GB2479524A

GB2479524A - Vacuum interrupter with earth terminal

Info

Publication number: GB2479524A
Application number: GB201005413A
Authority: GB
Inventors: Min Chen
Original assignee: Brush Transformers Ltd
Current assignee: Brush Transformers Ltd
Priority date: 2010-03-31
Filing date: 2010-03-31
Publication date: 2011-10-19
Also published as: GB201005413D0

Abstract

An electrical isolator comprises a fixed contact 107 and a longitudinally actuated contact 112 inside a mid section of an electrically insulating outer body 101 having an evacuated internal volume 106. When the fixed and moving contacts 107,112 are isolated from each other a flange 114, adjacent moving contact 112, engages with a conductive surface such as contact ring 115 that is connected to a terminal 104 extending form the mid section of the body. The third terminal may be used to earth the isolated circuit to provide safety upon isolation. The mid section of the body 101 can be a tubular transparent section, allowing the flange portion to be viewed (fig 7b). A hole (fig 7a, 742) through the moving contact 112 and aligned with the transparent section can allow a the position of the moving contact to be detected by light emitting and receiving elements (fig 7c, 743,744). A pair of guide rollers (fig 3, 331a,b) on the outer portion of the flange that mechanically contact the inner surface of the body may run in recesses and provide alignment of the contacts. The guide rollers can be toothed pinions (fig 4, 431a,b) engaging with a rack on the inner surface of the body. The isolator may comprise a similar second isolator (fig 6, 550), mechanically and electrically attached to it, to provide additional security should the vacuum fail in either.

Description

ELECTRICAL ISOLATOR

The invention relates to electrical isolators, in particular to a type of isolator incorporating an evacuated internal volume for preventing arcing during connection and disconnection of high voltage supplies.

In electrical engineering, an electrical isolator is used to make sure that an electrical circuit can be completely de-energized for service or maintenance. High-voltage electrical isolators are used in electrical substations to allow isolation of apparatus such as circuit breakers, transformers or transmission lines for maintenance. Often the isolator is not intended for normal control of the circuit and is instead only used for isolation as well as being an off-load device, i.e. being intended to be opened only after current has been interrupted by some other control device, except in an emergency, for example when the main circuit breakers fail in operation. In many designs the electrical isolator has the additional ability to earth the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits for interconnect power distribution systems, where both ends of the circuit would need to be isolated.

US 4,492,837 discloses an exemplary electrical isolator known as a vacuum interrupter, comprising an end plate having a central opening through which a movable contact rod extends. A tubular metallic bellows surrounds the contact rod to allow movement of the contact rod while maintaining a vacuum within the isolator. The movable rod contacts a stationary contact rod extending through an opening in an upper end cap.

Electrical isolators of the type disclosed in US 4,492,837 may also be configured to connect a movable contact to one or two stationary contacts, as for example disclosed in WO 01/50562, in which a modular three position vacuum isolator is operable to connect a movable contact to either of two stationary contacts or to an intermediate position which is out of electrical engagement with either of the stationary contacts.

In adding further contacts to an electrical isolator, however, known solutions tend to result in more complicated and larger assemblies. A problem with known isolator solutions is therefore how to maintain a small size while offering the ability to switch between more than two electrical terminals, for example to switch a first terminal from being contacted with a second terminal to being contacted to a third terminal, which may for example be a ground (or earth) terminal.

It is an object of the invention to address one or more of the above mentioned problems.

In accordance with the invention there is provided an electrical isolator assembly comprising: an electrically insulating outer body having a first terminal at a first end of the body, a second terminal at an opposing second end of the body and a third terminal extending from a mid-section of the body, the mid-section comprising an evacuated internal volume; a first electrical contact fixed relative to the outer body and extending within the body from a proximal end at the first terminal to a distal end at the mid-section of the body; a second electrical contact extending within the body from a proximal end at the second terminal to a distal end at the mid-section of the body and configured to actuate along a longitudinal axis of the body between a first position in which the distal end of the second electrical contact is in electrical contact with the distal end of the first electrical contact and a second position in which the distal end of the second electrical contact and the distal end of the first electrical contact are isolated from each other by a portion of the internal evacuated volume, wherein the second electrical contact comprises a laterally extending electrically conductive flange portion adjacent the distal end and disposed within the evacuated volume, the outer body comprising an internal conductive surface in contact with the third terminal that is configured to engage with the flange portion when the second electrical contact is in the second position and thereby provide an electrical connection between the second and third terminals.

