GB2252682A

GB2252682A - High voltage transformer connector bushing

Info

Publication number: GB2252682A
Application number: GB9202225A
Authority: GB
Inventors: Alastair Wiliam Rictchi Thomas; Peter George Rampton
Original assignee: Hawker Siddeley Switchgear Ltd; London Electricity PLC
Current assignee: EDF Energy Ltd; Hawker Siddeley Switchgear Ltd
Priority date: 1991-02-02
Filing date: 1992-02-03
Publication date: 1992-08-12
Anticipated expiration: 2012-02-03
Also published as: GB2252682B; GB9202225D0

Abstract

A recessed support unit (12) for enabling electrical connection of, for example, a ring main unit to high voltage windings of a transformer housed in a casing, has a housing (44) of electrically insulating material. The housing of generally rectangular cross-section and has several pin connectors (18) sealingly extending through a base wall (17). The inner end (32) of each pin carries a number of spring biased blades (23) which engage with connector pins (21) of the ring main unit. The connector pins project through an open end of the housing (44) which lies opposite the base wall (17). The open end has a peripheral flange (13) by means of which the recessed support unit (12) is secured in a recess (11) in the wall of the transformer casing. The ring main unit is supported against the open end of the support unit (12) by mounting on studs (15) secured to the transformer casing. It is therefore a simple matter to change the ring main unit simply by undoing retaining nuts and moving the ring main unit away from the side wall of the transformer casing. There is no need partially to drain insulating oil from the transformer casing. <IMAGE>

Description

Title: Connector Arranqement This invention relates to an apparatus and a method of making an electrical connection to a high voltage transformer housed in a casing.

The core and windings of the transformer are housed in a transformer casing which in the use of the transformer is filled with oil to provide for cooling of the windings and also to act as an insulator. Associated with the transformer is a so called ring main unit which for each phase comprises a "T" connection having contactors in each limb. Two of the limbs in use are connected through the respective contactors into the ring main circuit and the third limb through the respective contactor to a phase connection of the transformer winding. In this way the transformer can be isolated from the ring main circuit and in addition, sections of the ring main can be isolated in conjunction with an adjacent unit.

It is known to mount the ring main unit on the casing of the transformer so that the bushings which support the third limbs of the connectors extend into the transformer casing, the windings being connected within the casing to the connectors respectively. The oil level within the casing lies above the bushings so that it provides the necessary electrical insulation.

A problem with this arrangement is that if it is required to change the ring main unit is it necessary to partly drain the casing of oil before removing and replacing the unit following which it is necessary to refill the transformer casing this process requiring testing of the oil to ensure the required electrical properties.

One known solution is to provide the transformer casing with bushings which support the connections to the transformer windings and to interconnect the ring main unit with the transformer casing using a hollow connection duct within which extends the bushings on the ring main unit and those on the transformer casing. The connections have to be effected using shaped links and are not particularly easy to achieve. Moreover, the length of the duct is such that it is necessary to provide a separate support for the ring main unit and as a result the overall dimensions of the transformer and the associated ring main unit are substantially increased. Nevertheless, the construction does have the advantage that it is not necessary to interfere with the transformer in order to change the ring main unit.

The object of the present invention is to provide an apparatus and a method of making the electrical connection to a high voltage transformer in a simple and convenient form.

Accordingly the present invention provides a device for enabling electrical connection to the high voltage windings of a high voltage transformer housed in a casing, the device comprising a housing having a base wall, at least one connector sealingly extending through said base wall for connection to a phase connection of said transformer, and flange means for enabling securing of said housing, within said transformer, to said transformer casing, wherein said flange means extends around an open end of said housing opposite said base wall for enabling connection of a terminal of an item of electrical equipment to said connector, and wherein said housing is formed from electrically insulating material.

Accordingly the present invention also provides a method of providing an electrical connection to the high voltage windings of a high voltage transformer housed in a casing comprises: providing an opening in a wall of the casing, and securing against the surface of said wall of the casing a recessed support unit which carries in its base wall at least one connection pin which in use is connected to a phase connection of the transformer, the recessed support unit being formed from electrically insulating material.

An example of an apparatus and method in accordance with the invention will now be described with reference to the accompanying drawing which shows a section through a portion of the side wall of a transformer casing.

A side wall of the casing of a transformer is indicated at 10 and formed in the side wall is an aperture 11 which conveniently is of rectangular form.

The aperture 11 is bounded by an outer wall 8 which carries a peripheral, outwardly extending flange 9 lying generally parallel to the transformer side wall 10. The flange 9, outer wall 8 and transformer side wall 10 are conveniently welded together to provide a seal to the insulating oil contained within the transformer casing.

