Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
  • H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
  • H01R4/58—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation characterised by the form or material of the contacting members
  • H01R4/66—Connections with the terrestrial mass, e.g. earth plate, earth pin

Definitions

• the present invention relates to the transmission of high voltage direct current and relates more specifically in one aspect to a process for said transmission underground and/or in water, and in another aspect, to an electrode to be used as one pole, for said transmission of high voltage direct current, whereby an insulated cable is used as the other pole and whereby the elec- t -jdes are intended to be arranged in a stationary manner in bore holes in the earth, or submerged in water.
• Electrodes for transmission of high voltage direct current in water where an insulated cable is used as one conductor and seawater is used as the return conductor between two electrodes, are known from the Swedish pate /t, published under number 460938. These electrodes are arranged in the form of mats which are spread on the sea bed and anchored there, whereby the total surface exposed to the seawater can reach several thousand square meters. Since the cost for cables is halved by using a system having one cable and using the sea water as the other conductor, enormous savings are made when installing the system for transmission of high voltage direct current over greater distances, such as across the Baltic Sea.
• the resistance may be varied by selecting different types of conductive material and taking advantage of variant cross sectional areas.
• the current is important as a parameter since it is included as a square term.
• one purpose with the present invention is to achieve a process for ground transmitted high voltage direct current which does not entail the risks which up to now have been associated with such transmission. Said purpose is achieved with the process according to claim 12, whereby a layer in the earth's crust having high conductivity is used as conductor and return conduction takes place via a cable.
• Another purpose of the present invention is to achieve an electrode to be used as an anode and/or cathode in said trans ⁇ mission of high voltage direct current. This is achieved by means of an electrode according to claim 1.
• FIG. 1 schematically illustrates an electrode according to the invention
• Figure 2 is a cross sectional view of the bottom part of an electrode module according to the invention.
• Figure 3 illustrates the spoke/star formed sheet metal elements
• Figure 4a illustrates an embodiment of the joint between two electromodules in detail
• Figure 4b illustrates a preferred embodiment of a joint
• Figure 5 illustrates the design of the coating and the barrier layer
• Figure 6 illustrates a cross sectional view through the ground with two bored holes in which electrodes are submerged, and one continuous cable running under- grour, and having a layer in the ground which con ⁇ ducts current, for example, salt-containing water.
• the process according to the invention is based on the use of a specially designed anode unit 1 for this purpose (in combination with a cathode) preferably with circular cross section and having a central current lead-in means 2, preferably of copper (Fig. 1).
• the inner part of the electrode 1 consists in one preferred embodiment of a metal element 3 arranged in spoke-form (cf. Figs. 3a-b), and arranged in conductive contact with the central current lead-in means 2 of copper.
• the plate element 3, preferably of titanium, is welded onto a titanium pipe or tube 15 in which the copper conductor 2 is inserted.
• These elements 3 are provided with an electrochemically active layer 4. Also other structures having large areas may be considered, the important thing being that one attains an enlarged active surface.
• the current lead-in means 2 and the sheet metal or plate elements 3 are covered, at least partially, by a protective casing 5, preferably having circular cross section, but even polygon or square cross sections are possible (cf. Fig. 2).
• the primary aim with the protective casing is to protect the spoke-formed sheet metal or plate elements 3, when the electrode is submereged in the bored hole.
• the surface of the casing is broken up by a large number of holes 6, either by perforating the material of the casing or also by using expanded metal for the casing.
• the holes 6 enable an electrolyte to circulate and prevent over-pressure due to build-up of gas.
• the perforated casing may also be provided with an active coating, but there are applications where it is preferred that the surface is uncoated.
• the electrode casing 5 is produced for this purpose in a suitable metal, such as, titanium, zirconium, niobium, tantalum or compositions thereof and they may, as already mentioned, for this purpose, be provided with a suitable electro-catalytic coating, whereby the casing 5 forms an active part of the anode.
• a suitable metal such as, titanium, zirconium, niobium, tantalum or compositions thereof and they may, as already mentioned, for this purpose, be provided with a suitable electro-catalytic coating, whereby the casing 5 forms an active part of the anode.
• Said coating may consist either of a mixed oxide, where normally one of the base metal oxides is mixed with a precious metal, preferably ruthenium, palladium, iridium or platinum. What is of importance, rather than the thickness, is the composition of the coating, which is calculated dependent upon the number of ampere-hours which the electrode is expected to be subjected to during its lifetime (30 - 40 years). In one especially preferred embodiment a coating which greatly supresses chlorine gas development has been selected.
• Coatings of the above mentioned types are known and it is within the field of competence of one skilled in the art to select a coating having the desired properties.
• a coating which supresses chlorine the main part of the discharged current on the anode leads to oxygen development.
• Dependent upon the the kind of electrolyte, in certain cases even a non-precious metal- containing coating may be selected, for example, one comprising tin oxides and/or manganese oxides.
• the electrode 1 illustrated in Fig. 2 is built up of modules 9 (cf. Fig. 6) and is screwed on or joined in another way to the mounting place in segments of about 3-10 meters.
• modules 9 cf. Fig. 6
• a joint is illustrated in Fig. 4a, and a preferred joint is illustrated in detail in Fig. 4b.
• the joint in the illustrated embodiment comprises a threaded unit 17.
• the titanium pipe 15, at the lower part of every module is provided with a socket 19 of titanium, welded 22, onto the pipe 15.
• a socket 19 to fit socket 23 is welded onto every module at its upper end.