The laterally extending flange portion allows the movable second electrical contact to perform the functions of both disconnecting and connecting with the first electrical contact and connecting and disconnecting with the internal conductive portion in contact with the third terminal in a single movement. This results in an electrical isolator that is compact while maintaining the additional functionality of being able to ground the second terminal when actuated as well as break a connection between the first and second terminals.

The mid-section of the body may comprise a transparent portion for viewing the flange portion when the second electrical contact is in the first or second position. An advantage of this feature is that the state of the isolator can be readily visually inspected by viewing the position of the movable second contact. The transparent portion may be provided by a tubular section extending across the mid-section of the body, the tubular section being made for example from an electrically insulating transparent material such as glass.

The second electrical contact may comprise a hole passing transversely therethrough and aligned with the transparent portion of the body. This has the advantage of enabling ease of inspection by viewing whether light is visible through the hole.

The electrical isolator assembly may comprise a light emitting element and a light receiving element aligned on opposing sides of the transparent portion such that a direct line of sight is formed between the light emitting element and the light receiving element only when the second electrical contact is in the first position or in the second position.

This has the advantage that an electrically isolated circuit can be formed that provides an indication of the state of the isolator assembly, allowing remote monitoring of the state of the assembly.

The light emitting element and light receiving element may be aligned with a hole passing through the second electrical contact such that the direct line of sight is provided through the hole only when the second electrical contact is in the first position or the second position. This has the advantage that a clear signal is obtained of the state of the isolator, indicated by whether light is received by the light receiving element from the light emitting element.

The internal conductive surface of the outer body may comprise a contact ring configured to engage with the flange portion when the second electrical contact is in the second position. The contact ring ensures a substantial contact area for connecting with the flange portion with a minimum cross-section.

The flange portion may comprise a pair of guide rollers rotatably mounted on an outer edge of the flange portion and in mechanical contact with an inner surface of the mid-section of the body. The guide rollers ensure that movement of the second terminal is smooth and reliable, and minimises tilting or bending of the contact if movement is actuated unevenly or off-axis. The guide rollers may each comprise a pinion engaged with a rack on the inner surface of the mid-section of the body, or may be smooth rollers engaged with a corresponding smooth planar inner surface of the mid-section of the body.

The internal conductive surface of the body may comprise a pair of recesses configured to receive the pair of guide rollers when the second electrical contact is in the second position. This has the advantage of reducing the overall length of the assembly while maintaining a sufficient contact area for connecting the third terminal with the second terminal.

The outer body may be of a generally tubular construction, comprising a first electrically insulating tubular section extending from the first terminal to the mid-section, a second electrically insulating tubular section extending from the second terminal to the mid-section and a third tubular section having a larger diameter than the first and second tubular sections extending across the mid-section.

According to an alternative embodiment of the invention there is provided an electrical isolator assembly comprising a first electrical isolator according to any one of the above described isolator assemblies and a second electrical isolator assembly comprising: an electrically insulating outer body having a first terminal at a first end of the body in electrical contact with the first terminal of the first electrical isolator assembly and a second terminal at an opposing second end of the body, the body comprising an evacuated internal volume; a first electrical contact fixed relative to the outer body and extending within the body from a proximal end at the first terminal to a distal end to the evacuated internal volume; a second electrical contact extending within the body from a proximal end at the second terminal to a distal end at the evacuated internal volume and configured to actuate along a longitudinal axis of the body between a first position in which the distal end of the second electrical contact is in electrical contact with the distal end of the first electrical contact and a second position in which the distal end of the second electrical contact and the distal end of the first electrical contact are isolated from each other by a portion of the internal evacuated volume.

An advantage of adding a second electrical isolator is that two separate vacuums provide redundancy in forming an electrical disconnection between the second electrical contact of the first assembly and the second electrical contact of the second assembly, so that in case of failure of one of the vacuums the assembly is still operable.

