Abstract:
A method of installing an off-shore tidal hydroelectric turbine generator is described. The method provides for a number of safety features, ensuring that all components are safe to handle during the installation operation, and also ensuring that the turbine will not start spinning during the installation operation.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method of safely installing a sub sea tidal hydroelectric turbine generator. 
     BACKGROUND OF THE INVENTION 
     The increased interest in environmental awareness, and a reluctance to rely on non-renewable sources of energy, has led to greater usage of renewable energy systems, e.g. solar power, wind power, thermal power, and tidal power. The latter involves the installation of turbine generators in an area of tidal flow, and converts the energy of the tides into electrical power. 
     With reference to  FIG. 1 , a direct-drive shaftless permanent magnet hydroelectric turbine generator is described in PCT Application No. PCT/EP2007/006258. The generator  10  comprises a ring-shaped stator  12  and a rotor  14 , the stator  12  having a plurality of coils (not shown) located about the circumference of the stator  12 . The rotor  14  comprises an inner rim  16 , which defines an open centre. The rotor  14  further comprises an array of generally radially extending blades  18  captured between the inner rim  16  and an outer rim  20 . The rotor  14  further comprises an array of magnets (not shown) disposed about the outer rim  20 . The stator  12  concentrically surrounds the rotor  14 , with the plurality of coils providing a magnetic flux return path for the magnets. 
     The generator  10  is positioned in an area of tidal flow, such that the motion of the seawater through the generator  10  acts on the blades  18 , resulting in rotation of the rotor  14  within the stator  12 . The motion of the magnets relative to the coils of the stator  12  causes the magnetic field generated by the magnets to induce an EMF in each of the coils. These induced EMFs provide the electrical power output from the turbine generator  10 . 
     In the interests of accepted good practice, it is understood that certain safety rules should be followed when undertaking the installation and connection of high voltage electrical equipment, e.g. the equipment should be switched out from all possible points of supply; isolated from all possible points of supply; safeguarded by safety padlocks being applied at switch points; and connected to earth by circuit main earths. 
     While the above criteria can be easily adhered to when dealing with above sea electrical equipment, the problem associated with isolation of an underwater turbine generator largely comes from the inaccessibility of switchgear, and the need to energise and de-energise the turbine generator from a significant distance away (e.g. from an on-shore power substation). 
     It is therefore the object of this method patent to provide a method for installing and connecting a hydroelectric turbine generator that provides certainty and safety, and reduces the operations required in potentially hazardous conditions. 
     SUMMARY OF THE INVENTION 
     Accordingly, there is provided a method of installing a sub sea tidal hydroelectric turbine generator and connecting the turbine generator to a supply grid using a submarine power cable, wherein the hydroelectric turbine generator comprises an electrical braking system operable to apply an electrical brake to the turbine upon interruption of a control signal, wherein the control signal is transmitted from a controller at a connection point to said supply grid through said submarine power cable, the method comprising the steps of:
         (i) laying a submarine power cable into position, the submarine power cable extending from a first end, at a connection point to a supply grid, to a second end, at an installation site where it is desired to install a sub sea tidal hydroelectric turbine generator;   (ii) connecting the submarine power cable to the connection point;   (iii) switching the submarine power cable out from the supply grid using a supply switch;   (iv) isolating the submarine power cable from the supply grid using an isolating switch, connecting the power cable to earth;   (v) applying a safety padlock to the supply switch and the isolating switch;   (vi) interrupting the control signal at said controller by opening a control switch, applying an electrical brake to the turbine generator;   (vii) applying a safety padlock to the control switch;   (viii) deploying said hydroelectric turbine generator at said installation site;   (ix) connecting the submarine power cable to said hydroelectric turbine generator;   (x) removing the safety padlock from to the supply switch and the isolating switch;   (xi) disconnecting the power cable from earth using the isolating switch;   (xii) switching the power cable on to the supply grid using the supply switch;   (xiii) removing the safety padlock from the control switch; and   (xiv) closing the control switch, such that the electrical brake is removed from the turbine generator, and allowing the generator to commence generation.       

