Patent Publication Number: US-8122841-B2

Title: Device and a method of connecting an electrical power line between a ship and a terminal

Description:
This application is a §371 national phase filing of PCT/FR2007/050967 filed Mar. 20, 2007. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of connecting an electrical power line between a ship and a terminal. More particularly, it relates to connecting an electrical power line between a methane tanker and a gas terminal. 
     BACKGROUND OF THE INVENTION 
     It is known to connect an electrical power line between a ship and a port, e.g. in the manner presently in use for connecting a cruise ship to a local electricity mains network in order to avoid the ship running its generator unit while in port. 
       FIG. 9  is a highly diagrammatic view of a prior art device for connecting an electrical power line between a ship and a port. 
     The device comprises a power line  101  constituted by one or more cables terminated by one or more connectors  115 . The power line  101  is supported via collars  116  by suspension lines  118  and systems  120  that can be moved on a crane  122 . 
     That device thus serves to connect an electricity switchboard  117  to the local electricity network in the port  5 . To make the connection, once the ship  3  has docked, and the power line  101  has been brought up to the ship  3 , the crew makes use of one or more heaving lines  124  to bring the connector  115  of the power line  101  on board, and then take it to the switchboard  117 . The connector  115  is connected to the switchboard  117  manually. 
     Nevertheless, that connection device presents several drawbacks. 
     The connection operations can be lengthy (typically more than one hour) and difficult, or even dangerous for the crew, or impossible under adverse weather conditions. 
     In addition, that kind of connection is not compatible with the security requirements that apply to methane tankers and terminals, in particular because of the need to be able to disconnect rapidly, and also because the power lines need to be isolated from the surroundings since the surroundings can be explosive. 
     Furthermore, the electrical power that can be transferred via that type of connection is limited, typically to less than 15 megawatts (MW), whereas the power installed on a methane tanker can be as much as 30 MW. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The present invention thus seeks to mitigate the above-mentioned drawbacks by proposing a method and a device for safely and quickly connecting an electrical power line between a ship and a terminal. 
     These objects are achieved by a device for connecting an electrical power line between a ship and a terminal, the device comprising:
         unwinder means for unwinding a traction cable from the ship towards a connection end of said electrical power line;   lashing means for lashing said traction cable to said connection end; and   traction means for pulling said electrical power line towards the ship so as to connect said connection end with an electrical interface of the ship.       

     Thus, the power line can easily be taken by the traction cable from a storage zone beside the terminal for connection to the electrical interface of the ship. In addition, emergency disconnection can be achieved in simple manner by unwinding and then letting go of the end of the traction cable, thereby completely releasing the ship from the terminal. 
     In an aspect of the invention, the connection device includes float means for maintaining at least a portion of said power line below the surface of the water. 
     By being under water, the power line is not exposed to the risks of performing operations in an atmosphere that is potentially explosive. Thus safety is entirely compatible with the safety requirements that are applicable in particular to methane tankers and terminals. 
     The connection device may include return means for returning the power line towards the terminal when said power line is disconnected from the ship and the traction cable is released. 
     The power line can thus easily be brought back to its storage zone. 
     Advantageously, the connection device includes guide means for guiding said connection end towards said electrical interface so as to provide electrical coupling between the ship and the terminal. Thus, the connection can be made automatically. 
     Furthermore, the connection device can include a barge for supporting a terminal portion of the power line including said connection end, said barge including protection means for bearing against the hull of the ship. 
     Thus, the power line can be brought to the vicinity of the ship in order to be connected in a manner that is simple and quite safe. 
     Advantageously, the hull of said barge may include an opening enabling said terminal portion of the power line to be stored beneath the barge. 
     Thus, supporting the power line is made easier and safety is increased. 
     In a particular aspect, said terminal portion of the power line is stored on the barge and includes a double-walled covering. 
     Thus, the overhead portion of the power line can be protected from risks due to a potential explosive atmosphere. Furthermore, the double-walled covering enables the electrical conductors of the power line to be cooled by a fluid (e.g. water). 
     According to another particular aspect, said barge includes a caisson including gaskets surrounding the above-water portion of the power line and co-operating with the hull of the ship, with the hull of the barge, and with the water surface to form a zone that is airtight relative to the outside. 
