A FIXED CONTACT FOR A TAP CHANGER AND A METHOD FOR MOUNTING A CABLE LUG THERETO

Abstract

 The present invention relates to a fixed contact (1) arranged to be mounted on a wall (20) of a tap changer. The fixed contact (1) includes a contact part (4) and a cable connection part (7). The cable connection part (7) includes attachment means (13) for attachment to a cable lug.
According to the invention, the fixed contact (1) is arranged to be mounted to the wall (20) of the tap changer in such a way that at least the attachment means (13) is rotatable relative to the tap changer wall (20).
The invention also relates to a method for mounting a fixed contact to a wall of a tap changer, whereby the invented fixed contact is used.

Description

Field of invention

[0001] The present invention relates to a fixed contact arranged to be mounted on a wall of a tap changer, which fixed contact includes a contact part and a cable connection part, which cable connection part includes attachment means for attachment to a cable lug.

[0002] In a second and a third aspect, the invention relates to a tap changer provided with the invented fixed contact and to a transformer provided with the invented tap changer, respectively.

[0003] In a fourth aspect, the invention relates to a method for mounting a cable lug to a fixed contact in a tap changer.

Background of invention

[0004] A tap changer is commonly used in connection with a transformer in order to vary the transformation rate thereof. In a transformer with a tap changer, one of the windings in the transformer has a fixed amount of turns connected to the circuit. The other winding has one fixed connection point, whereas the other connection point can be selected among a number of contacts to attain a required voltage.

[0005] Upon a change in the load connected to the transformer or due to other influences it might be required to change the connection point. The need of changing the tap point is often triggered automatically in response to sensed parameters. Tap changing includes a plurality of manoeuvres including the opening and closing of switches e.g. via spring loaded energy accumulator and moving a fine selector arm to a new fixed contact. These manoeuvres have to be performed in a certain sequence and in a certain time relation.

[0006] Illustrative examples of tap selectors are disclosed e. g. in US 3652812, US 5374781, US 5523535, US 6849813, US 2010059356, EP 325139, DE 3936420, JP 63148607 and CN 101572174.

[0007] Generally, the cables from transformer windings are connected to the fixed contacts of the tap changer. Each fixed contact conventionally is provided with a mounting hole for this connection to which hole the cable lug of the winding is attached. The mounting hole has a fixed orientation, usually vertical or horizontal. However, normally the cables from the windings need to be connected from any direction. Thereby it will be necessary to bend the cable in order to fit the mounting hole of the respective fixed contact. The risk of bending cable is having a poor dielectric performance, may cause a high stress on fix contact or tap changer insulation materials and using non-standard cable lugs. It will also increase the difficulty and time for transformer production, when mounting the cables to the fixed contacts.

[0008] SE 13000708 discloses an example of how the connection of a cable lug to the fixed contact is facilitated. By arranging the mounting means of the fixed contact as a mounting screw perpendicular to the tap changer wall a certain freedom for the position of the cable lug is obtained, namely its angular position in a plane. By providing the cable with a cable lug where the plane of the lug forms an angle with the longitudinal centreline of the cable connection in the cable lug further flexibility regarding the mounting is obtained.

[0009] To obtain this higher degree of flexibility, however, requires that a set of cable lugs with various size of said angle is provided such that an appropriate one can be selected. This is somewhat unpractical and adds another step of complexity for the mounting operation. Furthermore the freedom of mounting direction will be complete only in one plane and limited to a very few in the perpendicular plane.

Summary of invention

[0010] The object of the present invention is to address the above described problem when mounting a cable to a fixed contact of a tap changer and thus allow a high freedom regarding the direction of the cable that is to be attached to the fixed contact and to achieve this in a simple way.

[0011] According to the first aspect of the invention this object is met in that a fixed contact for a tap changer of the kind specified in the preamble of claim 1 includes the specific features specified in the characterizing portion of the claim. The fixed contact thus is arranged to be mounted to the wall of the tap changer in such a way that at least the attachment means is rotatable relative to the tap changer wall.

