Long step out direct electric heating assembly

Abstract

A subsea direct electrical heating assembly adapted to heat a hydrocarbon conducting steel pipeline ( 1 ) arranged subsea. The assembly comprises a direct electrical heating cable ( 3 ) extending along and being connected to the steel pipeline ( 1 ) and a power transmission cable ( 7 ) receiving electric power from a power supply ( 5 ) which is arranged onshore or at surface offshore, and which feeds the direct electrical heating cable ( 3 ). The subsea direct electrical heating assembly comprises a power conditioning arrangement ( 100 ) arranged at a subsea location, in a position between the power transmission cable ( 7 ) and the direct electrical heating cable ( 3 ). The power transmission cable ( 7 ) extends from the offshore or onshore power supply ( 5 ) and down to the power conditioning arrangement ( 100 ).

1 . A subsea direct electrical heating assembly adapted to heat a hydrocarbon conducting steel pipeline arranged subsea, the subsea direct electric heating assembly comprising:
 a direct electrical heating cable extending along and being connected to the steel pipeline and a power transmission cable receiving electric power from a power supply, arranged onshore or at surface offshore, and feeding the direct electrical heating cable;   a power conditioning arrangement arranged at a subsea location, in a position between the power transmission cable and the direct electrical heating cable; and   wherein the power transmission cable extends from the offshore or onshore power supply and down to the power conditioning arrangement.   
     
     
         2 . A subsea direct electrical heating assembly according to  claim 1 , wherein the power conditioning arrangement comprises a subsea capacitor arrangement. 
     
     
         3 . A subsea direct electrical heating assembly according to  claim 1 , wherein the power conditioning arrangement comprises a transformer. 
     
     
         4 . A subsea direct electrical heating assembly according to  claim 1 , wherein the direct electrical heating cable is arranged along and attached to the pipeline. 
     
     
         5 . A subsea direct electrical heating assembly according to  claim 1 , wherein the subsea direct electrical heating assembly is adapted to heat a plurality of pipeline sections which each constitutes a part of a longer pipeline as the direct electric heating assembly comprises a plurality of direct electric heating cables arranged along and/or in proximity to the pipeline sections and that for each pipeline section a said power conditioning arrangement is arranged between the power transmission cable and the section heating cables associated to each pipeline section. 
     
     
         6 . A subsea direct electrical heating assembly according to  claim 1 , wherein power from said power transmission cable is fed to a direct electrical heating cable adapted to heat a pipeline extending between a subsea well and a compression facility, through the subsea power conditioning arrangement. 
     
     
         7 . A subsea direct electrical heating assembly according to  claim 2 , wherein the subsea capacitor arrangement is in the kV and kVAr range or above, comprising a capacitor element arranged within a tank that prevents sea water entering the tank, wherein the tank is pressure balanced and filled with a pressure compensation fluid. 
     
     
         8 . A subsea direct electrical heating assembly according to  claim 3 , wherein the transformer is arranged within the tank. 
     
     
         9 . A subsea direct electrical heating assembly according to  claim 7 , wherein the capacitor arrangement is a variable capacitor arrangement, the capacitance of which is adjustable between an upper and lower value by means of an actuator arranged within the tank. 
     
     
         10 . A subsea direct electrical heating assembly according to  claim 3 , wherein the transformer is an adjustable transformer. 
     
     
         11 . A subsea direct electric heating assembly according to  claim 3 , wherein the power transmission cable comprises three phases and that three section heating cables are each connected between a different pair of phases. 
     
     
         12 . A subsea direct electric heating assembly according to  claim 11 , comprising three sets of section heating cables, wherein each set comprises two or more section cables. 
     
     
         13 . A subsea direct electric heating assembly according to  claim 8 , wherein the power conditioning arrangement is connected between the power transmission cable and a midpoint fed pipeline section, wherein two transformer terminals exit the tank through penetrators and are connected to respective ends of said pipeline section, and that a third transformer terminal is connected to a section midpoint connection cable that connects to a midpoint on the pipeline section between said respective ends, wherein the section midpoint connection cable is short circuited to a steel structure of the power conditioning arrangement as is also the third transformer terminal. 
     
     
         14 . A subsea direct electric heating assembly according to  claim 1 , wherein the power transmission cable extends at least 30 km between the power supply and said power conditioning arrangement. 
     
     
         15 . A subsea direct electric heating assembly according to  claim 1 , wherein the power conditioning arrangement is connected to a plurality of DEH cables which are arranged along different pipelines. 
     
     
         16 . A subsea direct electric heating assembly according to  claim 1 , wherein the power conditioning arrangement is connected to a plurality of sets of a plurality of DEH cables, wherein each set is arranged to heat a plurality of parallel pipelines.