The present invention relates to a specially designed cable electrode system for use in a device for reduction of unwanted organisms in a marine farm comprising a corral bag. Especially the present invention relates to a cable electrode applicable as an electrode in a system for applying and electrical field to the outer perimeter of a corral bag, where the electrical field functions as a barrier against unwanted organisms such as salmon louse (Lepeophtheirus salmonis) and other parasites and at the same time reduces the fouling of the corral bag. Background

Marine farming including shellfish and fish farming in fish corrals arranged in the sea have gained much ground and interest in the resent years. Unfortunately the corrals are disturbed by many plants and organisms. Sea plants and unwanted shellfish attach themselves to the mesh and other surfaces submerged in the sea. Further parasites such as salmon louse/lice may infect the fish in the corral reducing their growth and quality.

To limit fouling copper based impregnation has previously been used but as the impregnation is worn of over time the copper is released to the environment resulting in pollution and requiring cleaning and re-impregnation which results in additional risks for the environment.

WO02/074075 discloses a method and system for preventing unwanted organisms from affecting, in a disturbing manner, marine farming facilities. The system consists of surrounding an inner electrically conductive corral bag with an external corral bag at a certain distance of the first corral bag. The external corral bag has been made electrically conductive and the inner corral bag and the external corral bag are supplied with voltage of opposite polarity. Additionally the external corral bag may in a preferred solution be surrounded by a number of electrically conductive poles pointing downwards from sea surface. The poles are supplied with the opposite voltage than the external corral bag. Prior art

WO02/074075 discloses that known methods of making corral bags electrically conductive includes weaving copper wire or coal wire into the mesh, or proofing with carboniferous material. The poles comprise a conductive material, for example copper, coated with polymer-thermoplastics to which a filler of electrically conductive material e.g. carbon powder, has been added. On a floating fish farm a path or small walk way is normally provided for inspection and maintenance of the fish corral. Also the device according to WO02/074075 would require inspection and maintenance and the safety of the personal performing any work on the fish corral should be secured also when employing a system based on supplying an electrical field.

The prior art solutions does not disclosed how the conductive mesh nor the conductive poles are to be supplied with the intended voltage in a manner safe for the personal and with the access for installation and maintenance.

Objectives of the invention

The aim of the present invention is to provide a cable solution adapted especially to the use in connection with a fish corral. The cable should be safe for inspection and installation.

A further aim is to provide a cable that is designed to tolerate being arranged submerged in sea water without losing significant efficiency over the intended lifetime.

Preferably the cables are to provide the intended electrical field and/or electrical current over a selected three dimensional area and/or as an elongated fence along, or around the fish-farm units or shellfish-farm.

The present invention provides a cable electrode comprising at least three sections: a connection section, an active section and an end section, wherein the cable electrode comprises a central conductor which in the connection section is surrounded by a electrically insulating polymer layer, in the active section the central conductor is surrounded by a polymer layer comprising a conductive filler and in the end section the conductor is surrounded by a electrically insulating polymer layer. Optionally the electrically insulating polymer layer on the end section is water tight, thereby protection the conductor from direct water contact and limiting corrosion thereof. In a preferred embodiment the cable electrode is a water submergible electrical fence cable electrode.

In one aspect of the present invention the electrically insulating water tight polymer layer covers the free end of the conductor. Thereby the conductor is protected from direct contact with the water and corrosion as a consequence of such direct contact.

In a further aspect the electrically insulating polymer layer, the polymer layer comprising a conductive filler and the electrically insulating preferably water tight polymer layer taken together fully radially surrounds the conductor at least one time. The cable electrode is accordingly from the connecting end to the free end radially covered with at least one of said polymer layers. Thereby the conductor is protected from direct influence by the water or moist air that surrounds it. In an aspect of the present invention the conductor comprises copper or copper alloys and is massive or stranded. The conductor may further be coated by nickel or silver. Further the conductor may comprise strength members made of for instance metals such as steel, polymer yarns based on e.g. polyamide, polyester, polypropylene or carbon or a combination thereof.

In one aspect of the present invention the polymer layer comprising a conductive filler has a radial conductivity measured as a current in a circuit in the Nexans test of between 0.05 to 2.0 mA..

The polymer layer comprising a conductive filler is in one aspect of the invention based on a thermoplastic polymer material selected from polyethylene and copolymers thereof, polyurethane, polyester and blends thereof.

The preparation of a polymer comprising a conductive filler is well known within the art of cable fabrication, here this type of material are normally referred to as "semiconductive" polymers. Several different compounds can be applied as the conductive filler, and any such compound may be employed here.

The present invention further relates to the use of the cable electrode in an electrical fence for a fish corral.

