Method for arranging electrodes in an electrolytic process and an electrolytic system

In the method and system, a number of electrolytic cells are arranged as a cell group, which cells are separated by a number of partition walls; in each cell, a number of anodes and cathodes are arranged in an alternating order, so that in each cell, next to each anode, there is arranged a cathode, and so that in each cell, each individual anode is fitted in the same anode line with the anode of the adjacent cell, and in each cell, each individual cathode is fitted in the same cathode line with the cathode of the adjacent cell, and each anode is galvanically connected to at least one cathode of the adjacent cell. The flowing direction of the current passing in the cell group is deviated in different directions in order to make the current flow mainly in the direction of the cell group.

FIELD OF THE INVENTION

The invention relates to a method for arranging electrodes in an electrolytic process. Further, the invention relates to an electrolytic system.

BACKGROUND OF THE INVENTION

The electrolytic reduction of metals (electrorefining or electrowinning) is carried out in several electrolytic cells, in which electrodes (anodes and cathodes) are loaded in an alternating order. Individual cells are arranged in cell groups by coupling the cells electrically in series by means of a separate contact system. This kind of contact system includes a busbar (so-called partition wall busbar), the task of which is to distribute the electric current evenly from the cathodes of the preceding cell to the anodes of the next adjacent cell.

From the field of electrolytic reduction of metals (electrorefining and electrowinning), there are known busbar systems representing two principal types.

The busbar system of the first main type is characterized by a uniform partition wall busbar. This kind of systems are widely used on the industrial scale in electrolytic plants. One application is known from a so-called Walker busbar system that is presented in the publication U.S. Pat. No. 687,800. There a number of electrolytic cells is arranged to form a cell group, where the cells are separated by a number of partition walls. In each cell, there are arranged in an alternating order a number of anodes and cathodes, so that in each cell, there is a cathode next to each anode. In addition, each individual anode in each cell is positioned in the same line—which in this specification is called the anode line—with the anode of the adjacent cell, and each individual cathode in each cell is positioned in the same line—which in this specification is called the cathode line—with the cathodes of the adjacent cell. A uniform busbar extending along the whole length of the cell is arranged on top of the partition wall between each of two adjacent cells in order to galvanically connect all of the anodes of the cell with all of the cathodes of the adjacent cell. In the publication EP 1095175 B1, the Walker system is developed further by adding equipotential bonding rails for the electrodes. The system is also known by the name “Outotec Double Contact Bus Bar System”. It can be used for alleviating the effect of contact errors between the busbar and the electrodes.

The present invention relates to segmented partition wall busbar systems according to the second main type mentioned above, and the Optibar system can be considered as representative of the nearest prior art with respect to the invention at hand.

FIG. 1illustrates a known Optibar system. A number of electrolytic cells1is arranged to form a cell group, where the cells are mutually separated by a number of partition walls3. In each cell, there are arranged, in an alternating order, a number of anodes A and cathodes C, so that in each cell, next to each anode A there is placed a cathode C, and further so that in each cell, each individual anode A is in the same anode line LAwith the anode of the adjacent cell, and that in each cell, each individual cathode C is in the same cathode line LCwith the cathode of the adjacent cell. The busbar4is arranged on top of the partition wall3arranged in between each adjacent cell. The busbar is formed of a row of conductor segments5that are separated galvanically from each other. Each conductor segment5is arranged to galvanically connect each anode A always with one cathode C of the adjacent cell. In each cell, the anode located in the anode line is galvanically connected by the conductor segment5in pairs (as can be seen inFIG. 1) to the cathode in the adjacent cell, located in the adjacent cathode line placed on the same side of the anode line. Thus the electric current proceeds directly from the cathode of the preceding cell to the anode of the following cell. Because each conductor segment in between different cells always proceeds in the same direction, inside the cell group electric current flows in parallel with the imaginary cell diameter (which is in the drawing illustrated by arrows drawn in between the anodes and cathodes; said arrows schematically illustrate the proceeding of current in the electrolyte in between the anode-cathode pairs).

Disturbances that are generally and typically detected in electrolysis are:contact error between electrode and busbarirregular electrode intervals (differences in distances between electrodes)short circuit between anode and cathodedisturbances caused by the electrolyte (for example additive treatment of copper electrolysis).