     As the turbine generator is being lowered into position on site, it is impossible for the turbine to start spinning during installation. This is because the latched contactor cannot change state without a supply signal, which can only be applied through the submarine power cable, the cable remaining unconnected to the turbine generator until after the generator has been deployed. Also, the electrical braking system of the turbine generator requires the receipt of a control signal before the electrical brake can be released from the turbine. As the control signal is transmitted via the submarine power cable, it is impossible for the brake to be released without the power cable being connected to the generator. Thus the installation personnel can be assured that the turbine will not start spinning while the generator is being deployed. Furthermore, as the submarine power cable is switched out and isolated from the main supply grid, installation personnel can safely handle the power cable during the installation operation as it is not live. 
     Preferably, the method further comprises the step of testing that all sub sea circuits are dead, prior to step (ix). 
     It is important from a safety aspect that it is certain that all sub sea circuits are dead and are securely cut off from the supply before deployment of the generator, to ensure that there is no danger of electrical shocks and/or movement of the turbine during installation. 
     Preferably, steps (ii)-(viii) and (xi)-(xvi) are performed at said connection point. 
     As the majority of the steps can be performed remote to the installation site of the turbine generator, this reduces the number of steps that must be performed at the off-shore site, and correspondingly reduces risks associated with operating in variable weather conditions. 
     Preferably, the method further comprises the steps of:
         (a) recording a location designation associated with the second end of the submarine power cable once the power cable has been switched out and isolated; and   (b) prior to step (ix), verifying that the turbine deployment is occurring at the location designation associated with the second end of said particular submarine power cable.       

     The implementation of a dedicated verification step means that the turbine generator will only be deployed at the correct location, and ensures that the installation operatives will not be connecting the turbine generator to a potentially live submarine power cable. 
     Preferably, said location designation comprises GPS co-ordinates. 
     Preferably, the method further comprises the steps of:
         (a) closing a latched contactor on the hydroelectric turbine generator to connect the positive and negative output terminals of the hydroelectric turbine generator to earth prior to deploying said hydroelectric turbine generator at said installation site; and   (b) after the deployment of said hydroelectric turbine generator at said installation site, opening the latched contactor to disconnect the output terminals of the hydroelectric turbine generator from earth.       

     Preferably, step (ix) further comprises deploying said hydroelectric turbine generator at said installation site such that the axis of the turbine is aligned with the direction of the prevailing tidal current at said installation site. 
     As the turbine generator is aligned with the tidal current, this provides for the optimum performance of the turbine at the installation site. 
     Preferably, the hydroelectric turbine generator comprises a generator cable for connecting the generator to a submarine power cable, and wherein step (x) further comprises recovering the second end of said submarine power cable and said generator cable to an installation vessel for connection, wherein the submarine power cable and the generator cable act to stabilise the installation vessel in position at said installation site. 
     The submarine power cable and the generator cable of the installed generator provide a mooring facility for the installation vessel, helping to stabilise the installation site at the off-shore location. 
     There is also provided a method of installing an array of hydroelectric turbine generators, comprising the steps of installing a single hydroelectric turbine generator as described above, wherein the hydroelectric turbine generator further comprises an expansion cable for connecting to a further hydroelectric turbine generator, such that a plurality of hydroelectric turbine generators can be daisy-chained together, and wherein the method further comprises the steps of:
         (a) deploying a successive hydroelectric turbine generator at a successive installation site;   (b) connecting the expansion cable of the preceding hydroelectric turbine generator to the generator cable of the successive hydroelectric turbine generator; and   (c) repeating steps (a) and (b) for each of the hydroelectric turbine generators in the array, wherein steps (a)-(c) are performed prior to steps (xi)-(xvi).       

     As the hydroelectric turbine generators can be daisy-chained together in series, the installation of an array of turbines is carried out with the entire string of turbines isolated, earthed and locked. The entire array of turbines is then energised together. 
    
