GB2040576A - Off-circuit tap selector for a transformer - Google Patents

Abstract

An off-circuit tap selector 60 comprises a contact carrier 19 supporting a plurality of spaced-apart fixed contacts 20 and a carrier member 16 supporting a movable contact 22, for bridging any two adjacent fixed contacts 20, the movable contact 22 being urged against the fixed contacts 20 by spring-biased means 61 comprising an element 62 which is pressed by a spring 67 away from the carrier member 16, and connecting means 66 connecting the element 62 to the carrier member 16 and which is rigid in all directions perpendicular to the line of action of the spring 67 so that it can withstand large forces applied to it in any of these directions. <IMAGE>

Description

SPECIFICATION An improved off-circuit tap selector This invention relates to an improved off-circuit tap selector which is specifically designed for use in oil, synthetic transformer insulating liquids or in air. In particular the invention relates to an offcircuit tap selector of the kind comprising a contact carrier supporting, in electrically insulating manner, a plurality of spaced-apart fixed contacts (for example arranged in a circle or a straight line), a movable contact (for example in the form of a ring) adapted to bridge between any two adjacent fixed contacts, a movable carrier comprising a carrier member movable relative to said fixed contacts to enable selection of the fixed contacts to be bridged by the movable contact, and spring-biased means urging said movable contact against said fixed contacts.

The present invention seeks to provide an offcircuit tap selector of the kind referred to in which the spring-biased means is able to withstand without damage, in use of the selector, forces transmitted thereto perpendicular to the direction of spring biasing.

According to the present invention an off-circuit tap selector comprises a contact carrier supporting, in electrically insulating manner, a plurality of spaced-apart fixed contacts, a movable contact adapted to bridge between any two adjacent fixed contacts, a movable carrier comprising a carrier member movable relative to said fixed contacts to enable selection of the fixed contacts to be bridged by the movable contact, and spring-biased means urging said movable contact against said fixed contacts and comprising a movable contact supporting element spaced from said carrier member and urged by spring means in a first direction away from said carrier member, and means connecting said movable contact supporting element to said carrier member, which connecting means is rigid in all directions perpendicular to the said first direction so that it can withstand large forces applied to it in the said directions perpendicular to the first direction without damage.

Suitably the movable contact is in the form of a ring having inner and outer cylindrical surfaces. In this case the supporting element typically comprises a cylindrical, or part-cylindrical, surface provided with spaced-apart end flanges, the cylindrical or part-cylindrical surface of the supporting element being urged by said spring means into contact with the inner cylindrical surface of the movable contact, the flanges serving to locate axially the annular end faces of the movable contact and being dimensioned to extend above the cylindrical, or part-cylindrical, surface of the supporting element a distance which is less than the difference in radius between the inner and outer cylindrical surfaces of the movable contact.Suitably the said connecting means consists of a rod, the opposite end portions of which are received in bores respectively provided in said carrier member and radially in said supporting element. Typically the spring means comprises a helical compression spring surrounding said rod and acting at one of its ends against a shoulder provided on the rod and at its other end against the supporting element.

The fixed contacts are conveniently arranged in a circle, in which case the carrier member is a rotatable shaft with its axis passing through the axis of the circle, and the said first direction is a radial directidn. It should however be realised that the fixed contacts may be arranged in a non circular configuration, for example in a straight line as disclosed in the complete specification of our co-pending Application No. 29405/77.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of a known off-circuit tap selector assembly, Figure 2 is an enlarged sectional view showing the off-circuit tap selector of the assembly shown in Figure 1, Figure 3 is an exploded perspective view, on a reduced scale, of part of the selector shown in Figure 2, Figure 4 is a sectional view, similar to the view shown in Figure 2, of an off-circuit tap selector according to the invention, Figures 5a, Sb and 6 show details on enlarged scales of the off-circuit tap selector shown in Figure 4, and Figure 7 is a sectional view of spring-biased means of another tap selector according to the invention.

A known off-circuit tap selector assembly is shown in Figure 1 and comprises a handle assembly, generally designated 1, and an offcircuit tap selector, generally designated 2.