The basis for a well functioning electrolysis is that current distribution for individual electrodes in the electrolytic cell is as even as possible, from the beginning of the electrolytic cycle to the end. Now, particularly in the beginning of the electrolytic cycle, the effect of contact errors between the electrodes and the busbar must be minimized. As a consequence of contact errors, for instance the specific energy consumption in the electrolysis and the probability of short circuits is increased. The created short circuits in turn result in a decrease of current efficiency. Also the irregularity in the mass distribution of the cell cathodes is likewise increased. Irregular electrode intervals (distance differences) are mainly due to electrode rifling errors, deviations in electrode thicknesses, bending of electrodes and wrong position in suspension. As a consequence of an irregular electrode interval, the distribution of electrolyte resistance in the cell group is not even. Further, as a consequence of an irregular electrode interval, the probability of short circuits is increased, and the current efficiency is decreased. In case of a short circuit, current proceeds through the short circuit directly from the anode to the cathode. Naturally this results in that the current efficiency is decreased, and the quality of the metal precipitated on the surface of a short circuited cathode is weakened.

A wrong composition of the electrolyte can mean that both the chemical and physical qualities of the metal precipitated on the cathode surface are weakened. The weakening of the physical quality results in an increase of the number of short circuits, and in a decrease of the current efficiency. By means of the structure of the partition wall busbar, it is possible to restrict the effects of the drawbacks caused by the three first types of disturbances.

The advantage of the segmentation of the partition wall busbar in the Optibar style is that it cuts down the short circuit current. Owing to the use of a segmented busbar, the current efficiency in the cell group is good also in case of a short circuit. A good current efficiency is achieved because the segmentation of the busbar restricts the quantity of the electric current that is transferred to the short circuited electrodes.

However, a drawback of the Optibar system is that it causes a remarkable distortion in the distribution of the effective current in the cell group, wherefore the Optibar system is problematic in use. This remarkable phenomenon has not been identified in the above mentioned articles /1/-/3/on the Optibar system, because there the cathode streams are observed by a coarse resistor network analysis. Instead, the articles emphasize the evenness of the current distribution.

The distortion of the effective currents that takes place in the Optibar system is illustrated byFIG. 2obtained from the FEM simulation model.FIG. 2illustrates an electrolytic system that is meant for copper electrorefining.FIG. 2is a schematical illustration of a cell group with 7 cells, where each cell includes 60 electrode intervals, i.e. 31 anodes and 30 cathodes. By FEM model simulation, there is obtained an effective current distribution in a cell group in a so-called ideal i.e. undisturbed situation according to the drawing, without short circuits etc. Here the term ‘effective current’ refers to the current passing through the electrolyte and participating in the metal precipitation process. As was mentioned above, it would be advantageous that the effective current distribution were as even as possible, so that the obtained layer of metal precipitated on the cathodes is evenly thick, i.e. the mass distribution of the cathodes is as even as possible. In the example, the optimal effective current in all electrode intervals of the whole cell group would be for instance 325 A. However, in the Optibar system ofFIG. 2, the obtained current distribution range is large, extending from the value 0 A to the value of roughly 700 A, as can be seen from the vertical column on the right-hand side of the Figure. In the center of the cell group, the situation is still good, i.e. the effective current remains within an acceptable range, which inFIG. 2is represented by the cross-hatched area. On the other hand, problems are detected at the ends of the cells, owing to an effective current that is either too high or too low. From the Figure it can be seen that in the last electrode intervals in the top left-hand corner, and in the first electrode intervals of the bottom right-hand corner, effective current does not flow at all, i.e. the prevailing effective current is 0 A. Now metal is not precipitated on the cathode at all. A deficient layer of precipitated metal on the cathode surface in turn causes problems in the mechanical separation of metal from the permanent cathode. Further, fromFIG. 2it is seen that the effective current in the electrode intervals in the bottom left-hand corner and in the top right-hand corner approaches the top limit 700 A of current distribution. An excessive effective current causes a rapid precipitation of metal on the cathode surface, which can result in short circuits.

OBJECT OF THE INVENTION

The object of the invention is to eliminate the above mentioned drawbacks.

A particular object of the invention is to introduce an electrolytic system, particularly suited in electrorefining, that has all the advantages offered by a prior art system provided with a segmented busbar, and at the same time avoids the drawbacks of said prior art system, i.e. provides an even current distribution and good current efficiency in a cell group.

Further, an object of the invention is to introduce an electrolytic system, where an even cathode mass distribution, a low probability of short circuits and a low specific energy consumption are achieved. The object is to obtain an improved quality of precipitated metal, an increased production output and a decreased energy consumption.

SUMMARY OF THE INVENTION

According to the invention, the flow direction of the current proceeding in the cell group is in the method deviated in different directions in order to make the current flow mainly in the direction of the cell group. Here the term ‘the direction of the cell group’ refers to the horizontal direction that is perpendicular to the lengthwise direction of the cell.

According to the invention, the conductor segments of the busbars are in the system arranged so that one or several anodes in one or several anode lines in one or several cells of a cell group are connected to one or several cathodes of the adjacent cell, of which cathodes at least one is located in the adjacent cathode line placed on the first side of said one or several anode lines, and that one or several anodes in some other one or several cells of the cell group, in said one or several anode lines, is connected to one or several cathodes of the adjacent cell, of which cathodes at least one is located in the adjacent cathode line placed on the other side of said one or several anode lines.

An advantage of the invention is that the deviation in the current distribution caused by the busbar segmentation is corrected in one or several cell intervals in the opposite direction, so that the current, flow proceeds essentially directly in the direction of the cell group, and not diagonally as in the prior art.

In comparison with the current distribution provided in the prior art system, the current distribution in the cell group of the invention becomes more even, because the so-called “inversion” of the partition wall busbars effectively corrects the deviation in the current distribution, caused by the geometry of the contact system. An even current distribution results in an even cathode mass distribution, a lower probability of short circuits and a lower specific energy consumption. Also the quality of the metal precipitated on the cathode surface is improved. Owing to the use of a segmented busbar, the current efficiency in the cell group is good, also in case of a short circuit. A good current efficiency is a consequence of the fact that the busbar segmentation restricts the magnitude of the electric current passed on to short circuited electrodes.

In an embodiment of the method, one or several anodes located in one or several anode lines in one or several cells of a cell group are connected to one or several cathodes of the adjacent cell, of which cathodes at least one is in the adjacent cathode line located on the first side of said one or several anode lines, and one or several anodes, located in some other one or several cells in said one or several anode lines of the cell group, are connected to one or several cathodes of the adjacent cell, of which cathodes at least one is located in the adjacent cathode line placed on the other side of said one or several anode lines.

In an embodiment of the method, one or several anodes, placed in one or several anode lines in an alternating order in every, second cell, are connected to one or several cathodes of the adjacent cell, of which cathodes, at least one is located in the adjacent cathode line placed on the first side of said one or several anode lines, and respectively one or several anodes, placed in said one or several anode lines in an alternating order in every second cell, are connected to one or several cathodes of the adjacent cell, of which cathodes at least one is located in the adjacent cathode line placed on the other side of said one or several anode lines. In this embodiment, the deviation in the current distribution is corrected in every second cell interval.

In an embodiment of the method, the individual anodes in each cell are galvanically connected to the individual cathodes of the adjacent cell.

In an embodiment of the method, two or several anodes of each cell are galvanically connected to each other and to a corresponding number of cathodes of the adjacent cell.

In an embodiment of the method, at the end of the cell, two or several anodes are connected to one or several cathodes of the adjacent cell.

In an embodiment of the method, the anodes in each cell are galvanically interconnected in order to balance the potential. Owing to the use of potential balancing, the cell group includes only few anodes that are in a serious contact error.

In an embodiment of the method, the cathodes in each cell are galvanically interconnected in order to balance the potential. Owing to the use of potential balancing, the cell group includes only few cathodes that are in a serious contact error.

In an embodiment of the system, one or several anodes, located in one or several anode lines placed in an alternating order in every second cell, are connected to one or several cathodes of the adjacent cell, of which cathodes at least one is placed in the adjacent cathode line located on the first side of said one or several anode lines, and respectively one or several anodes placed in an alternating order in every second cell in said one or several anode lines, are connected to one or several cathodes of the adjacent cell, of which cathodes at least one is located in the adjacent cathode line on the other side of said one or several anode lines.

In an embodiment of the system, each individual anode in each cell is galvanically connected to an individual cathode of the adjacent cell.

In an embodiment of the system, two or several anodes in each cell are galvanically connected to each other and to a corresponding number of the cathodes of the adjacent cell.

In an embodiment of the system, at the end of the cell, two or several anodes are connected to one or several cathodes of the adjacent cell.

In an embodiment of the system, the busbars include a first busbar and a second busbar, which is an inverted mirror image of the first busbar with respect to a vertical plane extending in the direction of the cell group.

In an embodiment of the system, the first and second busbars are arranged in an alternating order, on top of every second partition wall.

In an embodiment of the system, the anodes in each cell are galvanically connected to each other by a first equipotential bonding rail. The first equipotential bonding rail can extend along the whole length of the cell, to connect all anodes in the cell to each other. The first equipotential bonding rail can also extend to only part of the cell length, so that it connects several anodes, but not all of them. Such lengths of equipotential bonding rail can be located at the cell ends, and also in between the cell ends, somewhere in the middle region.

In an embodiment of the system, the cathodes in each cell are galvanically connected to each other by a second equipotential bonding rail. The second equipotential bonding rail can extend along the whole length of the cell, to connect all cathodes in the cell to each other. The second equipotential bonding rail can also extend to only a part of the cell length, so that it connects several cathodes, but not all of them. Such lengths of equipotential bonding rail can be placed at the cell ends, and also in between the cell ends, somewhere in the middle region.

The method and system are particularly feasible in the electrorefining process of metals.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3shows a schematical top-view of part of the electrolytic system according to the invention. There is seen a group of adjacent electrolytic cells1,2, each two of said adjacent cells1and2being separated by a partition wall3. In each cell, there is arranged, in an alternating order, a number of anodes A and cathodes C. In each cell, next to each anode A, there is always a cathode C and vice versa. Each individual anode A of each cell is in the same anode line LAwith the anode of the adjacent cell. Respectively, each individual cathode C of each cell is in the same cathode line LCwith the cathode of the adjacent cell. On top of each partition wall3between the adjacent two cells1,2, there is arranged a busbar4′,4″, formed of a row of conductor segments5,6, which segments are galvanically separated in the busbar. Each conductor segment5,6galvanically connects the anode A with at least one cathode C of the adjacent cell.

In the embodiment ofFIG. 3, the conductor segments5,6of the busbars4′,4″ are arranged so that one anode A located in one or several anode lines LA, in an alternating order in every second cell1, is connected to one cathode C of the adjacent cell2, said cathode being located in the adjacent cathode line LCon the first side of the anode line LA, inFIG. 3on the left-hand side. Respectively, the anode A placed in said same anode line LA, in an alternating order in every second cell2, is connected to one cathode C of the adjacent cell1, which is located in the adjacent cathode line LCon the other side of the anode line LA, i.e. on the right-hand side in the drawing. The busbars4′,4″ comprise, a first busbar4′ and a second busbar4″. The second busbar4″ is, with respect to a vertical plane that is drawn in the direction of the cell group, an inverted mirror image of the first busbar4′. The first and second busbars are arranged in an alternating order on top of every second partition wall3.

FIG. 4illustrates the system according toFIG. 3, provided with equipotential bonding rails7and8, which are here represented only schematically. The cross-hatched rails7interconnect the anodes A, and the white rails8interconnect the cathodes. In practice, the equipotential bonding rails7and8can be integrated in the partition wall busbar4′ and4″, for example in the same way as is described in the publication EP 1095175 B1. The anodes A placed in each cell1,2are galvanically interconnected by a first equipotential bonding rail7. Likewise, the cathodes C placed in each cell1,2are galvanically interconnected by a second equipotential bonding rail8.

FIG. 5illustrates an embodiment of the system including a group of adjacent electrolytic cells1,2, where each two of said adjacent cells1and2are mutually separated by a partition wall3. In each cell, there is arranged, in an alternating order, number of anodes A and cathodes C. In each cell, next to each anode A, there is always a cathode C, and vice versa. Each individual anode A in each cell is in the same anode line LAwith the anode of the adjacent cell. Respectively, each individual cathode C in each cell is in the same cathode line LCwith the cathode of the adjacent cell. On top of each partition wall3of the adjacent two cells1,2, there is arranged a busbar4′,4″, formed of a row of conductor segments5,6, which segments are galvanically separated in the busbar. Each conductor segment5,6galvanically connects the anode A with at least one cathode C of the adjacent cell.

FromFIG. 5it is apparent that in each busbar4′,4″, the conductor segments5,6are arranged so that two anodes A located in two neighboring anode lines LA, in an alternating order in every second cell1, are connected to two cathodes C of the adjacent cell2, one cathode of which is placed in the adjacent cathode line LClocated on the first side of each anode line LA, i.e. on the left-hand side in the drawing. Respectively, two anodes A located in said anode lines LA, in an alternating order every second cell2, are connected to the two cathodes C of the adjacent cell1, of which cathodes C one is located in the adjacent cathode line LCplaced on the other side of each anode line LA, i.e. on the right-hand side in the drawing. The busbars4′,4″ comprise a first busbar4′ and a second busbar4″. The second busbar4″ is, with respect to the vertical plane drawn in the direction of the cell group, an inverted mirror image of the first busbar4′. The first and second busbars are arranged in an alternating order on top of every second partition wall3.

FIG. 6illustrates yet another embodiment of the system, with a group of adjacent electrolytic cells1,2, each of said two adjacent cells1and2being separated by a partition wall3. In each cell, there is arranged, in an alternating order, a number of anodes A and cathodes C. In each cell, next to each anode A, there is always a cathode C, and vice versa. Each individual anode A in each cell is in the same anode line LAwith the anode of the adjacent cell. Respectively, each individual cathode C in each cell is in the same cathode line LCwith the cathode of the adjacent cell. On top of the partition wall3provided in between two adjacent cells1,2, there is arranged a busbar4′,4″, formed of a row of conductor segments5,6, said segments being galvanically separated in the busbar. Each conductor segment5,6galvanically connects the anode A with at least one cathode C of the adjacent cell.

InFIG. 6, it can be seen that in each busbar4′,4″, the conductor segments5,6are arranged so that three anodes A placed in three neighboring anode lines LA, in an alternating order in every second cell1, are connected to three cathodes C of the adjacent cell2, of which cathodes one is located in the adjacent cathode line LCon the first side of all three anode lines LA, i.e. on the left-hand side in the drawing. Respectively, three anodes A placed in said anode lines LA, located in an alternating order in every second cell2, are connected to the three cathodes C of the adjacent cell1, of which cathodes C one is located in the adjacent cathode line LCon the other side of all three anode lines LA. i.e. on the right-hand side in the drawing. The busbars4′,4″ comprise a first busbar4′ and a second busbar4″. The second busbar4″ is, in relation to a vertical plane drawn in the direction of the cell group, an inverted mirror image of the first busbar4′. The first and second busbars are arranged in an alternating order on top of every second partition wall3.

FIG. 7illustrates an embodiment of the electrolytic system ofFIG. 3, where at each end of each cell, five neighboring anodes A are interconnected by a length9′ of a first equipotential bonding rail, and four neighboring cathodes C are interconnected by another length9″ of the first equipotential bonding rail. Also in this embodiment the second busbar4″ is, in relation to a vertical plane drawn in the direction of the cell group, an inverted mirror image of the first busbar4′. The first and second busbars are arranged in an alternating order on top of every second partition wall3.

FIG. 8illustrates an embodiment of an electrolytic system that deviates from the embodiments ofFIGS. 3-7in that here the busbar is not inverted in every second busbar located in the cell interval between two adjacent cells, but the embodiment ofFIG. 8includes several adjacent cell intervals with a similar segmented busbar5, and after the described succession of similar busbars5, there is arranged an inverted busbar6, by, which the current flow is deviated in the other direction (in the drawing to the right), and in the part of the cell group illustrated in this example, there is provided one such inverted busbar. When necessary, they can also be arranged in several successive cell intervals.

FIG. 9illustrates yet another embodiment, where the busbars4′,4″ are, in relation to themselves, inverted with reference to the vertical plane drawn in the direction of the cell group, i.e. in each busbar, the direction of the conductor segments changes on the center level of the cell interval.

FIG. 10illustrates an effective current distribution, simulated by FEM modeling, for an electrolytic system that is modified from the Optibar system by a segmented busbar inversion according toFIG. 3. In addition, the cell ends in each cell are, according toFIG. 7, provided with lengths of equipotential bonding rail, where one length of the equipotential bonding rail interconnects five anodes, and the other length of equipotential bonding rail interconnects four cathodes. FromFIG. 10it is apparent that the effective current distribution throughout the whole cell group is fairly even. The deviation in the current distribution that was typical of the Optibar system illustrated inFIG. 2does not occur anymore. The effective current distribution scale is roughly from 290 A to 360 A, as is indicated by the horizontal column on, the right-hand side of the distribution diagram. In the majority of the electrode intervals, the effective current remains within a good range. The maximum current, of the order roughly 360 A, occurs in the first electrode interval of every second cell and in the last electrode interval of every second cell, is remarkably lower and better than in the prior art case ofFIG. 2, where the maximum current was over 700 A, and it occurred in several electrode intervals.

FIG. 11illustrates the current distribution for a system that is obtained from the system ofFIG. 3by adding a modified current segment that at the end of the cell connects several anodes to several cathodes of the adjacent cell. FromFIG. 11it is can be seen that the current distribution still remains fairly good. Zero currents do not occur at the cell ends. The scale of the effective current distribution is now roughly from 200 A to 450 A, as is indicated in the horizontal column on the right-hand side of the distribution diagram. In the majority of the electrode intervals, the effective current remains within a good range. Likewise, the maximum current that can occur at the other end of the cells remains within a perfectly acceptable range and does not make the precipitate grow too rapidly on the cathode surface. In addition, there can be used equipotential bonding rails in order to reduce the effect of contact errors.

FIG. 12illustrates the current efficiency as a function of the standard deviation of effective currents in cell groups provided with different partition wall contact systems.

The term ‘current efficiency’ here refers to the share of the current supplied in the electrolytic cell that is utilized as a metal precipitating effective current in the electrolysis. The object is to minimize the current efficiency loss. In an optimal situation, the current efficiency is 100%, i.e. the current efficiency loss is 0%, but in practice the short circuits and earth leakages occurring in the system result in that the current efficiency loss is bigger than zero. In an optimal situation, the divergence in the effective current distribution is as small as possible. Thus the target point is nearest to the bottom left-hand side corner in the coordinates ofFIG. 12.

The points occurring inFIG. 12, marked by the symbols □ and +, represent sample averages of the standard deviation of the effective current and the current efficiency loss in a case with power loss. In each cell, the system includes 30 cathodes and 31 anodes, and a cell group includes seven cells.

The symbol □ illustrates a system that is provided with previously known uniform partition wall busbars (so-called Walker system), with a corresponding sample average point a), where the sample average of the current efficiency loss is nearly 8%, and the sample average of the standard deviation of the effective current is roughly 55 A.

The symbol + illustrates a system formed according to the invention, provided with inverted and segmented busbars.The sample average points b)-g) illustrate systems provided with busbars divided into two b), three c) five d), six e), ten f) and fifteen g) parts, said busbars being in every second cell interval inverted according to the invention. It is pointed out that as the number of current segments increases, the current efficiency loss is decreased, and the standard deviation of effective currents increases. From the drawing it can be generally seen that by means of a system according to the invention b)-g), the current efficiency loss is throughout smaller than with a uniform busbar a).The sample average point h) illustrates a system where in each cell the anodes and cathodes have equipotential bonding rails (corresponding to the system ofFIG. 4). Now the standard deviation of effective currents is relatively small, roughly 53 A. The current efficiency loss is below 7.5%.The sample average point i) illustrates a fully segmented system where in each cell, only the anodes have equipotential bonding rails. The current efficiency loss is roughly 6.5%, and the standard deviation of effective currents is roughly 54 A.The sample average point j) illustrates a fully segmented system where in each cell, only cathodes have equipotential bonding rails. Now the current efficiency loss is roughly 5.5%, and the standard deviation of effective currents is roughly 54 A.The sample average point k) illustrates a fully segmented system where, according toFIG. 7, the equipotential bonding rails at both ends of the cell connect 5 anodes and 4 cathodes. Now the current efficiency loss is roughly 4%, and the standard deviation of effective currents is roughly 58 A. By means of this structure, there is achieved an even current distribution in an undisturbed situation, and a good performance in a power-loss situation.

All embodiments b)-k) according to the invention are so-called Pareto optimal. Points h)-k) prove that it is profitable to fully segment (and invert) the partition wall busbar (as inFIG. 3), and when necessary, equipotential bonding rails can be used, and the situation is never worse than in the case of point a).

By means of the prior art Optibar system, the standard deviation of effective currents would be of the order roughly 100 A, and would therefore not fit in the graph ofFIG. 12, because the standard deviation of effective currents would be so large.

The invention is not restricted to the above described embodiments only, but many modifications are possible without departing from the scope of the inventive idea defined in the appended claims.