     This makes it possible to isolate the above-water portion of the power line from the potentially explosive atmosphere, thereby increasing safety while making a connection. 
     Advantageously, the connection includes a blower located on the ship or the barge, for raising the pressure in said airtight zone, said blower taking air from a gas-free zone. Safety is thus further improved. 
     The connection device may include a source of inert gas for filling said airtight zone with inert gas. 
     The traction means may comprise a winch located on the ship for using the traction cable to pull the connection end of said power line. 
     Advantageously, the traction means include suspension means for compensating the weight of said power line. 
     The invention also provides a ship including an electrical interface for coupling electrically to a terminal, the ship comprising:
         unwinder means for unwinding a traction cable towards a connection end of an electrical power line connected to the terminal;   lashing means for lashing said traction cable to said connection end; and   traction means for pulling said electrical power line towards the ship in order to connect said connection end with said electrical interface.       

     In an embodiment, the hull of the ship includes a duct for passing the power line, said duct opening out below the water line. 
     Thus, by opening out below the water line, the duct serves to protect the power line from any explosive atmosphere. 
     Advantageously, the end of the traction cable includes a submersible buoy. 
     Thus, once it has gone through the opening of the duct, the end of the traction cable can easily be returned to the surface where it can be connected to the connection end of said power line. 
     In another embodiment, the hull of the ship includes a duct for passing the power line and opening out beneath the water line, and the duct is extended by a gastight covering. 
     Advantageously, said duct includes a watertight protection hatch. 
     Advantageously, the ship includes guide means including docking means for guiding said connection end of said power line towards socket means of the electrical connection interface. This enables the connection to be made quickly and in complete safety. 
     Said electrical connection interface may include a watertight protective cover. 
     Advantageously, the ship includes a control station that is accessible via a watertight door of the ship. 
     In particular, the ship may be a methane tanker. 
     The invention also provides an electrical coupling device comprising an electrical power line for connecting a ship to a terminal, the device comprising float means for maintaining at least a portion of said electrical power line below the surface of the water while it is being conveyed between the terminal and the ship. 
     The invention also provides a method of connecting an electrical power line between a ship and a terminal, the method comprising the following steps:
         unwinding a traction cable from the ship towards a connection end of said electrical power line;   lashing said traction cable to said connection end;   pulling said electrical power line towards the ship; and   connecting said connection end of said power line with an electrical interface of the ship in order to provide electrical coupling between the ship and the terminal.       

     Advantageously, during the traction step, at least a portion of the electrical power line is maintained below the surface of the water. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the method and the device of the invention appear on reading the following description given by way of non-limiting indication with reference to the accompanying drawings, in which: 
         FIG. 1  is a highly diagrammatic view of a device of the invention for connecting an electrical power line between a ship and a terminal; 
         FIGS. 2 and 3  are highly diagrammatic views of embodiments of the  FIG. 1  connection device; 
         FIG. 4  is a highly diagrammatic view of a terminal portion of the  FIG. 1  power line; 
         FIGS. 5A to 5D  show different steps during connection or disconnection between the ship and the terminal using the connection device of  FIG. 3 ; 
         FIGS. 6A to 6C  are highly diagrammatic views showing variants of a barge of the connection device of the invention; 
         FIGS. 7A and 7B  are highly diagrammatic views of variants of a connection zone on board the ship of the invention; 
         FIGS. 8A to 8C  are highly diagrammatic views of variants of a duct in the hull of the ship of the invention for passing the power line; and 
         FIG. 9  is a highly diagrammatic view of a prior art device for connecting an electrical power line between a ship and a terminal. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In accordance with the invention,  FIG. 1  is a highly diagrammatic view of a device for connecting an electrical power line  1  between a ship  3  and a terminal  5 . 
     The connection device comprises unwinder means  7 , lashing means  9 , and traction means  11 . 
     The unwinder means  7  are for unwinding a traction cable  13  from the ship  3  towards a connection end  15  including the connector  15   a  of the electrical power line. The power line  1  may comprise a plurality of electrical connection cables, and it may be stowed in a storage zone at the terminal  5 . It should be observed that the capacity of the electrical power line  1  for transferring electricity may be as great as 30 MW. 
