WO2012045057A1

WO2012045057A1 - Bus transfer device

Info

Publication number: WO2012045057A1
Application number: PCT/US2011/054475
Authority: WO
Inventors: Julian Alexander Watt; Bradley Ryan Davis; Stephen Francis Peta
Original assignee: Dynapar Corporation
Priority date: 2010-10-01
Filing date: 2011-10-01
Publication date: 2012-04-05

Abstract

A compact, high reliability bus transfer device (40) for low voltage applications. The bus transfer device includes two vacuum contactors (42a, 42b) mounted together (48, 50) in a back-to-back arrangement such that the axes of the respective interlock arms (46a, 46b) are aligned with ends (54a, 54b) of the respective interlock arms proximate each other such that the interlock arms are prevented from being in their respective connected positions simultaneously by direct mechanical interference between the interlock arms. A spacer (44) disposed between the contactors provides a gliding surface to support the interlock arms during movement.

Description

BUS TRANSFER DEVICE

This application claims benefit of the 01 October 201 0 filing date of United States Application Number 61 /388,934.

FIELD OF THE INVENTION

This invention relates generally to the field of electrical contactors, and more particularly, to a low voltage bus transfer device incorporating two vacuum contactors. BACKGROUND OF THE INVENTION

A contactor is an electrically controlled switch used for switching a power circuit between connected and disconnected conditions. The contactor is part of the power circuit and it includes a contact mechanism which selectively connects or disconnects the input and output terminals of the contactor. The contact mechanism, in turn, is controlled by a control circuit which has a much lower power level than the switched power circuit. The control circuit selectively energizes the coil of an electromagnet to produce a magnetic field, which in turn attracts a movable core of the contact mechanism. A movable contact affixed to the movable core is propelled toward and held against a fixed contact by the magnetic field, thereby interconnecting the input and output terminals and connecting the power circuit. When the control circuit de- energizes the coil and the magnetic field is removed, the movable contact is returned to its original position by gravity or a spring, and the power circuit is disconnected.

Low voltage contactors (660 volts and less) are air break contactors; i.e. ordinary air surrounds the contacts and extinguishes the arc which is generated when the movable and fixed contacts are opened while conducting current by means of a sufficient open gap distance through air. Arcing can cause wear and eventual failure of the contacts, and its effects are more pronounced at high voltages, due to the requirement for additional open gap distance through air, so medium and higher voltage contactors (greater than 660 volts) use a vacuum or inert gas to surround the contacts, which does not support a sustained arc which in turn allows the contact gap distance to be minimized. An illustration of a typical prior art medium voltage vacuum contactor 10 is provided in FIG. 1 . The contactor 10 includes a housing 1 2, shown in partial sectional view, which contains the operating mechanism of the contactor 10, including a vacuum bottle 14 encompassing the contacts (not shown). An interlock arm 16 extends through an opening in the housing 12. The interlock arm 16 will move relative to the housing as the contactor 10 is switched between the connected and disconnected positions, for example, the interlock arm 16 will extend farther out of the housing 12 when the contactor 10 is moved to its connected position. A typical contactor 10 may have two interlock arms 16, with the second interlock arm not being visible in FIG. 1 because it is directly behind the illustrated interlock arm 16 in a direction into the plane of the drawing.

It is known in the art to use two contactors in cooperation with each other to form a bus transfer device. A bus transfer device allows a circuit to be switched from one power source to another without the possibility of both power sources being connected at the same time. The two contactors cooperate with each other by both being attached to a mechanical interlock mechanism 20, such as is illustrated in FIG. 2. The interlock mechanism 20 includes a mounting plate 22 to which the two cooperating contactors (not shown in FIG. 2 but as exemplified by FIG. 1 ) are mounted. In the embodiment of FIG. 2, the contactors 10 are mounted side by side (left and right) on the back side of the mounting plate 22 that is hidden from view in the figure. Each contactor 10 has two interlock arms 16 as described above which move together as the respective contactor is switched from its connected to its disconnected position. The contactors are mounted on the back side of the mounting plate 22 so that each interlock arm 16 is able to protrude through a respective slot 24 formed in the mounting plate 22. When a respective contactor is moved to its connected position, its interlock arm 16 moves farther through the respective slots 24 and engages opposed ends of a respective lever 26a or 26b. This action causes the respective lever 26a or 26b to rotate about its center pin 28a or 28b due to the interaction between the beveled ends of the interlock arms 16 and the lever 26a or 26b. Such movement is illustrated in FIG. 2 by arrows. A distal end 30a or 30b of the moving lever 26a or 26b is thus also moved.