Aspects and embodiments of the invention are described in further detail below by way of example and with reference to the enclosed drawings in which: figure la is a perspective cut-away view of an exemplary electrical isolator assembly according to a first embodiment; figure lb is a cross-section view of the isolator assembly of figure la; figures 2a, 2b and 2c are cross-section views of the isolator assembly of figure 1 in a connected, disconnected and grounded position, respectively; figure 3a is a perspective cut-away view of an exemplary electrical isolator assembly according to a second embodiment; figure 3b is a cross-section view of the isolator assembly of figure 3a; figure 3c is a cross-section view of a roller assembly portion of the isolator assembly of figures 3a and 3b; figure 4a is a perspective cut-away view of an exemplary electrical isolator assembly according to a third embodiment; figure 4b is a cross-section view of the isolator assembly of figure 4a; figure 4c is a cross-section view of a roller assembly portion of the isolator assembly of figures 4a and 4b; figure 5a is a perspective cut-away view of an exemplary electrical isolator assembly according to a third embodiment; figure 5b is a cross-section view of the isolator assembly of figure 5a; figures 6a, 6b and 6c are cross-section views of the isolator assembly of figure 5 in a connected, disconnected and grounded position, respectively; figure 7a is a cross-section view of an exemplary electrical isolator assembly according to a fourth embodiment; figure 7b is a first transverse cross-section view of the assembly of figure 7a; and figure 7c is a second transverse cross-section view of the assembly of figure 7a.

Shown in figures la and lb is an first exemplary embodiment of an electrical isolator assembly 100 having an electrically insulating outer body 101 comprising a first terminal 102 at a first end of the body, a second terminal 103 at an opposing end of the body 101 and a third terminal 104 extending from a mid-section 105 of the body 101. The mid-section 105 of the body 101 comprises an evacuated internal volume 106. A first electrical contact 107 in the form of a rod that is fixed relative to the body 101 and extends within the body 101 from a proximal end 108 at the first terminal 102 to a distal end 109 at the mid-section 105 of the body 101. A second electrical contact 110 in the form of a movable rod extends within the body 101 from a proximal end 111 at the second terminal 103 to a distal end 112 at the mid-section 105 of the body 101.

The outer body 101 of the electrical isolator assembly 100 is of a generally tubular construction, the outer body comprising a first electrically insulating tubular section lOla extending from the first terminal 103 to the mid-section 105, a second electrically insulating tubular section lOib extending from the second terminal 102 to the mid-section and a third electrically insulating tubular section 101c having a larger diameter than the first and second tubular sections lOla, lOib extending across the mid-section 105.

The first tubular section lOla is sealed at one end by an end lid 120 and end cover 121, through which the proximal end 111 of the movable second contact 110 passes. An anti-twisting nut 122 engages with the proximal end 111 of the movable second contact 110 to prevent rotation of the contact 110. The second tubular section lOib is sealed at one end by an end cover 123 and end lid 124, the second terminal 102 extending from the end lid 124.

The first and second tubular sections lOla, lOib are preferably made from an insulating ceramic material, while the third tubular section lOic is preferably made from glass, to enable the internal components of the mid-section 105 to be viewed in use.

The second tubular section lOib is connected to the third tubular section by a first connecting portion 125 that seals against both sections and reduces from the larger diameter of the third section lOic to the second section bib. Similarly, a second connecting portion 126 is provided between the first and third tubular sections lOla, lOic.

The second connecting portion 126 joins the third terminal 104 to a contact ring 117 in the mid-section 105 of the body 101, and is therefore preferably made from an electrically conductive material. The first connecting portion 125 may also be made from an electrically conductive material, provided it is sufficiently well insulated from the first and second contacts 107, 110.

The electrical isolator assembly 100 of figures la and lb is illustrated further in cross-section in figures 2a-c, which show the movable second electrical contact 110 in three positions: a first position (figure 2a) in which the first and second electrical contacts 107, are in electrical contact with each other, a second position (figure 2c) in which the first and second electrical contacts 107, 110 are disconnected from each other and the second electrical contact is electrically connected to the third terminal 104, and a third intermediate position (figure 2b) in which the second electrical contact 110 is disconnected from both the first contact 107 and the third terminal 104, i.e. midway between the first and second positions. As can be seen in figures 2a-2c, the second electrical contact 110 is configured to actuate along a longitudinal axis 113 of the body 101 between the first position (also shown in figures la and ib) in which the distal end 112 of the second electrical contact 110 is in electrical contact with the distal end 109 of the first contact 107 and the second position (figure 2c) in which the distal end 109 of the first electrical contact 107 and the distal end 112 of the second electrical contact 110 are isolated from each other by a portion of the internal evacuated volume 106.