The handle assembly 1 comprises a handle 50 having a shaft 3 and provided with a position indicator window 4 and a padlock hole 5, an indicator plate 6 provided with a plurality of holes 7 (only some of which have been designated reference numerals) arranged in a circle around a central hole 8, a bearing boss 9 fixed to the plate 6, adapted to be welded to the outside of a transformer tank (not shown) and having a central hole 10, annular seals 11 and 12, a spacer ring 13 and a handle coupling 14. The shaft 3 is adapted to pass through the hole 8 in the indicator plate 6, the seal 1 the hole 10 in the bearing boss 9, the seal 12, the spacer ring 13 and into one end of the coupling 14 to which it is connected by means of a splitpin 15.The other end of the coupling 14 has a square hole (not shown) into which is positioned a square shaft 16.

The shaft 1 6 is connected via a further coupling 1 7 to a rigid, electrically insulating tubular shaft 18 forming part of the selector 2. As can be seen from Figure 2, the selector 2 further comprises a contact carrier or board 19 moulded from a phenolic resin, carrying a plurality of fixed electrical contacts 20 arranged on a circle 21, and provided with a hole (not shown) at the centre of the circle 21, through which passes the shaft 1 6.

A movable contact ring 22 is arranged eccentrically of the shaft 1 6 (which passes through the ring 22) and is urged by spring-biased means, generally designated 23 in Figures 2 and 3, to bridge any two adjacent fixed contacts 20.

The spring-biased means 23 consist of a Ushaped carrier, generally designated 24, having a pair of spaced-apart parallel sides 25, 26 extending upwardly (as seen in Figures 2 and 3) from a connecting web 27. Each of the sides has a slot 28, 29, respectively, extending from its top to its bottom, the material forming the slots 28, 29 being bent downwardly (as seen in Figures 2 and 3) to provide two arms 30 and 31 which are located in holes 32 and 33, respectively, formed in the shaft 1 6. Another U-shaped carrier, generally designated 34, and having a pair of spaced-apart parallel sides 35, 36 extending upwardly (as seen in Figures 2 and 3) from a connecting web 37, is carried by the carrier 24, the sides 35, 36 being slidably received in the slots 28, 29, respectively.

The sides 35, 36 are each provided with a slot 38, 39, respectively, for locating stub shafts 40 (only one of which can be seen in Figures 2 and 3) of a roller 41. A helical compression spring 42 is positioned between the two connecting webs 27 and 37 and acts on the carrier 34 so that the roller 41 is pressed against an inner cylindrical surface 82 of the ring 22.

By manually rotating the handle 50 the shaft 1 6 is rotated causing the roller 41 to roll around the inner cylindrical surface 82 so that the ring 22 is moved with a snap action to make contact selectively with any adjacent pair of fixed contacts in the circle of fixed contacts 20.

The end portions of the sides 35, 36 of the carrier 34 are able to take up the relatively small forces normally applied to the ring 22 in a generally axial direction in use of the selector.

However, it is possible, although in practice extremely rare, for large axial forces to be applied to the ring 22, for example in the direction B in Figure 3 (or in the direction out of the paper in Figure 2), causing the carrier 34 to tilt or pivot about an axis formed along the junction of the web 37 with the side 35 until the carrier 34 is pivoted completely out of its operative sliding relationship with the carrier 24.

In order to overcome this problem an off-circuit tap selector according to the invention and generally designated 60 is shown in Figure 4. The selector 60 is similar in many respects to the selector shown in Figures 1 to 3 and the same reference numerals have been employed to identify similar parts of the two selectors.

