivers export power, system control and monitoring data, regardless of the state of the marine conditions in which they are operating. The ‘fit and forget’ approach ensures the long-term performance of our solutions, often to the full life of the platform. This avoids complex servicing and replacement programme, reducing marine logistics time and offering considerable through-life economies.

Figure 1 Penetrating glands for tidal energy system

Cable systems, wet and deck mate connectors & glands

SMI’s harnesses are application specific and can incorporate penetrating glands, deck-mate or wet-mate connectors. Meygen are amongst the operators who are favouring wet mate connectivity to reduce the need for marine vessel support and de-risk installation processes.

Stab plates are design to integrate the connectors,  joined as part of turbine installation.

SMI have been the technical and commercial partners of GISMA, the industry leading subsea connector manufacturer, for nearly three decades. GISMA’s oil-filled and pressure balanced Series 80 connectors support high voltage applications and are also available with power and fibre optic contacts for communication and control functions.

smi wet mate three phase harness
Figure 2 SMI wet mate three phase harness

Developed in collaboration with University of Applied Science in Kiel the contacts have been designed with the ideal contour to keep partial discharge very low and prevent damage to the insulating materials in concentrated electrical fields. The fluorelastomer, selected thermoplastic materials and the oil have been selected for their dielectric strength.

SMI’s thermoplastic moulding technology not only seals the connector or gland but also enables the presentation of multiple cables to the rear of one connector.

Figure 3 GISMA Series 80 receptacle for stab plate

Material Selection for Cables Harnesses

The material used for the cable jacket depends on the specific application and the required properties.

Polyethylene (PE)

PE is a thermoplastic material that is inert in the ocean and does not degrade over time. It has excellent dielectric characteristics and low moisture permeation. However, PE is difficult to process and bond to other materials. The material used for the cable jacket

Thermoplastic Polyurethane (TPPU)

TPPU is another thermoplastic material that is flexible, wear-resistant, and mechanically tough. It also has excellent ageing resistance against environmental humidity, ozone, UV radiation, and microbes. However, TPPU absorbs moisture and its dielectric strength is lower than PE.

Thermoset Polyurethane (TSPU)

TSPU is a thermosetting material that is easy to mix and pour. However, it has a high water absorption rate and a lower dielectric strength than PE and TPPU. It also relies on mechanical adhesion, which makes it susceptible to delaminating. For applications where ease of processing and low cost are important, TSPU may be a good choice.

The Best Material for Cables Harnesses

For applications where long-term sealing performance is critical, PE is the best choice. For applications where flexibility and mechanical toughness are important, TPPU is a good option.  For Meygen, a polyethylene (PE) cable jacket was specified providing the best electric insulation.

Bonding and Amalgamation for Long-Term Sealing

One of the most important factors in ensuring long-term sealing is the bonding of the cable jacket to the termination moulding. This bonding can be either mechanical or chemical.

Mechanical bonding relies on roughening the adhering surfaces to increase surface area and interlocking. This can be achieved by abrading, grit blasting, or etching the surfaces. However, mechanical bonding is not as strong as chemical bonding.

Chemical bonding occurs when the atoms of adjacent materials containing free electrons and electron holes in the respective outer shells, are encouraged to transfer across, to achieve a lower state of equilibrium, resulting in a chemical bond. This can only happen when sufficient energy is introduced to excite the free electrons resulting in transfer to the adjacent electron holes in the other material. By definition, the bond will be stronger than the weaker of the two materials and orders of magnitude greater than any mechanical joint.

High pressure and temperature provided by the thermoplastic moulding process provides the energy required for this bonding to occur.

Figure 4PE amalgamation on 3 phase wet mate connector

Another important property of thermoplastics is they can be re-melted many times. This is what happens to the granules when heat is added to transition from solid to molten form, before it is injected under high pressure into a tool, to manufacture a termination. The cable jacket is also melted during this process and flows together with additional introduced polymer so that it cools into a completely homologous material. Effectively, the cable jacket shape is tailored to incorporate the profile required for the termination without the need for any join or interface. This amalgamation process is absolutely key to long-term sealing, as with no interface present, water can never enter a thermoplastic moulding at this critical junction.

A poorly designed or manufactured cable harness can lead to premature failure, costly downtime and lost revenue. Particularly concerning where access to the asset is governed by tides, weather windows and vessel availability.

Wet-mate connectors are of particular value to wave and tidal energy systems making them easier and safer to install and maintain.

Figure 5 SMI harness installed by Meygen

SMI’s commitment to quality and customer service has made it a trusted partner for leading offshore energy companies around the world. The company’s cable systems are currently in use on a wide variety of projects.

Scientific Management International Ltd

01264 357357    www.smi.group