     The lashing means  9  are for lashing the traction cable  13  to the connection end  15  of the electrical power line  1 . 
     The traction means  11  are designed to use the traction cable  13  to pull the electrical power line  1  towards a connection point or zone  17  of the ship  3  so as to connect the connection end  15  with an electrical interface  17   a . This enables electrical coupling to be provided between the ship  3  and the terminal  5 . 
     In addition, the electrical coupling can be disconnected quickly and simply by unwinding the free end  13  of the traction cable and then letting it go. This enables the ship  3  to be completely released from the terminal  5 . 
       FIG. 2  is a highly diagrammatic view showing an embodiment of the device for connecting the electrical power line  1  between the ship  3  and the terminal  5  in which the power line  1  is under water. 
     The electrical connection or coupling device in this example includes float means  21 , e.g. a series of floats  21 , for holding at least a portion of the power line  1  under the free surface  23  of the water while it is being transported between the terminal  5  and the ship  3 . 
     Thus, since the power line  1  is under water, it is not exposed to the risks of operating in an atmosphere that is potentially explosive, e.g. in the event of the terminal  5  being a gas terminal and/or the ship  3  being of the methane tanker type. 
     In addition, the connection device in this example includes a pilot boat  25  that corresponds to the unwinder means  7  and the lashing means  9 . 
     Thus, maneuvers performed to make the connection are as simple as those required for installing or casting off mooring lines and do not require additional crew. 
       FIG. 3  is a highly diagrammatic view of another example of a connection device that differs from the device of  FIG. 2  in that it further includes return means  27  and a barge  31 . 
     Advantageously, the return means  27  are designed to return the power line  1  to the terminal  5  when the power line  1  is disconnected from the ship and the traction cable  13  is released. The return means  27  may correspond to a return cable  27  (as shown) or to using a boat  25 , or to using propulsion means (not shown) on board the float means  21  or the barge  31 . 
     The barge  31  serves to support a terminal portion  33  of the power line  1  including the connection end  15 . Thus, the barge  31  may include support means  34  for supporting the last above-water segment of the terminal portion  33  of the power line  1 . 
     In addition, the barge  31  may include protection means  35  or fenders enabling it to bear against the hull  37  of the ship  3 . 
     The terminal portion  33  of the power line  1  as stored on the barge  31  may optionally include a double-walled covering. 
     In order to avoid risks in an atmosphere that is potentially explosive, the above-water terminal portion  33  of the power line  1  may optionally be provided with a double-walled covering  36  as shown in  FIG. 4 . In addition to creating two barriers against the outside, the double-walled covering  36  makes it possible, advantageously, to cool the electrical conductors of the power line  1  by means of water or some other fluid. 
     In a variant (see  FIGS. 6A and 6B ) the hull of the barge  31  may include an opening that enables the terminal portion  33  of the power line  1  to be stored beneath the barge  31 . In this configuration, the support means  34  can be simplified or even omitted. 
       FIGS. 5A to 5D  show various connection or disconnection steps between the ship  3  and the terminal  5  when using the connection device of  FIG. 3 . 
       FIG. 5A  shows the initial step in which the boat  25  brings the traction cable  13  from the ship  3  to the barge  31  in order to secure it to the connection end  15  of the power line  1 . 
       FIG. 5B  shows the step of pulling the barge  31  and its floats  21  supporting the under-water power line from their storage zone towards the ship  3 . The traction means  11  may comprise a winch (see  FIG. 7A ) placed on the ship  3  for pulling the connection end  15  of the power line  1  via the traction cable  13 . Thus, during the traction step, at least a portion of the electrical power line  1  is maintained beneath the surface  23  of the water. It should be observed that this step is analogous to the simple conventional operation of taking up slack in moorings. 
       FIG. 5C  shows the step of establishing electrical coupling between the ship  3  and the terminal  5 . In this step, the traction cable  13  pulls the connection end  15  of the power line  1  until the barge  31  bears against the hull  37  of the ship  3 , and the connector  15   a  is connected to the electrical interface  17   a  of the ship  3 . 