[0012] Since the attachment means is rotatable in relation to the tap changer wall, the orientation of the attachment means can be freely chosen in a rotational plane. Thereby it can easily be adapted to the direction of the cable lug, and the cable lug can be attached to the attachment means without the need to bend the cable. Attaching the cable lug to the fixed contact thereby does not entail the problems discussed above and the mounting time will be reduced. Since the cable lug also can be attached to the attachment means at various directions in a plane perpendicular to the centre axis of the cable lug hole, a further degree of freedom is at hand for the attachment. It will also be possible to reduce the size of the transformer tank, since the invention enables reduction of required space for the cleats and leads arrangement because the more flexible connection of cables. The more flexible connection of cleats and leads is a result of the possibility to turn the mounting around two axes. The compact solution in two directions enables large distances between contacts, room to hide screws and enable paper winding of cable lug.

[0013] According to a preferred embodiment of the invention, the cable connection part includes a rotatable member including the attachment means, which rotatable member is rotatable relative to the contact part.

[0014] Thereby the contact part may be stationary and rigidly connected to the tap changer wall, which makes the contact more robust and more precise in the cooperation with the movable contact.

[0015] According to a further preferred embodiment, the rotatable member is rotatable mounted on a stationary member, which stationary member is rigidly connected to the contact part.

[0016] Thereby all main components of the fixed contact will be stationary relative to the tap changer wall, and only the member having the attachment means will be rotatable. This will further contribute to increase the stability and accuracy of the fixed contact

[0017] According to a further preferred embodiment, the rotatable member is arranged to be able to be rotated at least 360°.

[0018] By allowing rotation a complete turn the flexibility regarding the positioning of the mounting means will be optimized.

[0019] According to a further preferred embodiment the rotatable member is arranged to be positioned at a selected angular position selected among a limited plurality of possible positions.

[0020] It is normally not necessary for a convenient mounting that the rotational position is exactly adapted to the direction of the cable lug. In most cases it is sufficient with an approximate adaption. This allows a construction where the possible rotational positions are limited. The limited possible positions has the advantage of a clear structural layout of the cable connections.

[0021] According to a further preferred embodiment, the number of the possible positions is in the range of 6 to 36.

[0022] Within this range there will be the best balance between the requirement of high flexibility on one hand and clear structural layout on the other hand. Preferably the number of possible positions are within the range of 10 to 15, e.g. 12.

[0023] According to a further preferred embodiment, the possible positions are equally angularly distributed.

[0024] For a certain number of possible positions this equal distribution provides the best ability to adapt to the direction to the cable that is to be attached.

[0025] According to a further preferred embodiment, the rotatable member is angularly lockable relative to the stationary member at any selected position.

[0026] Thereby the connection will be securely maintained as mounted such that structural order is maintained which simplifies service, repair and replacement of a contact. The mounting thereby also will be less sensitive to vibrations. When there is a limited number of possible position the locking can be easily performed by snap-in devices.

[0027] According to a further preferred embodiment, the attachment means includes at least one through hole through the rotatable member.

[0028] Thereby the attachment means will be particularly adapted to cooperate with a cable lug for an easy attachment thereof.

[0029] According to a further preferred embodiment, the attachment means has a thickness in the area of the through hole that is sufficient large to allow attachment of a cable lug at each end of the through hole.

[0030] Since more than one cable often is to be attached to one and the same fixed contact this embodiment facilitates the mounting.

[0031] According to a further preferred embodiment, the stationary member includes second attachment means arranged to be able to be connected to a cable lug.

[0032] This allows a still further cable to be attached to the fixed contact, thus being advantageous when three cables are to be mounted to one and the same fixed contact.

[0033] According to the second aspect of the invention, the object is met in that a tap changer is provided with at least one fixed contact according to the present invention, in particular to any of the preferred embodiments thereof. Preferably a plurality of the fixed contacts or even all of them are according to the present invention.

