Methods and apparatus for limiting electrical current to a subsea

Abstract

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.