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
       An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is an isometric view of a prior art hydroelectric turbine generator; 
         FIG. 2  is an outline of a sample configuration used for the installation and connection of a hydroelectric turbine generator to a supply grid; 
         FIG. 3  is a view of an installation vessel and a hydroelectric turbine generator prior to deployment at an installation site; and 
         FIG. 4  is a view of an installation vessel and a hydroelectric turbine generator after deployment at an installation site. 
     
    
    
     With reference to  FIG. 2 , an overall view is presented of a sample circuit scheme for the installation of a hydroelectric turbine generator  10 . The generator  10  is installed at an installation site in an area of tidal flow, the generator  10  being provided on a seabed mounted support structure  22 . The generator  10  further comprises a generator cable  24 , operable to connect a generator  10  with a submarine power cable, the generator cable  24  comprising the appropriate power lines for connection to the output terminals of the generator  10 . 
     The generator  10  may further comprise an expansion cable  26 , the expansion cable  26  comprising a further set of power lines coupled to the power lines of the generator cable  24 , the expansion cable  26  allowing for a series of separate generators  10  to be daisy-chained together, so that the output of a series of generators  10  can be connected to a single submarine power cable. 
     The generator  10  comprises a set of mechanically latched two pole DC contactors  28 , the contactors  28  connected between the generator&#39;s  10  positive output and earth, and between the generator&#39;s  10  negative output and earth. The contactors  28  are controlled by a DC control wire  30 , the input to the DC control wire  30  received from the generator cable  24 . 
     The generator  10  may also comprise an electrical braking system (not shown), the electrical braking system operable to apply a short circuit across at least a portion of the coils in the generator  10 , in order to apply an electrical brake to the turbine and to prevent rotation of the turbine. The electrical braking system is actuated by a control signal received from the generator cable  24 , such that if there is an interruption to the supply of the control signal the electrical brake is applied. 
     An on-shore substation is indicated generally at  32 . The substation  32  comprises a connection  34  to a voltage source, e.g. a supply grid. The substation also comprises a plurality of controller  36 , the controllers  36  operable to generate control signals for the generators  10 . 
     The substation  32  is connected to a submarine power cable  38 . The cable is laid from a first point at the substation  32  to a second point where it is desired to install the generator  10 . The cable  38  comprises power core lines to transmit power generated by the generator  10 , and at least one control wire for the transmission of control signals from the substation  32  to the generator  10 . The power cable  38  is connected to the substation  32 . 
     The substation  32  further comprises supply switches  40  connecting the power lines of cable  38  with the voltage source connection  34 , and isolation switches  42  connecting the power lines of cable  38  with earth. 
     The substation  32  further comprises a controller voltage source  44  operable to provide power to the controllers  36 , the controller voltage source  44  connected to the controllers  36  via a controller supply switch  46 . 
     In preparation for turbine deployment and connection, the mechanically latched contactor  28  is set in the closed position, connecting the generator&#39;s  10  positive and negative output terminals to earth. The latched position of this contactor is tested and verified by the senior authorised electrical person (SAEP) for the installation operation, who will be responsible for the upcoming offshore electrical works. 
     Prior to deployment, the supply switch  40  should be opened, and the isolation switch  42  should be closed. This operation is witnessed by the SAEP. These two switch arrangements are then secured with a safety padlock, and possession of the key is retained by the SAEP. 
     Prior to deployment the controller supply switch  46  for the controllers  36  is also opened, and padlocked in place. The key for this lock should be also be retained by the SAEP. 
     The SAEP shall ensure that all sub sea circuits are dead, by using a calibrated voltage testing device while at the on-shore substation. 
     Only when the SAEP is satisfied with the turbine generator isolation arrangement (by the closing of the contactor  28  and the cutting of the supply to the controllers  36 ), the onshore substation isolation (by the opening of the supply switch  40  and the closing of the isolation switch  42 ), and has possession of all the keys of the safety padlocks can offshore operations commence. The SAEP is required to give approval for departure once they are satisfied with the above. 
     Prior to departure, the SAEP records location information regarding the end of the submarine power cable  38  that has just been disconnected from the supply and isolated. 