[0034] According to the third aspect of the invention, the object is met in that a transformer is provided with a tap changer according to the present invention.

[0035] According to the fourth aspect of the invention, the object is met in that a method for mounting a cable lug to a fixed contact in a tap changer, includes the steps of

• providing a fixed contact according to the present invention, in particular to any of the preferred embodiments thereof,
• mounting the fixed contact to a wall of the tap changer
• rotating the attachment means to a selected angular position
• connecting the cable lug to the attachment means at the selected angular position.

[0036] The invented tap changer, the invented transformer and the invented method have advantages corresponding to those of the invented fixed contact and the preferred embodiments thereof, which advantages have been described above.

[0037] Preferred embodiments of the invention are specified in the dependent claims. It is to be understood that further embodiments may be constituted by any possible combination of features in the preferred embodiments specified above and by any possible combination of these features with features described in the following description of examples.

Brief description off the drawings

[0038] 

Fig.1 is a section through a tap changer wall with fixed contacts according to representative prior art.

Fig. 2 is a side view of a part of a fixed contact according to an example of the present invention.

Fig. 3 is an elevation view of a detail of fig. 2.

Fig. 4 is a schematic section through a fixed contact according to a further example of the invention.

Fig. 5 is a schematic section through a fixed contact according to a still further example of the invention.

Description of examples

[0039] Fig. 1 schematically illustrates a part of a tap changer according to representative prior art. The figure is a section through a part of the tap changer wall 120 perpendicular to the axis of the tap changer. On the tap changer wall there is mounted a plurality of fixed contacts which are distributed axialy as well as circumferentially on the tap changer wall. Only two of these fixed contacts 101 and 111 are shown in the figure.

[0040] The fixed contact 101 has a radially outer part 102 and a radially inner part 104. The inner part 104 is arranged to cooperate with a moving contact of the tap changer in response to what is required at the momentary operation condition. In the figure it is illustrated how the inner part 114 of the fixed contact 111 is connected to the moving contact 121.

[0041] The outer part 102 of the fixed contact is for stationary connection to a cable from the transformer winding. The cable lug is attached to the outer part by means of bolt and nut through the cable lug and the hole 103. The hole will be rigidly fixed in its orientation, whereby the initial drawbacks at mounting will occur.

[0042] The present invention generally is applicable to a tap changer of the type schematically illustrated in fig. 1, but with the exception that the cable connection part, i.e. the outer part will be rotatable.

[0043] Fig. 2 in a side view depicts a fixed contact 1 of a tap changer according to an example of the present invention. The fixed contact is mounted on the wall 20 of a tap changer. The contact part 4 is mounted on the inside of the tap changer wall 20 in a fixed relation thereto. The contact part 4 is to cooperate with a movable contact (not shown) in a way similar to what is described above in relation to fig. 1.

[0044] The cable connection part on the outside of the tap changer wall 20 has a rotatable member 10, which is rotatable around axis X around a stationary member (not visible in the figure). The stationary member is integral with the contact part 4. The rotatable member 10 has a sleeve portion 11 provided with a radial projection 12 with attachment means. The attachment means is a through hole 13 with a centre axis O extending in the tangential direction with regards to the rotation axis X. The cable lug is attached to the projection 12 by means of a nut and bolt through the hole 13 and the cable lug.

[0045] The rotatable member allows the projection 12 with its mounting means 13 to be positioned at a desired angular position around the rotation axis X adapted to the direction of the cable that is to be attached. Furthermore, the cable lug may be positioned at an adapted angular position around the centre axis O of the through hole 13. It will be possible to attach a first cable lug on the side of the projection facing upwards in the figure and a second cable lug on the opposite side.

[0046] In the illustrated example also a third cable lug may be attached to the fixed contact 1. The third cable lug will be attached between the washers 8 and cable connection part 7, then secured by a bolt 9 that is in engagement with a threaded bore of stationary member.

[0047] On each side of the tap changer wall 20 there is a shielding 5 and 6 of conventional kind.

