Theoretical and experimental investigations into umbilical cables for communications under the sea

Continual advances are being made in the control and monitoring of subsea oil wells by the application of new technology for sensors, subsea processing and communications devices. With these advances, the demands on the subsea umbilical are constantly increasing with deployment lengths and depths growing and the quantity of controlled functions now greater than ever. The need for a good understanding of the effects of deployment subsea is essential, as communications frequencies and data throughput constantly increase. This research aims to address some of the issues regarding umbilical modelling and sets up a series of tests to measure the effects of pressure and cable flooding within the umbilical and assesses the effect of steel tubes, hydraulic hoses and cable armouring on the operating parameters of the cables. In addition, the cables are modelled using electromagnetic field solver tools and the results compared with those measured. Once prediction losses have been established, these are compared with measurements taken on the full lengths of umbilical and the reasons for any discrepancies examined. It is shown that, in a typical subsea umbilical, the proximity of conducting cores to adjacent components, such as hydraulic hoses or steel wire armour, the flooding with sea water and the pressure due to the depth of deployment all have a significant impact on the impedance parameters of the cables. The effect of cable screening on attenuation is also examined and it is shown that, as well as affecting capacitance and conductance, the screen has a significant impact on the cable resistance and inductance, with the resistance rising to a maximum at a certain screen thickness before a subsequent reduction. This effect was investigated further by modelling with an electromagnetic field solver and a possible explanation for this effect is proposed. Comparison of the modelled data and measurement of cables under the various operating conditions investigated show good correlation with the results, allowing very accurate prediction of the effects on electrical performance of cables when deployed subsea in Subsea Control System umbilicals.