     With reference to  FIG. 3 , once the installation site  52  is reached, the SAEP is responsible for verifying that the GPS coordinates of the installation vessel  50  coincide with the co-ordinates of the recorded position of the particular cable end that was isolated above. Once this has been verified, the deployment of the turbine generator  10  at the installation site  52  may commence. 
     The turbine generator  10  is deployed with the mechanically latched contactor  28  in the closed position. The SAEP and working party can be safe in the knowledge that it is impossible for the turbine generator  10  to start spinning during deployment, due to the fact that the submarine power cable  38  is not connected, and therefore it is impossible for the contactor  28  to change state, or for the electrical brake to release. This serves a similar function as the onshore padlocks. 
     With reference to  FIG. 4 , the generator  10  and the support structure  22  are lowered to the seabed  54  with the generator cable  24  and the extension cable  26  being paid out under tension from the deck of the turbine deployment vessel  50  as described in  FIG. 3 . Once the turbine generator  10  is positioned on the seabed  54 , the vessel  50  begins to lay out the two cable tails  24 , 26 . The ends of the cables  24 , 26  are deployed with a clump weight (not shown). The ends of the cables can be handled with no risk of becoming electrically live, as it is impossible for the latched contactor  28  to change position, or for the electrical braking system to disengage, without a supply. Supply is not available until the cable  38  is completely connected to the generator cable  24  and unlocked back at the on-shore substation  32 . The contactors  28  also connect the generator cable  24  (and therefore the extension cable  26 ) to a local earth point, so the cables  24 , 26  are well earthed. 
     The end of the submarine power cable  38  and the end of the generator cable  24  can then be recovered to the deck of the cable installation vessel  50 , and joined to connect the generator cable  24  to the on-shore substation  32 . The generator cable  24  is safe to handle during this jointing procedure, as it is not possible to make it live until the cable joint has been complete. Further reassurance is provided by the fact that the supply to the submarine power cable  38  is padlocked in the open position (supply switch  40 ), and the key for this lock is in possession of the SAEP in charge of the cable connection. 
     Since the turbine generator axes are aligned with the current, during the cable jointing operation the vessel  50  will be aligned with the current, with twin cable catenaries spread from her stem. The generator cable  24  and its attachment to the tidal turbine support structure  22  will be of sufficient strength to allow it to be used to provide significant mooring force. Without exceeding the maximum allowable tension on the cables, the two cable catenaries of the generator cable  30  and the submarine power cable  24  will provide a reference and stabilising effect to assist vessel positioning which is generally a high risk factor when carrying out jointing operations in high-energy tidal sites. 
     Once the cable joint is completed, the ends of the two cables  38 , 24  will be lowered to the seabed  54 . 
     The offshore operation is now completed. The turbine generator  10  can now be commissioned and made live from the on-shore substation  32 . The SAEP returns to the on-shore substation  32 , and all safety padlocks are removed. 
     The isolation switch  42  is opened, disconnecting the power cable  38  from earth. The supply switch  40  is closed, connecting the power cable  38  to the load. The controller supply switch  46  is turned on. It is now possible to release the sub sea mechanically latched contactor  28  using the appropriate controller  36 . Once the sub sea switch  28  state is changed, the electrical brake is released, and generation can commence. 
     Through use of an earth return circuit on the control coil of the contactor  28  only one control wire is needed per turbine generator  10 . It will be noted that there are a limited number of control wires in a submarine power cable  38  and therefore a limited number of turbine generators  10  that can be fitted onto a single submarine power cable  38 . By use of an earth return circuit for control, it effectively doubles the number of turbine generators  10  able to be controlled from a single power cable  38 . Also, the voltage drop is halved, as the earth return circuit resistance is very small due to the large support structure  22  immersion in sea water. A continuous flow of control current may lead to corrosion over time or navigational interference. The use of a latched contactor  28  means control signals can be pulsed through the earth, and therefore has no impact on corrosion or the environment. 
     A second turbine can be added to the array at a later date using the same method as detailed above. The entire turbine string will need to be isolated, earthed and locked before a second turbine can be added. The entire string of turbines is then energised together.