     Furthermore, disconnection or uncoupling between the ship  3  and the terminal  5  can be implemented simply, merely by releasing the connection end  15  of the power line  1  from the electrical interface  17   a  and from the traction cable  13 . Thereafter, the barge  31  and the floats  21  supporting the power line  1  can be returned towards their storage zone by the return means  27 , e.g. by the return cable  27 . In a variant, the barge  31  and the floats  21  can be returned by the boat  25  or by propulsion means (not shown) on board the barge  31 . 
     It should be observed that the connection and disconnection operations are similar to conventional mooring operations and can be performed by the pilot and crew members who perform mooring maneuvers. 
       FIG. 5D  shows a rapid disconnection step. In an emergency, once the connection end  15  has been released, the traction cable  13  can be cast off so as to allow the above-water portion of the power line  1  to drop down onto the support means  34  of the barge  31 . 
     Thus, in an emergency, the ship  3  can in a very short time (a few minutes) be released completely from the terminal  5  by unwinding and then letting go the end  13   a  of the traction cable  13 . Thereafter, the return means  27  can move the power line  1  away from the ship  3 . 
       FIG. 6A  shows a variant of the barge  31  that serves in particular to satisfy the need to isolate the above-water portion of the power line  1  from the possibly explosive atmosphere. 
     In this example, the barge  31  includes an airtight caisson  61  provided with gaskets  63 , which caisson surrounds the above-water or terminal portion  33  of the power line  1 . Thus, the caisson  61  co-operates with the hull  37  of the ship  3 , the hull  65  of the barge  31 , and the surface  23  of the water to form an airtight zone or closed volume  67  that is airtight relative to the outside. 
     Optionally, in order to obtain even more effective protection against a risk of an explosive atmosphere, it is possible to use a blower (not shown) placed on the ship  3  or the barge  31 . The blower is designed to take air from a gas-free zone so as to keep the airtight zone  67  at a slightly raised pressure. 
     Another solution would be to perform this function by using a source of inert gas, e.g. nitrogen, and filling the airtight zone  67  with the inert gas. Such inert gas can be available on board the ship  3 , or on board the barge  31 , or from the terminal  5 . 
     This example shows that the traction means  11  include a winch  45  for using the cable  13  to pull the connection end  15  of the power line  1 . 
     Optionally, the traction means  11  may include suspension means  69  for compensating the weight of the power line  1 . 
     The suspension means  69  serve to facilitate maneuvering by compensating for the weight of the power line  1  by means of a suspension system connected to a weight or springs  71 . 
     In the configuration of the  FIG. 6A  example, it is advantageous for the power line  1  to be stored under the barge  31 . 
       FIG. 6B  shows that the hull of the barge  31  is provided with an opening  73  or that the barge  31  is of the catamaran type so as to allow the power line  1  to be stored by being suspended under the barge  31 . 
       FIG. 6C  shows another variant of the barge  31  that differs from that of  FIG. 6A  solely by the fact that the barge  31  has an airtight caisson  61   a  of sufficient volume to provide protection and storage of the power line  1  inside it and out of the water. Thus, when the barge  31  is next to the ship  3  and the power line  1  is activated, the airtight caisson  61   a  can provide protection against a potentially explosive atmosphere. 
       FIG. 7A  shows in greater detail the connection zone  17  on board the ship  3 . This example shows that the connection device may include guide means  41   a  to  41   d  enabling the connection end  15  to be guided and connected to the electrical interface  17   a  of the ship  3  so as to provide electrical coupling between the ship  3  and the terminal  5  in automatic manner. 
     The connection zone  17  may correspond to an opening  43  in the hull  37  of the ship  3 , including the traction means  11  that may comprise the winch  45 , the guide means  41   a  to  41   d , the electrical interface  17   a , and a control station  47 . 
     By way of example, this figure shows that the power line  1  has two electrical cables with ends that are pulled by the winch  45  acting on the cable  13 . Naturally, the power line could comprise an arbitrary number of electric cables. 
     The control station  47  may be accessible via a watertight door  49  to allow a crew member  50  to maneuver the winch  45  for controlling a connection or disconnection operation. 