In one aspect the invention relates to the use of a cable electrode as a vertical conductive pole arranged outside a corral bag. Further in another aspect the invention relates to the use of a cable electrode to provide an electric conductive corral bag comprising a mesh, where the cable electrode is arranged along the mesh of the corral bag. In a special aspect a plurality of cable electrodes according to the present invention are arranged generally vertically, in parallel along, or around the mesh of the corral bag. In this aspect of the invention a power supply for connecting to the conductors within the electrodes are arranged on a part of the corral arrangement arranged near or preferably above the sea surface. From here the electrode cables run as parallel generally vertical cables into the sea. The cable electrodes can be woven into the mesh of the corral bag to secure them to the bag or they can be secured to the bag by other means. For an inner corral bag according to WO02/074075 the distance between the electrodes may be from 5 to 15 cm, whereas for an outer corral bag with a coarser mesh the distance between the electrodes can be greater, following the coarser mesh, such as between 25 to 200 cm.

In another aspect of the present invention relates to the use of a cable electrode according to the present invention to provide an electric conductive elongated fence along one or more fish farms or one or more shellfish farms. The term "corral bag" as employed here refers to a structure adapted for controlling the location of the fish, shellfish such as oysters and blue mussels as well as other animals being farmed in a marine farm. For fish farming the corral normally has a bag-like structure for other animals the corral bag may have different shapes.

Brief description of the drawings

The present invention will be described in further detail with reference to the enclosed illustrative figures where

Figure 1 is a schematic sketch of the cross sectional view a long the longitudinal axis of a cable electrode according to the present invention.

Figures 2, 3 and 4 illustrate schematically the cross sectional view across the longitudinal axis of the cable electrode of figure 1 at the levels B-B, A-A and C-C respectively.

Figure 5 illustrates a fish corral arrangement with conductive vertical poles arranged surrounding a corral bag.

Figure 6 illustrates a possible mesh structure with cable electrodes installed therein.

Figure 7 illustrates a part of a corral bag structure with included cable electrodes.

Figure 8 illustrates schematically the arrangement of a fence along a number of fish farming units. Figure 9 illustrates schematically the test upset for measuring the radial conductivity.

Principal description of the invention

Figure 1 to 4 illustrated the main structure of a cable electrode according to the present invention. Figure 1 illustrates a cross sectional view along the longitudinal axis of the cable where as the figures 2, 3 and 4 respectively illustrates the cross section of the different sections across the longitudinal axis of the cable electrode.

The cable electrode 1 comprises three sections, the connection section 2, the active section 3 and the end section 4. The length of each of the sections can be freely selected. A conductor 5 is centrally arranged within the cable electrode. In the connection section the conductor 5 is radially covered by an electrical insulating polymer layer 12. The free end of the connection section 2 is intended for connection to a voltage supply. The electrical insulating layer 12 will therefore be covering the cable in the area handled during installation and maintenance. In the active section 3 the conductor is surrounded by a polymer comprising a conductive filler. This "semi-conductive" layer together with another electrode/conductive element of opposite polarity provides a distributed electrical field acting as an electrical fence against unwanted organisms including parasites like salmon lice or fouling by plants and crustacean and other organisms present in the sea in which fish farm is situated. Accordingly the term "active" refers to active in forming the electrical field and/or current. In the end section 4 the conductor is covered by an electrical insulating polymer layer 16 which is water tight. The polymer layer 16 also surrounds the end surface 6 of the conductor and accordingly provides a free end 18 with a water tight protection of the conductor. Figure 1 illustrates that only one insulation layer is present at each section but the insulation layers may overlap the electrical insulating layers of the end section and the connection section may be arranged on an outside surface of a semi-conductive layer covering the whole or a larger part of the surface of the conductor.

The following detailed description of the cable elements is provided as an exemplification of possible embodiments of the present invention. The scope of the present invention is defined in the claims.

Description of the cable electrode elements:

The conductor:

Be based on Copper conductors or Copper alloys, flexible and stranded. The conductors may consist of strength members, as other metals, as steel or polymer yarns, based on aramide, polyester, PP or carbon.

The conductor cross-section area is typically between 1- and 10 mm ² , typically 1.5 and 2.5 mm ²

The polymer layer of the active section:

The insulation thickness of the active cable electrode is typically between 1- and 10 mm, in another aspect typically from 3 to 6 mm.

The insulation may consist of one or more layers of the same polymer compounds/materials or in combination with different compounds, with different individual properties. The active insulation material should preferably be based on so called "semi- conductive" polymer compounds, i.e. with a volume resistivity adapted to provide an electrical field and/or electric current efficient in deactivating the unwanted organisms.

A known method for measuring volume resistivity on a plaque of the polymer material is ASTM D991. Dependant of the conditions used to deactivate the lice in one aspect of the present invention the active polymer layer comprising a conductive filler has a volume resistivity, but not restricted to, less than 120 Ohm cm at 23 °C measured according to ASTM D991. In another aspect of the present invention the active polymer layer comprising a conductive filler has a volume resistivity, but not restricted to, higher than 10000 Ohm cm at 23 °C measured according to ASTM D991.

ASTM D991 measures volume resistivity with current flowing in the axial direction, and tests have shown that this does not necessarily relate to the resistivity that limits the current flowing in the radial direction as is the case with the cable electrodes according to the present invention. Cable electrodes with different active polymer layer with similar volume resistivity measured according to ASTM D991 showed very different radial volume resistivity.