The second electrical contact 110 comprises a laterally extending electrically conductive flange portion 114 adjacent the distal end 112 and disposed within the evacuated volume 106, the flange portion 114 extending transverse to the longitudinal axis 113. The outer body 101 comprises an internal conductive surface 115 in contact with the third terminal 104, the internal conductive surface 115 being configured to engage with a corresponding surface 116 of the flange portion 114 when the second electrical contact 110 is in the second position (figure 2c) and thereby provide an electrical connection between the second 103 and third 104 terminals. In the embodiment shown, the internal conductive surface 115 of the outer body 101 comprises a contact ring or grounding disc 117 As with known vacuum isolators, the movable second contact 110 is connected to the body via bellows 119, which allows the second contact 110 to move axially while maintaining a vacuum within the mid-section 106 of the body 101. A shield 127 is provided around the bellows, and shields 128, 129 are also provided around the fixed first contact 107.

A problem with the above construction is that of ensuring proper alignment of the second electrical contact 110, particularly when the contact returns to the position in figure 2a to engage with the first contact 107. If the distal end 112 of the second contact 110 moves out of alignment with the axis 113 of the body 110, the contact may not properly engage with the first contact.

To address the above problem, second and third exemplary embodiments of an electrical isolator assembly 300, 400, illustrated in figures 3 and 4, comprise a flange portion 314 that comprises a pair of guide rollers 331a, 331b rotatably mounted on pins 332a, 332b affixed to an outer edge of the flange portion 314, the guide rollers 331a, 331b in mechanical contact with an inner surface of the mid-section 301c of the body of the assembly 300. In the second exemplary embodiment, illustrated in figure 3, the pair of guide rollers 331a, 331b are in the form of roller bearings that engage with a planar track portion on the inner surface of the mid-section of the body, as shown in more detail in the cross-sectional views of figure 3c.

A possible disadvantage of the use of circular guide rollers as shown in figure 3 is that of electrical creep along a path connecting the moveable second electrical contact 310 with the contact ring 317. In a vacuum, direct electrical clearances can be reduced considerably compared with air or inert gas-filled isolators, but electrical creep distances may not be affected. In order to address this possible problem, in the third exemplary embodiment of electrical isolator assembly 400, illustrated in figure 4, the pair of guide rollers 431a, 431b are in the form of pinions rotatably mounted on pins 432a, 432b affixed to the outer edge of the flange portion 414 of the movable second contact 410, the pinions 431a, 431b being engaged with respective racks 433a, 433b on the inner surface of the mid-section 401c of the body of the assembly 400. An advantage of the guide rollers being in the form of pinions, or toothed gears, engaged with a corresponding rack is that the electrical creep distance, being the shortest distance between two electrically conductive parts along the surface of an intervening insulator, i.e. between the electrically conducting part of the flange portion 414 and any other electrically conductive component (such as the contact ring 417), is extended compared with circular guide rollers as in figure 3. The electrical breakdown resistance of the device is therefore improved further, allowing the device to be used at higher voltages or, alternatively, for the device to be made smaller for use at the same voltage.

In each of the above second and third embodiments, the guide rollers reduce or prevent lateral movement of the distal end of the second contact 310, 410, thereby ensuring proper axial alignment of the second contact. The use of guide rollers 331a,b, 431a,b also allows for a longer distance between the distal ends of the first and second contacts when in the grounded position (as in figure 2c), thereby allowing the electrical isolator assembly 300, 400 to be designed for higher operating voltages. Whereas the assembly according to the first embodiment would typically be designed to operate at voltages up to 12 kV, the assemblies 300, 400 according to the second and third embodiments may be designed to operated at 72.5 kV or even up to 252kV or higher, because the gap between the contacts when disconnected can be made greater without sacrificing reliability of the assembly.

