Trw Limited

Trw Systems and Energy

Walter B Warren

Ronald Jon Marosko

Marvin Fox

Donald L Cooper

This invention relates to the distribution of electrical power to subsea petroleum recovery installations, and more particularly to methods and apparatus for sensing and limiting the electrical current drawn through power cables disposed on the sea floor. A transformer having primary winding and a secondary winding is located at a subsea power distribution module and has its primary winding connected in series with the power cable. A variable impedance device is connected to the secondary winding and is actuated, in response to a control signal indicative of the current drawn through the power cable, to substantially open-circuit the secondary winding when the current exceeds a predetermined value. Additionally, the variable impedance device substantially short-circuits the secondary winding when the load current falls to a level less than a preselected minimum value. In a preferred embodiment, the invention is utilized in a polyphase power system, and the variable impedance device employs a solid state device that may be switched by a bi-stable control signal to produce either the high impedance condition or the low impedance condition. When the current requirement of the load returns to a normal operating range, the variable impedance device will automatically close and the impedance of the transformer will return to its normally low value. It is a particular feature of this invention to provide methods and apparatus for limiting the current supplied to inductive cable coupling devices employed in subsea petroleum installations.

Methods and apparatus for limiting electrical current to a subsea

A hydrocarbon detection system is provided for use in a subsea hydrocarbon production installation which includes production tree assemblies, an electro-hydraulic control module located on the sea floor and remote from the production trees, cable assemblies interconnecting the control module with the production trees through magnetic coupling devices. A pair of inductive elements are electrically coupled by the surrounding sea water. Displacement of the conductive sea water by escaping hydrocarbons affects the coupling between the inductive elements to produce a hydrocarbon-presence-responsive output signal. The inductive elements are resonated within a selected frequency range by capacitors coupled with a primary inductor coil by auxiliary windings on a common core element. An excitation signal sweeps over the selected frequency range at a rate effective to produce a peak detected signal at the resonant frequency. The peak output signal is then monitored to form a control signal functionally related to the presence or absence of hydrocarbons in the sea water.

Subsea hydrocarbon sensor system

The relative horizontal positions of a floating marine platform and the lower end of a flexible connecting line, such as a cable, drill string, or well bore riser, suspended from the platform are determined by generating angle signals representing the instantaneous vertical slope angles of the connecting line at or near its upper and lower ends, filtering these signals to remove higher order frequencies resulting from variable forcing functions, such as surface wave induced motion of the platform, which produce no net change in the platform position, whereby the filtered angle signals represent the mean terminal slope angles of the envelope of the undulating connecting line, and combining these filtered angle signals in accordance with a predetermined position equation which compensates for phase lag between the sensor measured and true positions of the platform due to the transit time of platform motion induced stress waves or undulations along the connecting line to the lower angle sensor. The invention is described in the context of positioning a floating oil well drilling or producing platform relative to an ocean floor well head.

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Seabrook, TX, United States of America

Walter B Warren