Lowering the Cost of Connection – Innovative Hybrid Electro-Optic Connector
Dave Pye, SEACON’s Renewable Energy Business Development Manager gave a presentation at the International Tidal Energy Summit held in London, the UK from 26th to 27th November, titled ‘Lowering the Cost of Connection – Innovative Hybrid Electro-Optic Connector’.
MARINE ENERGY SUBSEA HUB – Low Cost Retrievable Hub for the Wave and Tidal Sector
OVERALL CONCEPT – INITIAL SCHEMATIC
To improve the viability of tidal & wave projects a subsea connection hub solution is required to reduce CAPEX, OPEX and increase availability. Current options of surface piercing platforms or heavy hubs are unsuitable & too expensive.
SEACON (europe) Ltd’s involvement in the project centres on the production of a HYBRID wet-mateable connector incorporating both high power electrical and optical fibre elements.
The aim of the SEACON project is to reduce the present cost of the separate electrical and fibre optic connectors by a significant amount.
Wet-mate electrical connectors are presently available from 4 or 5 suppliers with ratings up to 11kVAC and 400 amps or more.
Wet-mate optical connectors are presently available from a similar number of suppliers with fibre counts up to 48.
Configurations of both types include Diver mate / ROV mate and Stab plate.
To date however no HYBRID medium voltage connector has been designed and qualified to include both elements.
The environment in which these products have to survive and function is far more severe than deep water. Factors affecting performance and service life include :
a. Corrosion. Shallower deployments often result in warmer waters. High tidal flows will refresh the oxygen content in the water.
b. Marine Growth / biofouling. Again the above factors greatly increase the rate of marine growth.
c. Cyclic pressure. Wave effect can impose cyclic pressures. At a mean water depth of 50 metres, a 5 metre wave would vary the pressure from 30 to 50 psi at irregular intervals. This is not
significant in deep water.
d. Cyclic power level. In Tidal applications the power generated will vary from zero to maximum twice per day. Wave applications could generate random power levels.
e. Scour and material deposition.
Corrosion and biofouling examples :
CORROSION AND BIOFOULING TESTING
SEACON have commissioned PLYMOUTH MARINE LABS to carry out a long-term corrosion and biofouling test on various material samples.
The frame was installed by EMEC at their FALLS OF WARNESS site in late September 2013 and will be retrieved for initial examination in 6 months time.
Materials fitted to the frame include 4 metallic and two non-metallic discs, up to 10 of each type.
THE NEW PRODUCT
The product under development by SEACON as part of the TSB-funded project will have the following ratings and design features :
1. Electrical rating will be 6.6kV (u) and 250 amps per contact. 4 electrical contacts will be provided to allow for one to be used as an earth if necessary. This will allow the connector to be used on generators up to 2.5MW at 6.6kV.
2. Minimum of 4 fibre-optics. Low insertion loss (0.5db max) and single or multi-mode.
3. Stab-plate and ROV-mate variants.
4. Materials selected for maximum corrosion resistance and resistance to marine growth.
LOWERING THE COST
The aim of the project is to reduce the cost of the connectors and connection system requirements significantly. We will aim to achieve this in a number of ways:
a. Combining the two elements into one connector will mean only one set of shell components is required.
b. The “real-estate” required on the hub or generators is greatly reduced.
c. Careful material selection will result in extended lifetime and hence reduced maintenance or retrieval requirements.
d. Use of proven electrical and optical elements.
e. Provision of automatic protection for the pin half of the connector will remove the need for expensive dummies and their fitting and removal.
f. Standardised testing, in particular FAT. Here we would encourage a JIP to be set up to determine these requirements.
g. IEC TC-114: Marine energy – Wave, tidal and other water current converters.
The standards produced by TC 114 will address:
• System definition
• Performance measurement of wave, tidal and water
• Current energy converters
• Resource assessment requirements, design and survivability
• Safety requirements
• Power quality
• Manufacturing and factory testing
• Evaluation and mitigation of environmental impacts
This TSB-funded project has a timescale of 2 years. The project was initiated in February 2013 hence is scheduled to be complete in February 2015.
The connector will be completed before that date in order for it to be incorporated into the Hub.
SUMMARY & CONCLUSIONS
The product will have a rating of 6.6kV (u) and 250 amps (4-pins). Optically it will contain a minimum of 4 fibres with insertion losses of less than 0.5db. Initial depth rating will be at least 100 metres, probably more.
The aim of the SEACON element of the project is to produce a Hybrid Opto-Electric Wet-Mate connector at around 50% of the cost of two separate connectors. ROV and Stab-plate versions will be designed.
The design will incorporate materials and design features to minimise the effect of marine growth and corrosion.
As the cost of connectors is a very significant part of the overall system cost, it is hoped that this project will go a long way towards helping with the necessary cost reductions required by the Marine Renewable Energy industry.