In order to accommodate the guide rollers 331a,b, 431a,b in the assemblies 300, 400 according to the second and third embodiments, the contact ring 317, 417 is provided with recesses 334a,b, 434a,b that are configured to receive the pair of guide rollers 331a,b, 431a,b when the second electrical contact 310, 410 is in the second position, with the flange portion 317, 417 electrically connected with the contact ring 317, 417.

The remaining components of the assemblies 300, 400 according to the second and third embodiments may be similar to those of the assembly 100 according to the first embodiment, as indicated by the corresponding reference numerals used.

A fourth exemplary embodiment of an electrical isolator assembly 500 is illustrated in figure 5, in which a second isolator 550 is mechanically and electrically attached to a first terminal 102 of a first isolator 540. The first isolator 540 is substantially similar to the isolator 100 according to the first embodiment, although the features of the second and third embodiments may alternatively be used. The second isolator 550 comprises an electrically insulating outer body 551 having a first terminal 552 at a first end of the body in electrical contact with the first terminal 102 of the first electrical isolator assembly 540 and a second terminal 553 at an opposing second end of the body 551. The body 551 comprises an evacuated internal volume 556.

The second isolator 550 comprises a first electrical contact 557 fixed relative to the outer body 551 and extending within the body from a proximal end 558 at the first terminal 552 to a distal end 559 within the evacuated internal volume 556 of the body. A second electrical contact 560 extends within the body 551 from a proximal end 561 at the second terminal 553 to a distal end 562 within the evacuated internal volume 556 of the body.

The second electrical contact 560 is configured to actuate along a longitudinal axis 563 of the body between a first position (figure 6a) in which the distal end 562 of the second electrical contact 560 is in electrical contact with the distal end 559 of the first electrical contact 557 and a second position (figure 6c) in which the distal end 562 of the second electrical contact 560 and the distal end 559 of the first electrical contact 507 are isolated from each other by a portion of the internal evacuated volume 556.

Figures 6a, 6b and 6c also illustrate the first isolator 540 in first, second and third positions that correspond to the positions shown in figures 2a-c relating to the isolator 100 of the first embodiment. With the isolator 500 according to the fourth embodiment, the second isolator 550 provides for additional security against failure of the assembly 500 in case of vacuum failure, since the assembly 500 will still be able to operate to disconnect the first terminal 102 of the first isolator 540 from the second terminal 553 of the second isolator if the vacuum fails in one of the isolators 540, 550.

Figure 7 illustrates a fifth embodiment of an electrical isolator assembly 700, in which modifications to the movable second electrical contact 707 are made to allow for ease of inspection and automated inspection of the connection state of the assembly 700 compared with the assembly 100 according to the first embodiment. Figure 7a is a section along the longitudinal axis 113 of the assembly 700, figure 7b is a section along the plane indicated by line A-A in figure 7a, and figure 7b is a further section along the plane indicated by line B-B in figure 7b.

The moveable second contact 710 in the embodiment shown in figure 7a comprises holes 741, 742 that pass transversely through the contact 710 and are aligned with a transparent portion lOic of the outer body, i.e. the mid-section that surrounds the flange portion 714 of the contact 710. Either of the holes 741, 742 allow for inspection of the position of the second contact 710 in relation to the outer body lOic, either by eye (indicated in figure 7b) or through the use of an optical detection system (indicated in figure 7c). A first larger one 741 of the holes allows for inspection by eye, for example by comparing one or more marks on the outer body lOic with a position of the hole 741. A second one 742 of the holes is, with the contact 710 in one of the first or second positions (see figures 2a and 2c), aligned with a light emitting element 743 and a light receiving element 744 located on opposing sides of the body lOic. If the light emitting and receiving elements 743, 744 are aligned with the hole 742 when the contact 710 is in the second position, a signal from the light receiving element 744 will indicate that the assembly is in a disconnected state, with the first and second terminals 102, 103 disconnected and the second terminal 103 connected to the third terminal 104.

Alternatively, the light emitting and receiving elements 743, 744 may be aligned with the hole when the contact 710 is in the first position, a signal from the light receiving element 744 indicating that the assembly is in a connected state, with the first and second terminals 102, 103 connected and the third terminal 104 disconnected. The light emitting element may for example comprises a light emitting diode or laser while the light receiving element may comprise an optical detector such as a light-dependent resistor or a light sensitive diode.