[0048] In the illustrated example, the possible angular position are twelve at equal distribution, thus with an increment of 30°. At one end of the sleeve portion are twelve indentations 17 which represent the possible angular positions by cooperation with a snap-in mechanism (not shown) connected to the stationary member.

[0049] Fig. 3 illustrates the rotatable member 10 of the fixed contact, having a central hole 16 through which it is journalled on the stationary member. In the figure the indentation 17a is in the locking position. A cable lug may be attached to both sides 14, 15 of the projection 12.

[0050] In the above described example there is shown only one rotatable member 10. It is, however to be understood that more than one rotatable members may be present, which can be rotated independently of each other. It is also possible to arrange the single rotatable member with more than one radial projection with attachment means.

[0051] A further example of a construction of the invented fixed contact is schematically illustrated in fig. 4. In this example the complete part that is outside the tap changer wall 20, i.e. the cable connection side, is rotatable. The projection 10a with the attachment hole 13a is rigidly connected to a shaft 7a rotatable in a boring 61 in the contact part 6.

[0052] Fig. 5 schematically illustrates a still further example. The projection 10b with its attachment hole 13b is rigidly connected with the shaft 7b, and the latter is unitary with the contact part 6. The fixed contact includes a sleeve 21 in which all other parts of the fixed contact is rotatable. The sleeve 21 is fixedly attached to the tap changer wall 20. Alternatively the sleeve may be dispensed with, and the shaft 7b be arranged to be journalled for rotation directly in the hole in the tap changer wall 20.

Claims

1. A fixed contact (1) arranged to be mounted on a wall (20) of a tap changer, which fixed contact (1) includes a contact part (4) and a cable connection part (7), which cable connection part (7) includes attachment means (13) for attachment to a cable lug characterized in that the fixed contact (1) is arranged to be mounted to the wall (20) of the tap changer in such a way that at least said attachment means (13) is rotatable relative to the tap changer wall (20).

2. A fixed contact according to claim 1, wherein the cable connection part (7) includes a rotatable member (10) including said attachment means (13), which rotatable member (10) is rotatable relative to the contact part (4).

3. A fixed contact according to claim 3, wherein the rotatable member (10) is rotatable mounted on a stationary member, which stationary member is rigidly connected to the contact part (4).

4. A fixed contact according to claim 2 or 3, wherein said rotatable member (10) is arranged to be able to be rotated at least 360°.

5. A fixed contact according to any one of claims 2-4, wherein said rotatable member (10) is arranged to be positioned at a selected angular position selected among a limited plurality of possible positions.

6. A fixed contact according to claim 5, wherein the number of said possible positions is in the range of 6 to 36, preferably in the range of 10 to 15.

7. A fixed contact according to claim 6, wherein said possible positions are equally angularly distributed.

8. A fixed contact according to any one of claims 2-7, wherein the rotatable member (10) is angularly lockable relative to the stationary member at any selected position.

9. A fixed contact according to any one of claims 2-8, wherein said attachment means (13) includes at least one through hole (13) through the rotatable member (10).

10. A fixed contact according to claim 9, wherein said rotatable member (10) has a thickness in the area of the through hole (13) that is sufficient large to allow the attachment of a cable lug at each end of the through hole (13).

11. A fixed contact according to any one of claims 3-10, wherein said stationary member includes second attachment means (8, 9) arranged to be able to be attached to a cable lug.

12. A tap changer having fixed contacts mounted on a wall of the tap changer, wherein at least one of said fixed contact is a fixed contact according to any one of claims 1-11.

13. A transformer having a tap changer according to claim 12.

14. A method for mounting a cable lug to a fixed contact (1) in a tap changer, including the steps of

- providing a fixed contact (1) according to any of claims 1-11,

- mounting said fixed contact (1) to a wall (20) of the tap changer

- rotating said attachment means (13) to a selected angular position

- connecting the cable lug to said attachment means (13) at said selected angular position.

Drawing