• the socket 19 is of male type, and the socket 23 is of female type.
• the socket 19 is threaded on the outside and the socket 23 is threaded on the inside.
• the current from the central conductor 2 is transmitted via the intermediate piece 24 to the pipe 15, which in its turn carries the current to the electrode element 3.
• the contact between the conductor and the intermediate piece 24 is achieved by drawing the joint 17 to a sufficient torque.
• Fig. 4b illustrates an improved variant of the joint in Fig. 4a.
• the additional characteristics comprise of an O-ring seal 26. Furthermore the female piece 23 is provided with a key handle 27 to assist assembly. A shoulder 28 for a tool is also arranged to enable the module to be driven down into the bore hole in a dependable manner.
• holes 10 are bored in the earth's crust at end points of the length over which the current shall be transmitted (cf. Fig. 6).
• Hole 10 is bored to a depth where there are salt deposits and salt- containing water 11.
• An electrode is mo ited in such a bore hole at each end.
• An insulated cable 12 suitably is buried down in the ground to comprise one conductor, and the salty water 11 comprises the other conductor.
• an artificial electrolyte is then supplied via a feed cable 13 which runs parallel with the central conductor 2.
• a suitable electrolyte for this purpose is thus supplied, for example, sodium sulphate.
• the following reaction takes place in the bore shaft at electrode 1.
• the electrode 1 may be covered with a fitted diaphragm for this purpose having low permeability to the electrolyte, made of, for example, tightly woven teflon fibers, or of a sintered material such as Goretex (R) . Said diaphragm is added as a "bag” over the electrolyte 1 and functions by keeping the reaction solution in place.
• a diaphragm 14 may be advantageous since there is sodium chloride in the electrolyte which surrounds the electrode 1 when this functions as an anode, but when one wishes to completely avoid chlorine gas development.
• an artificial, mainly chloride-ion-free environment may be maintained at the anode 1, whereby the undesirable chlorine gas development may be avoided.
• a special gas collecting pipe which leads to a device above the ground and in which the chlorine gas is occluded by scrubbing in a simple scrubber by means of diluted sodium hydroxide (at full power only about 1-2 kg chlorine develops per hour) .
• an anodic construction and a corresponding cathodic construction is used.
• a corrosion resistant material usually stainless steel, nickel or nickel alloys are preferred.
• the cathode (not shown) which has the same construction as the anode, is not supplied with any electrochemi ⁇ cal active coating. In cases where low corrosion and a definite cathodic polarisation can be achieved, sometimes a soft iron for the construction material may be considered.
• the cathode must be provided with an extra lead-in 16 for inert gas, for example, nitrogen, and in this manner the build-up of explosive hydrogen gas may be avoided.
• the electrode according to the invention is reversible. This means, therefor, that it may be used both as an anode and a cathode. This may be achieved by, on the one hand, doubling the active surface or enlarging even more, by for example, doubling the number of spokes, whereby the current density decreases.
• it may comprise an electro- catalytic coating 4, which tolerates extended use both as anode and cathode. Said coating is the same as for anode production, but comprises an additional barrier layer 18 of non-stoichiomet- ric TiO x (cf. Fig 5). By applying the electrochemically active coating 4 over this barrier layer 18 of TiO r hybrid formation is prevented, especially at higher temperatures.
• Said barrier layer of non-stoichiometric titanium oxide may be applied .with the aid of an in situ oxidation, flame spraying, plasma spraying or in some other suitable manner.
• Said layer 18 comprises, thus, a support for the electrocatalytic coating 4.
• one doubles the electrode surface as mentioned, by increasing the number of spokes 3, and by usually preparing the outer casing surface 5 with an active coating, i.e. an electrochemical coating 4 of the same type as on the spokes.
• the lead-in 16 plays a very important part regarding the inert gas, since otherwise explosive mixtures of hydrogen gas, chlorine gas and oxygen can form.
• the reversible electrode is also provided with a lead-in means 13, as well as an optional lead-outs for electrolyte positioned at different heights in the bore hole 10.
• the inner copper conductor is strengthened by weaving in durable steel thread.
• the metal may be suitable to alloy the metal with suitable alloy-materials, to attain a greater mechanical strength.
• suitable alloy-materials for example, aluminium, vanadium, zirconium etc. , whereby an important increase of the yield point is achieved.
• a normal dimension of an anode is a diameter of 70 mm and a height of 75 to 150 m. Such an element may transport 400-600 A. However, obviously, the outer dimensions can vary, and the diameter may be increased up to at least 200 mm. Although even if greater dimensions are obviously possible, they would be so clumsy that for this reason they would be unsuitable. Likewise, one may obviously attain longer or shorter electrodes. Normally at least three electrodes of each kind should be used in their own bore hole for transmitting current, where two together can transmit ground current. By this means one is given the opportunity of carrying out maintenance work, reactivating the electrode etc. , without interrupting the power.
• the electrodes should be provided with a feed line for inert gas all the way down to the bottom of the electrode.
• a feed line for inert gas all the way down to the bottom of the electrode.
• branch pipes down the electrode to supply inert gas at certain points along the entire electrode. The purpose is to achieve the remixing which might be prevented due to " chlorine which develops and is dissolved in the elec ⁇ trolyte.

Landscapes

• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
• Geophysics And Detection Of Objects (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

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Family Applications (1)

Country Status (5)

Cited By (5)

Citations (4)

• 1993
  • 1993-06-23 SE SE9302182A patent/SE506257C2/sv not_active IP Right Cessation
• 1994
  • 1994-06-23 AU AU70903/94A patent/AU7090394A/en not_active Abandoned
  • 1994-06-23 WO PCT/SE1994/000635 patent/WO1995000984A1/en active Application Filing
  • 1994-11-22 EE EE9400156A patent/EE9400156A/xx unknown
• 1995
  • 1995-12-22 NO NO955277A patent/NO955277L/no not_active Application Discontinuation

Patent Citations (4)

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