The alternative features of the second to fourth embodiments may also be incorporated into the assembly 700 according to the fifth embodiment.

Other embodiments are also within the scope of the invention, which is defined by the appended claims.

Claims

CLAIMS1. An electrical isolator assembly comprising: an electrically insulating outer body having a first terminal at a first end of the body, a second terminal at an opposing second end of the body and a third terminal extending from a mid-section of the body, the mid-section comprising an evacuated internal volume; a first electrical contact fixed relative to the outer body and extending within the body from a proximal end at the first terminal to a distal end at the mid-section of the body; a second electrical contact extending within the body from a proximal end at the second terminal to a distal end at the mid-section of the body and configured to actuate along a longitudinal axis of the body between a first position in which the distal end of the second electrical contact is in electrical contact with the distal end of the first electrical contact and a second position in which the distal end of the second electrical contact and the distal end of the first electrical contact are isolated from each other by a portion of the internal evacuated volume, wherein the second electrical contact comprises a laterally extending electrically conductive flange portion adjacent the distal end and disposed within the evacuated volume, the outer body comprising an internal conductive surface in contact with the third terminal that is configured to engage with the flange portion when the second electrical contact is in the second position and thereby provide an electrical connection between the second and third terminals.
2. The electrical isolator assembly of claim 1 wherein the mid-section of the body comprises a transparent portion for viewing the flange portion when the second electrical contact is in the first or second position.
3. The electrical isolator assembly of claim 2 wherein the transparent portion is provided by a tubular section extending across the mid-section of the body.
4. The electrical isolator assembly of claim 2 or claim 3 wherein the second electrical contact comprises a hole passing transversely therethrough and aligned with the transparent portion of the body.
5. The electrical isolator assembly of claim 2 or claim 3 comprising a light emitting element and a light receiving element aligned on opposing sides of the transparent portion such that a direct line of sight is formed between the light emitting element and the light receiving element only when the second electrical contact is in the first position or in the second position.
6. The electrical isolator assembly of claim 5 wherein the light emitting element and a light receiving element are aligned with a hole passing through the second electrical contact such that the direct line of sight is provided through the hole only when the second electrical contact is in the first position or the second position.
7. The electrical isolator of any preceding claim wherein the internal conductive surface of the outer body comprises a contact ring configured to engage with the flange portion when the second electrical contact is in the second position.
8. The electrical isolator of any preceding claim wherein the flange portion comprises a pair of guide rollers rotatably mounted on an outer edge of the flange portion and in mechanical contact with an inner surface of the mid-section of the body.
9. The electrical isolator of claim 8 wherein the guide rollers each comprise a pinion engaged with a rack on the inner surface of the mid-section of the body.
10. The electrical isolator of claim 8 or claim 9 wherein the internal conductive surface of the body comprises a pair of recesses configured to receive the pair of guide rollers when the second electrical contact is in the second position.
11. The electrical isolator of any preceding claim wherein the outer body comprises a first electrically insulating tubular section extending from the first terminal to the mid-section, a second electrically insulating tubular section extending from the second terminal to the mid-section and a third tubular section having a larger diameter than the first and second tubular sections extending across the mid-section.
12. An electrical isolator assembly comprising a first electrical isolator according to any preceding claim and a second electrical isolator assembly comprising: an electrically insulating outer body having a first terminal at a first end of the body in electrical contact with the first terminal of the first electrical isolator assembly and a second terminal at an opposing second end of the body, the body comprising an evacuated internal volume; a first electrical contact fixed relative to the outer body and extending within the body from a proximal end at the first terminal to the evacuated internal volume; and a second electrical contact extending within the body from a proximal end at the second terminal to a distal end in the evacuated internal volume and configured to actuate along a longitudinal axis of the body between a first position in which the distal end of the second electrical contact is in electrical contact with the distal end of the first electrical contact and a second position in which the distal end of the second electrical contact and the distal end of the first electrical contact are isolated from each other by a portion of the evacuated internal volume.
13. An electrical isolator assembly substantially as described herein, with reference to the accompanying drawings.