Secured against the outer surface of the flange 9 is a recessed support unit 12 having a housing 44 which has a peripheral flange 13 secured against the outer surface of the flange 9 by means of nuts 14 engaged with studs 15 welded or otherwise secured to the flange 9. A gasket 16 is interposed between the flange and the surface of the side wall in order to prevent escape of insulating oil contained within the transformer casing.

The support unit is deeply recessed and the base wall 17 carries a connector pin 18 which extends on both sides of the base wall and is sealed therein to prevent escape of the oil within the transformer casing. The inner end 30 of the pin that is the end which is further from the side wall 10 of the casing, is provided with a screw thread whereby there can be secured to the pin a connector strap, the opposite end of which is connected to a phase connection of the high voltage winding of the transformer housed within the casing. The end 32 of the pin closer to the side wall 10 of the casing is chamfered.

The support unit 12 is formed from electrically insulating material which conveniently is of synthetic resin, conveniently of the epoxy type and the support unit may be formed as a casting. The material forming the support unit may be reinforced with glass fibre if so required.

The support unit carries three pins 18 and may have defined internal walls, not shown, to increase the length of the path between adjacent pins.

The studs 15 also serve to support a housing 40 of, for example, a switch box or ring main unit carrying, as described earlier, three contactors for each phase. The ring main unit has extending from its casing, three bushings 20 and each bushing accommodates a connector pin 21 which extends forwardly of the bushing. When the ring main unit is mounted on the transformer casing the pins 21 are in alignment with the respective pins 18 but are axially spaced therefrom. In order to effect an electrical connection between pins 18 and 21 each pin 18 carries a connector 22 which, as the ring main unit is moved into position, engages with the respective pin 21. The connector 22 has four blades 23 which are equally angularly spaced about the pin 18 and are spring loaded by respective springs 42 into engagement with the pins 18 and 21. The blades 23 are displaced outwardly against the action of the springs 42 as they engage the chamfered end of the pin 21.

The interior of the ring main unit will be filled with an insulating gas or oil but the interior of the support unit 12 is filled with air. It is thus a simple matter to change the ring main unit simply by undoing the retaining nuts and moving the ring main unit away from the flange 9 of the transformer casing.

There is no need partially to drain the insulting oil from the transformer casing and there is no need to charge the space within the support unit with either insulating gas or oil and as a result no specialised equipment is required in order to change the ring main unit. In order to prevent the ingress of moisture into the interior of the support unit, a further gasket 24 is interposed between the outer surface of the housing 40 of the ring main unit and the flange 13 of the support unit.

If desired, guide pins (not shown) may be moulded into the flange 13 of the support unit, the guide pins locating with apertures in the housing 40 of the ring main unit. The guide pins serve to guide the engagement of the connectors 22 with the pins 18.

As illustrated, plain flat gaskets are provided to effect the required seals. These however can be replaced by "0" ring type seals.

The bushing 20 is shown to be of plain cylindrical form. Its surface however can be provided with ribs in order to increase the length of path between the pin 21 and the wall of the casing.

Claims

1. A device for enabling electrical connection to the high voltage windings of a high voltage transformer housed in a casing, the device comprising a housing having a base wall, at least one connector sealingly extending through said base wall for connection to a phase connection of said transformer, and flange means for enabling securing of said housing, within said transformer, to said transformer casing, wherein said flange means extends around an open end of said housing opposite said base wall for enabling connection of a terminal of an item of electrical equipment to said connector, and wherein said housing is formed from electrically insulating material.

2. A device as claimed in claim 1 wherein said connector is formed with a screw-thread at one, outer end externally of said housing for connection to said phase connection of said transformer.

3. A device as claimed in claim 1 or 2 having a plurality of said connectors extending substantially parallel with one another.

4. A device as claimed in claim 2 or 3 wherein the or each said connector is in the form of a elongate pin whose longitudinal axis extends substantially perpendicular to the plane of said open end of the housing.

5. A device as claimed in any of the preceding claims wherein the or each said connector carries a plurality of spring-loaded blades at its inner end adjacent said open end of said housing for sliding engagement with said terminal of said item of equipment.

6. A method of providing an electrical connection to the high voltage windings of a high voltage transformer housed in a casing comprises: providing an opening in a wall of the casing, and securing against the surface of said wall of the casing a recessed support unit which carries in its base wall at least one connection pin which in use is connected to a phase connection of the transformer, the recessed support unit being formed from electrically insulating material.

7. A device for enabling electrical connection to high voltage windings of a high voltage transformer housed in a casing, the device being substantially as hereinbefore described with reference to the accompanying drawing.