Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 10 replies
  • Subscribers 9 subscribers
  • Views 440 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Current profile of subsea export cables

Sig
From the offshore substation, why would the current profile slope down towards the middle of the export cable then rise again at it's terminal end (onshore substation)? Is it because at both ends of the export cable, there is effectively a 'source'? One would have expected the current from one end to the other to have a linear drop off (heat and other losses).Wondering if charging current has a play into this also. 



See attached graph.



Thanks
Parents
  • 0
    AC, good, this curve may be a correct if there is VAr compensation applied at the ends, but unequally - in effect there is shunt inductance to tune out, or resonate with (i a very low Q way) the line capacitance. This can result in the voltages at the two ends not being the same, and therefore the capacitive displacement currents vary along the cable.


    In effect the core to armour capacitance of the cable is not fully compensated by the self inductance for the desired load impedance. On long cables it is possible to put lumps of compensation part way along, but undersea is not practical unless there is already a handy island part way along the route. ? . At 50Hz high power uncompensated lines get tricky after about 50km or so, but how much is tolerable is a function of the voltage in use, and the power to be transmitted - 50A into capacitance is no biggy if the load is 1000A. if the load is a few hundred Amps however, it matters that much more.

    DC lines have no such issue - a volt in at one end, comes out as a volt at the other, eventually.
Reply
  • 0
    AC, good, this curve may be a correct if there is VAr compensation applied at the ends, but unequally - in effect there is shunt inductance to tune out, or resonate with (i a very low Q way) the line capacitance. This can result in the voltages at the two ends not being the same, and therefore the capacitive displacement currents vary along the cable.


    In effect the core to armour capacitance of the cable is not fully compensated by the self inductance for the desired load impedance. On long cables it is possible to put lumps of compensation part way along, but undersea is not practical unless there is already a handy island part way along the route. ? . At 50Hz high power uncompensated lines get tricky after about 50km or so, but how much is tolerable is a function of the voltage in use, and the power to be transmitted - 50A into capacitance is no biggy if the load is 1000A. if the load is a few hundred Amps however, it matters that much more.

    DC lines have no such issue - a volt in at one end, comes out as a volt at the other, eventually.
Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines