US3903382A

US3903382A - Sub-station switch

Info

Publication number: US3903382A
Application number: US468572A
Authority: US
Inventors: Erich Silbermann
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1973-05-09
Filing date: 1974-05-09
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02
Also published as: DE2323386A1; FR2229130A1; GB1466451A; DE2323386C3; LU70011A1; DK143822C; NL7406245A; DE2323386B2; JPS5015078A; BE814584A; IT1012142B; FR2229130B1; DK143822B

Abstract

A switch for installation at a power distribution sub-station fed by a radial sub-transmission system in which, for each of the three phases supplied, a flat three-arm contact piece is arranged for rotation on a shaft with fixed contacts arranged in stationary relationship on the circumference of a ring around the contact piece. Five contact positions are uniformly distributed over the circumference of the ring with each two adjacent contact arms of the contact piece subtending an angle of 72* with fixed contacts installed at only four positions. The fixed contacts of the outgoing branch and of the radial subtransmission inputs include aligned jacks so that they can be separately grounded using a grounding rod. All switch positions customary and necessary for sub-stations of this nature can be obtained by rotating the shaft on which the contact pieces are mounted.

Description

United States Patent Silbermann Se t. 2 1975 SUB-STATION SWITCH [75] Inventor: Erich Silbermann, Bubenreuth, Primary Emmmer jjlmes Scott Germany Altar/1e Agent, or FlrmKenyon & Kenyon Re1lly Carr & Chapin [73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany 57 ABSTRACT [22] Filed: May 9, 1974 A switch for installation at a power distribution substation fed by a radial sub-transmission system in [21] Appl 468572 which, for each of the three phases supplied, a flat three-arm contact piece is arranged for rotation on a [30] Foreign Application Priority Data shaft with fixed contacts arranged in stationary rela- May 9 1973 Germany 2323386 tiohship the circumference of a ring around the contact piece. Five contact positions are uniformly 52 us. c1 200/11 TC; 323/62 distributed over the eheumterehee of the rhtg with 51 1m. 01 HOlh 21/00; HOlh 1 /56 eeeh twe ediaeeht eehteet arms of the eehteet Pieee 58 Field of Search 200/1 R, 11 R 11 TC, 17 suhtehdhtg an angle of with fixed eehteets 200 8 5] R 5 l '02 5 104 50 C, stalled at only four positions. The fixed contacts of the 323/435 62 outgoing branch and of the radial subtransmission in puts include aligned jacks so that they can be sepa- [56] References Cited rately grounded using a grounding rod. All switch positions customary and necessary for sub-stations of this UNITED STATES PATENTS nature can be obtained by rotating the shaft on which 1,366,057 1/1921 Calverley et al 323/62 x the Contact pieces are moumgd 1,752,944 4/1930 E1tzen 323/62 X 2,134,560 10/1938 Kerr 323/62 22 Claims, 8 Drawing Figures PATENT ED EP 2197s SHEET 2 BF 3 PATENTEDSEP 21915 3.903 382 SHEET 3 [IF 3 FIG. l

SUB-STATION SWITCH BACKGROUND OF THE INVENTION This invention relates to power distribution in general, and more particularly to an improved sub-station switch for use with a radial sub-transmission system.

Radial sub-transmission systems are systems used for transmitting an intermediate voltage between, for example, a power sub-station and a distribution substation. For discussion of such systems, see Standard Handbook for Electrical Engineers," edited by Donald G. Fink and John M. Carroll, th Edition, McGraw- Hill, 1968, section 16-43 to l650. When using such radial sub-transmission circuits, the load circuits are customarily provided with separate load disconnect switches and fuses. The energy from the power substation is supplied over one of the two lines through two disconnect switches which are connected into the circuit parallel to each other and which are often equipped with additional interlocking grounding switches. Various arrangements have been developed for use in such applications. German design Pat. No. 6,933,374 shows a multi-pole load disconnect for use in sub-stations in which a contact piece with three arms is arranged rotatably about a shaft with fixed contacts arranged in stationary relationship on the circumference of a ring around this contact piece. However, not all the switch positions generally provided and necessary for a substation can be obtained in this arrangement without removal of the switch. Thus, the normally used position in which none of the points to be connected is connected with another point, i.e., where both the radial sub-transmission circuits and the outgoing load circuit are all opened is not possible with this switch. This position with all circuits opened is required for various maintenance operations.

Thus, it can be seen that there is a need for an improved switch of this nature in which all the switch positions customarily available and necessary for substations can be provided simply by turning a shaft. In such a switch, the space required and the amount of hardware should be reduced to a minimum. Furthermore, the combination of the switch with the substation transformer, with the two elements as close as possible is desirable.

SUMMARY OF THE INVENTION This problem is solved in the switch of the present invention by providing, for each phase, more than four fixed contact positions distributed at equal angular increments around the circumference of a ring. Contacts are installed preferably at four of the contact positions. In the preferred embodiment, five total positions are used and the fifth position left open. A three arm contact piece is mounted for rotation about an axis passing through the center of the ring on which the contacts are mounted. The angular spacing of the arms is the same as that of the contacts so that for any position, the three pronged contact piece will be coupling three of the fixed contact positions. In the disclosed embodiment, two of the fixed contacts are coupled together and coupled to the outgoing load branch. On one side of these two contacts coupled together is a contact position coupled to no line. The remaining two fixed contacts are coupled to the incoming lines of the radial sub-transmission circuit. As will be more fully described below, this arrangement makes possible any desired interconnection. That is, it is possible to couple both radial lines to the outgoing line, to couple the radial lines together, to couple the outgoing line to one or the other radial lines and finally, to isolate the outgoing line and both radial lines. Also included according to the present invention are means for grounding all phases of the outgoing line and the two radial lines. This is done by means of a grounding rod with an interlocking device provided on the switch which rotates with the three-armed contact piece and insures that grounding can only be accomplished when the various lines are properly isolated.

In the disclosed embodiment, a ring with five contact positions, four of which contain active contacts and are equally spaced about the ring are provided for each phase, with separate three arm contact pieces arranged on a common shaft for rotation therewith to make the necessary contact for each phase. In the preferred embodiment, the contacts associated with each of the lines, i.e., the radial lines and the outgoing lines, for all phases are arranged one behind another along an axis parallel to the axis of rotation. The rings containing the contacts are contained within planes perpendicular to the axis of rotation. This permits simple switching of all three phases at one time. Furthermore, a simple and clearly understandable switch design is obtained which at the same time allows simple grounding through the use of grounding rods.

In the disclosed embodiment, each of the fixed contacts have a contact surface for establishing contact with the three armed contact piece and furthermore each have ajack or bushing which is located on an axis parallel to the axis of rotation passing through the corresponding contacts for all phases. Furthermore, there is provided a grounding member in the form ofa planer member similarly havingjacks aligned with the contact jacks. This permits inserting a grounding rod through the grounding plane jack and through thejacks on each associated contact for a given line, i.e., a radial line or the outgoing line. In addition, to prevent grounding of a line carrying a voltage, interlocking means is installed at the face of the ground plane mounted for rotation with the shaft on which the three-armed switching pieces are mounted. This interlocking means is in the form of a disk having appropriate holes or cutouts which will permit insertion of the grounding rod only when the switch is in a position indicating that the line to be grounded does not have a voltage thereon supplied by one of the other lines. In the disclosed interlocking device, the axis of the jacks associated with the radial line contacts intersect the disk at two points on the circumference of a first circle and the axis of the jacks associated with the outgoing branch intersect the disk at a point on the circumference of a second circle of a different diameter. This design permits a particularly simple and effective manner of grounding with the interlock providing for safe operation. Furthermore, this type of interlocking device is of extremely simple design; using a common grounding plate and a disk with guide holes. In the disclosed embodiment, the jacks are designed as fixed contacts and the grounding rod is made in an elastic manner so that it maintains good contact with the jacks when inserted. This results in considerable cost reduction since simple drilled holes may be used forjacks with only the grounding bar being of a complex construction. Since this is only a single piece as opposed to a plurality ofjacks contained within the switch, considerable simplification occurs.

The switch of the present invention will preferably be placed in a tank filled with insulating liquid or compressed gas. Particularly advantageous is the installation of the switch of the present invention in a transformer vessel also containing a sub-station transformer. The placement of the sub-station switch in this manner results in a substantial reduction of the dimensions of the entire switch structure. If it is further possible to build a switch into the transformer vessel of a transformer existing at a branch point, additional savings result due to the elimination of the cost of couplings, insulation pieces and connecting cables. It should also be noted that an expansion tank for a transformer vessel is also particularly advantageous as a vessel for containing the switch of the present invention.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective, exploded view of the switch of the present invention, partially in schematic form.

FIGS. 2a through 2e illustrate the five possible switch positions of the switch of FIG. 1.

FIG. 3 is a schematic perspective view of a grounding rod for use in the switch of the present invention.

FIG. 4 is a perspective view illustrating the switch of the present invention installed in a container filled with insulating liquid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 illustrates in a perspective, exploded view, the switch of the present invention. For each of the phases designated R, S and T, a planar member 5 is disposed with all the planer members 5 essentially parallel to each other. Each of the planar members 5 has an annular cutout on the inside to form a ring 51 on which are mounted a plurality of fixed contacts 2. With reference specifically to the phase R, which can be identified by the associated designations of the first radial line R second radial line R and outgoing line A it will be seen that there are established five contact positions designated respectively 24, 25, 26, 27 and 28. At each of the contact positions except position 26, a fixed contact having an inner contact surface 21 between two prongs of the contact is installed on the inside of the ring 51. As illustrated, the contact 28 is electrically connected to the radial line R the contact 27 to the radial line R and the

contacts

24 and 25 are coupled together and coupled to the outgoing line designated A Jacks in the form of holes or bushings or the like designated 22 are formed in the

contacts

28, 27 and 22. As will be more fully described below, these are used for grounding purposes.

Associated with each of the planer members 5 having the contacts 2 installed thereon, is a three armed contact piece 1 having

arms

15, 16, and 17. The three contact arms are mounted on a common shaft 11 for rotation therewith. Shaft 11 will be mounted in conventional fashion for rotation about an axis 12. The contact positions as noted above are equally spaced so that the angle between each two contact positions is 72. Similarly, the angular subtense of two adjacent arms on the contact piece 1 is also 72. It is evident that the contacts associated with the first radial line, i.e., the contacts of R S and T, are all aligned and that their associated jacks 22 all lie on a common axis. Similarly,

the jacks on the contacts associated with the second radial line designated by the three phases R S and T lie on a common axis. The same is true of the jacks 22 associated with the contacts 24 for the outgoing line. Placed in front of the three planer members 5, with the shaft 11 passing through a hole 42 therein, is a ground plate 4 which will be connected to ground in conventional fashion. Plate 4 is provided with three jacks or holes 41 which are aligned with the respective axes passing through the aligned holes or jacks 22 in the contacts mounted on the planes 5. Thus, it can be seen that a rod passing through the plate 4 along the axis 23 for example, would intersect the hole 41 and the holes 22 associated with the outgoing line. In this manner, these holes which act as jacks can all be coupled together and grounded to the ground plate 4, thus completely grounding all three phases of the outgoing line. However, it is only desired that this be possible if a voltage is not present on that line. To provide an interlocking arrangement in order that active contacts are not grounded, the disk 3 of the present invention is provided. Disk 3 is rigidly mounted to the shaft 11 for rotation therewith. It contains a hole 31 located on the circumference of a first circle designated 36. This hole upon proper rotation of the disk 3 will align with the hole 41 associated with the outgoing line, i.e., the hole through which axis 23 passes. Additionally, a cut-out 32 is provided. Cut out 23 lies on a second circumference of different size following that circumference for an angle of approximately 72. The lower end of the slot 32 is displaced 72 from the radial passing through the hole 31. At the upper end the slot 32 extends radially for a distance such that the end thereof is equivalent to a hole along the circumference on which hole 31 lies. The inner circle 35 is such that when properly rotated, this slot through the disk will line up with the holes 41 associated with the first and second radial lines. Consider the position in which the switch now is as shown on the figure. This position is also illustrated by FIG. 2b. In this position, the first and second radial lines are connected together through the

arms

15 and 16 at each phase. That is to say, the

arms

15 and 16 are engaging the contact surfaces 21 in their

respective contacts

27 and 28. As clearly illustrated by FIG. 1, each of the arms is between two extending portions of the respective contact. The outgoing line however, is not coupled to any of the radial lines and thus, is free of voltage. Therefor, it is permissible that this line be grounded. As can be seen, a grounding rod, such as the grounding rod shown on FIG. 3 and which will be described in more detail below, can be inserted through the slot 32, the hole or jack 41 and the jacks 22 associated with the outgoing line to couple the ground plate 4 and the contacts 24 together, thereby grounding the outgoing line.

However, the first and second radial lines do have voltages thereon and grounding is not permissible. As is evident from FIG. 1, their corresponding jacks 22 are not aligned with either the slot 32 or hole 31. Insertion of grounding rod 6 along the

axes

33, 34 will thus result in the rods only abutting against the plate 4 and going no further. Thus, only the outgoing line which is free of voltage can be grounded. A 72 clockwise rotation of the shaft 11 will result in the arm 15 making contact with contact 27 and coupling the voltage from the second radial line to the outgoing line via contact 25 and arm 17. This is shown on FIG. 2a. In this position, with these two lines connected together, it is assumed that they have a voltage thereon. But in this position, the first radial line is made available for grounding and a grounding rod may be inserted along an axis such as axis 33 through the slot 32 and the appropriate holes 41 and jacks 22 to ground all phases of the first radial line. In the position shown on FIG. 20, the

arms

15, 16 and 17 are connected together with the two radial lines and the outgoing line. In this position, no grounding should be possible. Reference to FIG. 1 will indicate that if the disk 3 is rotated 72 counter-clockwise from the position shown to the position of FIG. 2c, neither its hole 31 nor its slot 32 will be aligned with any of the holes 41 and insertion of a grounding rod post plate 4 is not possible. The position shown on FIG. 2d is one in which the first radial line is connected to the outgoing line. In this position, the second radial line is open and a grounding rod should be able to be inserted through the contact associated therewith. This corresponds to two successive counter-clockwise 72 rotations of the disk 3. It is evident from examination thereof that two such rotations will align the hole 31 with the hole 41 on the right hand side of the ground plate 4 permitting a grounding rod to be inserted therethrough and through the associated jacks 22 for the three phases of the radial line R The final position is that shown by FIG. 2e. In this position, both lines R, and R are disconnected from the outgoing line. With the disk 3 rotated along with the shaft 11 to the position shown on FIG. 22, the hole 31 will be aligned with the axis 23 so that a grounding rod may be inserted therethrough to ground all three phases of the outgoing line. The slot 32 will have one end of its circular portion which lies along the circle 35 aligned with the upper hole 41 and the outer end aligned with the hole 41 to the right thereby permitting grounding rods to be inserted therethrough to ground all three phases of the first and second radial lines. Thus, in this position each of the lines, i.e., the first and second radial lines and the outgoing line designated A, are isolated from each other and can be individually grounded to the ground plate 4. For operation of the switch, the shaft 11 will be rotated for example, by a switch lever from one switch position to the other, each rotation being a rotation of 72. Preferably, detents will be provided at the individual contact positions. Furthermore, the switch lever may be equipped with a built-in rapid-switching device of a well known type since all switching operations are achieved simply by turning the shaft. With the switch of the present invention, it is easy to provide automatic interrupt action with the capability for storing all switch positions with the outgoing branch connected. In the event of a short-circuit of any phase of the outgoing branch, all three phases of the branch circuit are switched off even if only one or two of the fuses in an individual phase opens. Furthermore, with the switch design of the present invention it is possible to use only a single rapid switching lever for normal switching along with the automatic rapid-interrupt operation. For maintenance purposes or for single switching operations, the rapid switching lever which is normally used as the automatic disconnect may then be used.

FIG. 3 illustrates a schematic perspective view of a grounding rod which may be used with the switch of FIG. 1. With the switch in any position except that shown on FIG. 26, alinment of openings in the disk 3 ground plate 4 and corresponding grounding jacks will be present along a grounding axis. A grounding rod is then inserted through the disk 3, through the grounding plate and then through the grounding jacks associated with the individual phases. As shown, the grounding rod includes a shaft or spiked portion 65, a protective shield 63 and a handle 64. An axis 66 is shown passing through the grounding rod. For the switched position shown on FIG. 1, the outgoing branch line can be grounded by inserting the grounding rod 6 along the axis 23. Upon such insertion, the

axis

23 and 66 will be coincident. The jacks 22 and 41 can be made as bendable or elastic contacts so that good contact at the circumference of'a solid grounding rod 6 will be obtained. However, design is much simplified if the jacks 22 and 41 are simply fixed jacks or holes through the respective contacts or grounding plate. In that case, in order to equalize the position tolerances of the jacks and to insure good Contact, the grounding rod 66 should be constructed so that it has spring properties transverse to its longitudinal axis 66 and should be additionally elastic in its cross section in order to maintain firm contact with the jacks.

FIG. 4 illustrates the switch of FIG. 1 installed in a container filled with insulating liquid. As illustrated, the whole switch assembly of FIG. 1 is mounted vertically within a container 75. The disc 3 forms the top of the container. The planar members 5 are shown in dotted lines to show the arrangement more clearly. The assembly can be press fitted within the container or attached using an epoxy or the like. As illustrated by the dotted line 73, the container is filled with an insulating liquid. This insulating liquid will thus cover all the switch contacts. Also illustrated is a handle 70 attached to the shaft 11 of the switch to permit rotating between the various switch positions. The incoming and outgoing line for each of the phases are illustrated being connected to ajunction box 77 in conventional fashion. As noted above, the tank may also be filled with a compressed gas if proper measures are taken for making the container gas-tight. Furthermore, rather than place the switch in a separate container, as shown by switch 79 it can be located within a transformer vessel 80 which also contains the substation transformer 81 and is filled with insulating liquid 83. Such will result in a reduction of the overall arrangement and additional savings. In addition, the switch may be located in the expansion tank for a transformer vessel.

Thus, an improved switch for use in a sub-station for a radial sub-transmission system has been shown. Although a specificembodiment has been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from the spirit of the invention which is intended to be limited solely by the appended claims.

What is claimed is:

l. A sub-station switch for selectively coupling the two lines of a sub-transmission radial circuit and an outgoing branch comprising:

a. a ring shaped member about the circumference of which are established a plurality of more than four equally spaced contact positions forming the corners of an equilateral polygon;

b. fixed contacts provided at at least four of said contact positions for coupling to the radial lines andoutgoing branch;

c. a flat contact piece having at least three arms mounted on a shaft supported for rotation about an axis passing through the center of said ring member, the angular subtense between the arms on said contact piece being equal to 360 divided by the number of contact positions, said contact piece being arranged to contact said fixed contacts when properly rotated;

d. means for individually grounding each of said contacts using a grounding rod; and

e. interlock means for the grounding rod.

2. A switch according to claim 1 wherein two adjacent fixed contacts are coupled to each other and to the outgoing branch line with the contact position next to said two coupled contacts unoccupied with the remaining two contacts coupled respectively to the first and second radial lines.

3. A switch according to claim 1 wherein the switch is installed in a tank filled with insulating liquid or insulating gas.

4. A switch according to claim 3 wherein said tank is a transformer vessel, in which a transformer is also installed.

5. A switch according to claim 1 wherein said switch is employed in a multi-phase system and wherein there is provided a ring having contacts positions and contacts thereon for each phase and wherein additional three arm contact pieces are provided on said shaft for each additional phase.

6. A switch according to claim 5 wherein the contacts on each ring are arranged so as to be aligned with corresponding contacts on the other rings along axes parallel to the axis of said shaft with contacts for the same line occupying the same relative position for each phase with said three arm contact pieces are similarly aligned, said rings with said fixed contacts and said contact pieces lying in planes essentially perpendicular to the axis of said shaft.

7. A switch according to claim 6 wherein each of said fixed contacts has a contact surface for establishing contact with said three arm contact piece and further includes ajack having an axis parallel to the axis of said shaft, with the axis of the jacks for all phases associated with a radial line or outgoing branch line lying on a common axis, said jacks comprising means for grounding their associated contacts with a grounding rod.

8. A switch according to claim 7 and further including grounded contact jacks aligned with the axis on which the jacks associated with said fixed contacts lie whereby a grounding rod may be inserted along an axis to ground said fixed contacts.

9. A switch according to claim 8 wherein said grounded jacks comprise holes in a grounded plate, said plate being essentially perpendicular to the axis of said shaft and further including a disk adjacent said plate, said disk rigidly attached to said shaft for rotation therewith, said disk containing a plurality of guide holes lying on circles of a diameter corresponding to the circles on which the holes in said common plate lie, said holes being arranged to permit insertion of a grounding rod when said shaft is rotated to a position where an associated group of contacts can be grounded without danger.

10. A switch according to claim 9 wherein the axes associated with the jacks of the two radial lines intersect a first circle on said disk and the axis of the outgoing branch intersects a second circle on said disk, said second circle being of different diameter than said first cicle.

11. A switch according to claim 1 wherein five fixed contact positions are distributed over the circumference of said ring member, the angle between each two contact positions being 72 and wherein the angular subtense between two arms on said three arm contact piece is an integral multiple of 72.

12. A switch according to claim 11 wherein two adjacent fixed contacts are coupled to each other and to the outgoing branch line with the contact position next to said two coupled contacts unoccupied with the remaining two contacts coupled respectively to the first and second radial lines.

13. A switch according to claim 12 wherein said switch is employed in a multi-phase system and wherein there is provided a ring having contacts positions and contacts thereon for each phase and wherein additional three arm contact pieces are provided on said shaft for each additional phase.

14. A switch according to claim 13 wherein the contacts on each ring are arranged so as to be aligned with corresponding contacts on the other rings along axes parallel to the axis of said shaft with contacts for the same line occupying the same relative position for each phase with said three arm contact pieces are similarly aligned, said rings with said fixed contacts and said contact pieces lying in planes essentially perpendicular to the axis of said shaft.

15. A switch according to claim 14 wherein each of said fixed contacts has a contact surface for establishing contact with said three arm contact piece and further includes a jack having an axis parallel to the axis of said shaft, with the axis of the jacks for all phases associated with a radial line or outgoing branch line lying on a common axis, said jacks comprising means for grounding their associated contacts with a grounding rod.

16. A switch according to claim 15 and further including grounded contactjacks aligned with the axis on which the jacks associated with said fixed contacts lie whereby a grounding rod may be inserted along an axis to ground said fixed contacts.

17. A switch according to claim 16 wherein said grounded contact jacks comprise holes in a grounded plate, said plate being essentially perpendicular to the axis of said shaft and further including a disk adjacent said plate, said disk rigidly attached to said shaft for rotation therewith, said disk containing a plurality of guide holes lying on circles of a diameter corresponding to the circles on which the holes in said common plate lie, said holes being arranged to permit insertion of a grounding rod when said shaft is rotated to a position where an associated group of contacts can be grounded without danger.

l8. A-switch according to claim 17 wherein the axes associated with the jacks of the two radial lines intersect a first circle on said disk and the axis of the outgoing branch intersects a second circle on said disk, said second circle being of different diameter than said first circle.

19. A switch according to claim 18 wherein at least two guide holes in said disk separated by one angular contact spacing are provided on said first cicle and two guide holes separated by two contact spacings on said second circle.

20. A switch according to claim 19 wherein the switch is installed in a tank filled with insulating liquid or insulating gas.

are fixed contacts, and where a grounding rod which is elastic transversely to its longitudinal axis and in its cross section is provided.

Claims

1. A sub-station switch for selectively coupling the two lines of a sub-transmission radial circuit and an outgoing branch comprising: a. a ring shaped member about the circumference of which are established a plurality of more than four equally spaced contact positions forming the corners of an equilateral polygon; b. fixed contacts provided at at least four of said contact positions for coupling to the radial lines and outgoing branch; c. a flat contact piece having at least three arms mounted on a shaft supported for rotation about an axis passing through the center of said ring member, the angular subtense between the arms on said contact piece being equal to 360* divided by the number of contact positions, said contact piece being arranged to contact said fixed contacts when properly rotated; d. means for individually grounding each of said contacts using a grounding rod; and e. interlock means for the grounding rod.

7. A switch according to claim 6 wherein each of said fixed contacts has a contact surface for establishing contact with said three arm contact piece and further includes a jack having an axis parallel to the axis of said shaft, with the axis of the jacks for all phases associated with a radial line or outgoing branch line lying on a common axis, said jacks comprising means for grounding their associated contacts with a grounding rod.

11. A switch according to claim 1 wherein five fixed contact positions are distributed over the circumference of said ring member, the angle between each two contact positions being 72* and wherein the angular subtense between two arms on said three arm contact piece is an integral multiple of 72*.

16. A swItch according to claim 15 and further including grounded contact jacks aligned with the axis on which the jacks associated with said fixed contacts lie whereby a grounding rod may be inserted along an axis to ground said fixed contacts.

18. A switch according to claim 17 wherein the axes associated with the jacks of the two radial lines intersect a first circle on said disk and the axis of the outgoing branch intersects a second circle on said disk, said second circle being of different diameter than said first circle.

21. A switch according to claim 20 wherein said tank is a transformer vessel, in which a transformer is also installed.

22. A switch according to claim 19 wherein the jacks on said contacts and said plate for the grounding rod are fixed contacts, and where a grounding rod which is elastic transversely to its longitudinal axis and in its cross section is provided.