The selector 60 differs from the selector shown in Figures 1 to 3 in the construction of springbiased means, generally designated 61, urging the ring 22 into bridging contact with any pair of adjacent fixed contacts 20. The spring-biased means 61 consists of a supporting element 62 (see Figures 5a and 5b) in the form of a cylindrical portion 63 having a pair of end flanges 64, 65, a solid, e.g. steel, rod 66 (see Figure 6) of circular cross-section, and a helical compression spring 67. The rod 66 has a stepped cross-section dividing the rod axially into four cylindrical portions 68, 69, 70 and 71 extending successively from one to the other end of the rod. The portions 68, 69 and 70 have successively larger diameters, and the portion 71 has a diameter between the diameters of portions 68 and 69.Annular shoulders 72, 73 and 74 are formed between the portions 68 and 69, 69 and 70, and 70 and 71, respectively. The end portion 71 of the rod 66 is received in a pair of diametrically opposed holes 75, 76 provided in the shaft 16, the holes 75, 76 having a diameter slightly greater than that of portion 71 but smaller than that of portion 70. The opposite end portion 68 is received in a blind radial hole 77 formed in the cylindrical portion 63 of the supporting element 62. The helical spring 67 is arranged around the rod 66 with one of its ends bearing against the shoulder 73 and its other end pressing against the circumferential surface of the portion 63 of the supporting element 62. In this way the portion 63 is urged in a radial direction by the spring 67 into contact with the inner cylindrical surface 42 of the ring 22.Since the rod 66 is rigid it can withstand large forces applied to it in any direction perpendicular to its axis. Axial forces applied to the ring 22 are taken up by inwardly facing annular surfaces of the flanges 64, 65 of the supporting element 62. In the embodiment described the difference in radius between each flange 64, 65 and the cylindrical portion 63 must be smaller than the difference in radius between the inner aid outer cylindrical surfaces of the ring 22 so that the flanges 64, 65 do not contact the fixed contacts 20 and prevent the cylindrical portion 63 from contacting the ring 22.It will be appreciated that since the supporting element 62 has a circular cross-section throughout its length, the cylindrical portion 63 can be easily and accurately manufactured, e.g. machine on a lathe or diecast, and thus the designed difference in diameter between the flanges and portion 63 can be accurately reproduced relatively cheaply and easily. (This simple and accurate manufacture of the element 62 contrasts with the manufacture of the U-shaped carrier 34 of the selector shown in Figures 1 to 3, which is difficult to manufacture cheaply to high tolerances.).

A pin 78 (see Figure 4) is provided in the shaft 1 6 to assist in axially locating the ring 22 during operation of the selector 60.

During operation of the selector 60 there is semi-sliding contact between the supporting element 62 and the ring 22 when the shaft 1 6 is rotated. Hence the ring 22 is turned about its own axis as the shaft 1 6 rotates causing the ring 22 to slide partially across the fixed contacts 20 thereby preventing build up of carbon deposits on the fixed and movable contacts. (This contrasts with the selector described with reference to Figures 1 to 3 where the same portions of the ring 22 contact the same fixed contacts 20 during each rotation of the shaft 16, thereby not rubbing away any carbon deposits which are formed on the fixed contacts 20 and at spaced apart locations around the ring 22 during use of the selector.) It will be appreciated that since the ring 22 of the selector 60 turns as the shaft 1 6 is rotated, the ring 22 could be replaced by a tiltable contact mounted on the element 62 or even, possibly, a contact fixed to, or integral with, the supporting element 62.

Furthermore, it will be realised that since only a part of the cylindrical portion 63 of the supporting element 62 contacts the ring 22, it is not necessary for the element 62 to have a circular cross-section. However, as mentioned previously, the circular cross-section of the element 62 is simple to manufacture and is generally preferred over other possible designs for the supporting element.

The selector 60 has been shown with seven fixed contacts 20. Other numbers of contacts 20 may, however, be provided for different voltage ratings, and the contacts 20 may be arranged in any suitable configuration (e.g. a circle or a straight line). When different numbers of contacts 20 are provided, the diameter of the circle 21 (or the length of the straight line joining the centres of the fixed contacts if the latter are arranged in a straight line) will be different In this event only the dimensions of the rod 66 of the spring-biased means 61 need be changed. The dimensions of the supporting element 62 and spring 67 will be the same whatever number of fixed contacts are provided, thereby minimizing production costs.

It will of course be realised that the springbiased means may be constructed in other ways.

For example Figure 7 shows an alternative construction for spring-biased means, generally designated 80, of another embodiment of a tap selector according to the invention The springbiased means 80 comprises a supporting element having a head portion 81 which contacts the contact ring 22 and a pin portion 82 extending from the head portion, a tubular member 83 having a flange 84 and provided with a bore 85 of slightly greater diameter than that of the pin portion 82, and a helical spring 86. The tubular member 83 is supported in the shaft 1 6 (note that the pin 78 shown fitted in the shaft 1 6 in Figure 4 has been omitted from Figure 7 for the purpose of clarity) with the pin portion 82 having a sliding fit within the bore 85. The helical spring 86 is arranged to surround the pin portion 82 with one end of the spring bearing against the head portion 81 and the other end of the spring bearing against the flange 84. The helical spring 86 thus acts to urge the supporting element in a radially outwards direction relative to the shaft 1 6. The sliding fit of the pin portion 82 within the bore 85 ensures that the spring biased means 80 is able to withstand comparatively large forces in directions perpendicular to the said radially outwards direction.