     The guide means  41   a  to  41   d  may include male and female docking means  41   b  and  41   a  that provide final mechanical guidance for the connection end  15  towards socket means  51  of the electrical interface  17   a  for connecting the connector(s)  15   a  to the socket means  51 . 
     Optionally, the guide means  41   a  to  41   d  may include an intermediate sheave  41   c  and a ramp  41   d  for facilitating guidance and centering of the connector(s)  15   a  in the socket means  51 . 
     In addition, the opening  43  in the hull  37  may be provided with a watertight closure cover  53  enabling it to be closed when the electrical interface  17   a  is inactive. 
       FIG. 7B  shows another embodiment that differs from that of  FIG. 7A  by the fact that the connection zone  17  is situated inside the ship  3 . 
     In this example, the hull  37  of the ship  3  includes a duct  81  for passing the power line  1 . This duct  81  is provided with a watertight closure hatch  54  enabling it to be closed when the electrical interface  17   a  is inactive. 
     As before, the guide means  41   a  to  41   d  may comprise male and female docking means  41   b ,  41   a  for providing final mechanical guidance to the connection end  15  towards the socket means  51  of the electrical interface  17   a  in order to connect the connector(s)  15   a  to said socket means  51 . 
     In this example, the female docking means  41   a  of the electrical interface  17   a  are disposed in such a manner as to receive the connection end  15  of the power line  1  leaving the duct  81  in a substantially vertical direction. 
       FIG. 8A  is a diagram showing a ship  3  with a hull  37  that includes a duct  81  for passing the power line  1  and that opens out below the water line  23 . 
     The power line  1  can be pulled from inside the hull  37  of the ship by the winch  45  so as to pass through the airtight duct  81 , which duct may also be put under air or nitrogen pressure by means of a blower  83 . By virtue of the opening  81   a  of this duct  81  being situated below the water line  23 , it is possible to protect the power line  1  from any explosive atmosphere. 
     It should be observed that in this configuration, the end of the traction cable  13  is provided with a submersible buoy  85  that makes it possible, once it has passed through the opening  81   a , to bring this end of the traction cable  13  to the surface where it can be connected by the boat crew to the connection end  15  of the power line  1 . 
       FIG. 8B  shows that the end  13   a  of the traction cable  13 , possibly fitted with a buoy  85 , can remain on one side of the ship  3  while it is at sea. When the connection is to be established, this end  13   a  is sent towards the boat for connection to the connection end  15  of the power line  1 , thereby enabling the power line  1  to be put into place, even when the opening  81   a  of the duct  81  lies below the water line  23 . 
       FIG. 8C  shows a variant of  FIG. 8A . In this example, the hull  37  of the ship  3  includes a duct  91  for passing the power line  1 , which duct opens out below the water line  23 . In this example, the terminal portion  33  of the power line  1  outside the duct  91  can be protected from a possibly explosive atmosphere by a flexible gastight covering  93  that extends the duct  91 , or alternatively by a caisson  61  (as shown in  FIG. 6A ) or a caisson  61   a  (as shown in  FIG. 6C ). 
     It should be observed that in the configurations shown in  FIGS. 8A to 8C , the guidance of the power line  1  is simplified since it is ensured in part by the duct  81  or  91 . 
     Thus, in accordance with the invention, the power line  1  is adapted to feed the ship  3  with electricity from the terminal  5 , or vice versa to feed the terminal  5  from the ship  3 . 
     The ship  3  (e.g. a methane tanker) may include an electricity generator (not shown) for powering the terminal  5  electrically via the power line  1 . Thus, a fraction of the energy produced by the electricity generator of the ship  3  can be fed to the gas terminal  5 . 
     Advantageously, the present invention provides electrical connection means that are as easy to put into place as a mooring. 
     These electrical connection means comprise the following advantages:
         the time required for connection and disconnection maneuvers is less than about 15 minutes;   the maneuvers are as simple as those needed for putting into place or casting off mooring lines, and do not require additional personnel;   it has the capacity to exchange electrical power of about 30 MW; and   it is compatible with the safety requirements applicable to methane tankers and terminals.