Another known method for measuring volume resistivity is IEC 60502: According to this method measurements are performed on insulated conductor samples at 23 °C. In one aspect of the present invention the volume resistivity of the active polymer layer is, but not restricted to, between 3 and 50 Ohm cm by conductor screen formula and typically between 3 and 10 Ohm cm. In another aspect of the present invention the volume resistivity of the active polymer layer is, but not restricted to, between 10- and 100 Ohm cm by insulation screen formula and typically between 5- and 50 Ohm cm. In yet another aspect the volume resistivity is, but not restricted to higher than 10000 Ohm cm.

To overcome the problems experienced with ASTM D991 a new test method for measuring values that are directly related to the radial conductivity. This test is referred to as the Nexans test. The preparations for this test is illustrated on figure 9 showing a longitudinal cross- section of a test cable.

The conductor 5 provided with the active polymer layer comprising a conductive filler 14 is prepared for testing by applying a layer of silver lacquer 8 in intervals along the circumference of the conductor, each layer is of equal width. The sample is conditioned at 23°C 50%RH for at least 24h.

Thereafter a voltage of 5V AC is applied between the end of the conductor (where insulation is removed) called point A and a second point on a layer of silver lacquer to be measured (called B, C, D etc.). The current in the circuit is measured and this value is used as a measurement of radial conductivity. For each sample statistical data based on -25 such measuring points are evaluated.

Trials in sea have shown that values from 4 to 120 mA measured this way results in too high power consumption due to low resistivity. Typical values on good samples will be in the area 0.05 to 2.0 mA, preferably 0.05 to 1mA when measuring this way. If higher power consumption is acceptable materials resulting in values between 0.05 to 5 mA could be used.

The polymer compounds shall be based on thermoplastic, polymer materials, with base from the following polymers: PE and its copolymers, TPE s, as for example polyurethane or polyester/ether-based, or different blends of such.

The active part of the cable elements shall have properties as described above, but not be limited to the given examples and shall normally be active in the water/sea.

The electrical insulating polymer in the end section:

The far/bottom end of the active part shall be sealed by an electrically insulating polymer, preferably by a water-tight polymer.

The insulating polymer of the connection section:

For connection to the electrical pulse generator grid the active cable section is connected to an insulated conductor above comprising polymer insulating insulation layer, or more, with a higher volume resistance than the polymer in the active section.

This insulation may consist of polymer compounds based on, as for example: polyvinylchloride (PVC), polyethylene (PE) and its copolymers, or thermoplastic elastomers (TPE ^' s). Figure 5 illustrates how the cable electrode according to the present invention can be utilized. A fish corral arrangement 10 comprises a corral bag 20 hanging from a floating buoyant circular structure comprising a path or gangway 1 1 for inspection and maintenance. A plurality of cable electrode elements 30 according to the present invention are installed as vertical poles surrounding the corral bag. In one embodiment the corral bag is electrically conductive or comprises conductive elements. A voltage of opposite polarity is supplied to the poles and the corral bag to create an electrical fence in the area between the outside of the corral bag and the poles. In another embodiment the corral bag is non-conductive and not electrically connected to the poles. Instead a voltage of opposite polarity is applied to adjacent poles resulting in an electric current between the adjacent poles. In a further embodiment the poles are wired to a generator in sections so that they can be switched on and of section wise and it is possible only to activate the section(s) on the upstream side of the corral. Thereby the organisms flowing with the water current will be inhibited/limited from entering the corral, while the power consume is reduced.

Figure 6 illustrates another use of cable electrodes according to the present invention. Here the connection section 42 of a number of cable electrodes are connected to a electrical pulse/voltage generator 50. The active section 43 of the cable electrodes are connected to the coarse mesh made up of the strings 22, 24 and 28 of a corral bag. The end sections 44 of the electrode cables are arranged at the bottom and according the electrodes are arranged as parallel generally vertical strings.

Figure 7 illustrates an embodiment where the connection end of a plurality of cable electrodes 142 are connected to a pulse/voltage generator 150. The generator 150 is arranged on top of a buoyancy member 1 10 to with a corral bag is secured. The active sections 143 of the cable electrodes are secured to the fine mesh of the corral bag as parallel generally vertical strings. The free end sections 144 are arranged at the bottom of the coral bag. The dimension of the cable electrodes is selected according to the intended embodiment and the foreseen distance between neighboring electrodes.

Figure 8 illustrates schematically an embodiment of the present invention wherein a plurality of the cable electrodes 230 forms a fence 260 along a number of fish farming unit 210. Further indicated on the figure is the polarity of the cable electrodes. Preferably the polarity changes to the opposite (from positive to negative or from negative to positive) between each adjacent cable electrode. Preferably the electricity is supplied in pulses.

In one embodiment of the present invention the distance between two adjacent cable electrodes in the fence is between 1-50 cm, preferably 5-25 cm, and more preferably 7-15 cm.