It will be appreciated that in each of the embodiments described the tap selector is designed so that the ring 22 gives a snap-action movement between tapping positions.

Claims (1)

1. An off-circuit tap selector comprises a contact carrier supporting, in electrically insulating manner, a plurality of space-apart fixed contacts, a movable contact adapted to bridge between any two adjacent fixed contacts, a movable carrier comprising a carrier member movable relative to said fixed contacts to enable selection of the fixed contacts to be bridged by the movable contact, and spring-biased means urging said movable contact against said fixed contacts and comprising a movable contact supporting element spaced from said carrier member and urged by spring means in a first direction away from said carrier member, and means connecting said movable contact supporting element to said carrier member, which connecting means is rigid in all directions perpendicular to the said first direction so that it can withstand large forces applied to it in the said directions perpendicular to the first direction without damage.

2. A tap selector according to claim 1, in which the movable contact is in the form of a ring having inner and outer cylindrical surfaces.

3. A tap selector according to claim 2, in which the said supporting element comprises a cylindrical, or part-cylindrical, surface provided with spaced-apart end flanges, the cylindrical or part-cylindrical surface of the supporting element being urged by said spring means into contact with the inner cylindrical surface of the movable contact, the flanges serving to locate axially the annular end faces of the movable contact and being dimensioned to extend above the cylindrical, or part-cylindrical, surface of the supporting element a distance which is less than the difference in radius between the inner and outer cylindrical surfaces of the movable contact.

4. A tap selector according to any of the preceding claims, in which the said connecting means consists of a rod, the opposite end portions of which are received in bores respectively provided in said carrier member and in said supporting element.

5. A tap selector according to claim 4, in which the spring means comprises a helical compression spring surrounding said rod and acting at one of its ends against a shoulder provided on the rod and at its other end against the supporting element.

6. A tap selector according to any of the preceding claims, in which the fixed contacts are arranged in a circle, the carrier member is a rotatable shaft with its axis passing through the axis of the circle, and the said first direction is a radial direction.

7. A tap selector according to any of claims 1 to 5, in which the fixed contacts are arranged in a straight line, and in which the carrier is movable in elongate directions parallel to said straight line.

8. A tap selector according to claim 7, in which the fixed contacts are arranged in more than one group in said straight line and the carrier has a separate carrier member extending perpendicular to said elongate directions for each of said groups, a separate movable contact and spring-biased means being associated with each of said carrier members.

9. A tap selector according to any of the preceding claims, in which the or each movable contact is designed to give a snap-action movement between tapping positions.

10. A tap selector constructed and arranged substantially as herein described with reference to Figures 4,5a,5b and 6 of the accompanying drawings.

11. A tap selector constructed and arranged substantially as herein described with reference to Figure 4 as modified by Figure 7 of the accompanying drawings.

New claims or amendments to claims filed on 16th May, 1980.

Superseded claims 1 and 2 New or amended claims: Original claims 3 to 11 renumbered as 2 to 10 and appendancies corrected.

1. An off-circuit tap selector comprises a contact carrier supporting, in electrically insulating manner, a plurality of spaced-apart fixed contacts, a movable contact in the form of a ring having inner and outer cylindrical surfaces, the outer cylindrical surface being adapted to bridge between any two adjacent fixed contacts, a movable carrier comprising a carrier member movable relative to said fixed contacts to enable selection of the fixed contacts to be bridged by the outer cylindrical surface of the movable contact, and spring-biased means urging said movable contact against said fixed contacts and comprising a movable contact supporting element spaced from said carrier member and urged by spring means in a first direction away from said carrier member against the inner cylindrical surface of the movable contact, and means connecting said movable contact supporting element to said carrier member, which connecting means is rigid in all directions perpendicular to the said first direction so that it can withstand large forces applied to it in the said directions perpendicular to the first direction without damage.