FIG. 3 is an illustration of the distal ends 30a, 30b of the levers 26a, 26b in a position where a first of the contactors 10 mounted to the mounting plate 22 has been moved to its connected position, thereby rotating the distal end 30a of the lever 26a to an upper position, as indicated by the arrow in the figure. This position may be contrasted to the position of the distal ends 30a, 30b which is illustrated in FIG. 2 wherein both of the contactors 1 0 mounted to the mounting plate 22 are in their disconnected positions. It can be appreciated by viewing FIG. 3 that with the first of the contactors 10 in its connected position, the distal end 30b of the other lever 26b will be prevented from moving upward, thereby preventing the interlock arms 16 of the second of the contactors 10 mounted to the mounting plate 22 from being moved to the connected position, as indicated by the arrow covered by the X in FIG. 3. This provides a mechanical interlock which ensures that the second of the contactors 10 cannot be moved to its connected position while the first of the contactors 1 0 is already in its connected position, thereby preventing the two separate source supplies from connecting together, which would create the potentially very unsafe condition of shorting two separate power sources together.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of the drawings that show:

FIG. 1 is an illustration of a prior art electrical contactor.

FIG. 2 is a plan view of one prior art mechanical interlock mechanism for a bus transfer device or contactor pair.

FIG. 3 is a close view of a portion of the device of FIG. 2.

FIG. 4 is a cross-sectional illustration of an improved bus transfer device in accordance with one embodiment of the invention.

FIG. 5 is a close view of a portion of the device of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have recognized a need for an improved bus transfer device, and in particular one for low voltage applications. One embodiment of such an improved bus transfer device 40 is illustrated in FIG. 4, where two contactors 42a, 42b are mounted together in a base-to-base arrangement on opposed sides of one or more spacers 44. In this arrangement, the interlock arm(s) 46a, 46b of the two contactors 42a, 42b are aligned with each other along their respective axes of movement such that movement of either of the interlock arms (such as 46a) to its connected position will prevent the movement of the other of the interlock arms (such as 46b) to its connected position, thereby preventing simultaneous connection of two power sources to one load. This arrangement advantageously allows a direct mechanical interference to exist between the interlock arm(s) 46a, 46b of the two contactors 42a, 42b without the need for the mechanical interlock mechanism 20 of the prior art. The present invention therefore enables a bus transfer device 40 which is smaller, lighter, less expensive, more reliable and requires less maintenance than prior art devices.

In the embodiment of FIG. 4, the two contactors 42a, 42b may be of a known off- the-shelf design, and they are joined together with bolts 48 and nuts 50 through the aligned holes in the mounting feet 52a, 52b. One or more spacers 44 are positioned between the contactors 42a, 42b to allow for a small space 53 to exist between the opposed ends 54a, 54b of the interlock arms 46a, 46b when they are both in the disconnected position, as illustrated in FIG. 4.

FIG. 5 shows the position of the opposed ends 54a, 54b of the interlock arms 46a, 46b when one of the contactors 42a is moved to its connected position and the other contactor 42b is in its disconnected position. In this configuration, the small space 53 has been closed or nearly closed, and the end 54b of the disconnected contactor 42b is thereby prevented from moving, or severely limited in moving, thereby preventing the simultaneous connection of both contactors 42a, 42b. One skilled in the art will appreciate that the same mechanism will prevent the connection of contactor 42a once contactor 42b is connected.

In the embodiment of FIG. 4, at least one of the spacer(s) 44 is positioned proximate or surrounding the interlock arms 46a, 46b in order to provide a degree of mechanical support as well as a gliding surface which requires no lubrication to the arms as they move back and forth. In this embodiment, the spacers 44 may be nylon washers or other low friction material appropriate for the environment and capable of providing support to the interlock arms 46a, 46b without inhibiting their motion. The ends 54a, 54b of the interlock arms 46a, 46b may be used as they are provided by the original equipment manufacturer of the contactors 42a, 42b, or they may be fitted with a simple extension or specially shaped end piece (not shown) to facilitate their relative movement and the mechanical interference there between. One may appreciate that while the two axes of motion of the two interlock arms 46a, 46b may be described as being "aligned", that term is meant herein to include both co-linear alignment and a degree of misalignment that still provides the necessary amount of mechanical interference there between so that one of the arms in the connected position can prevent movement of the other arm to the connected position. One skilled in the art will also appreciate that embodiments of the invention may include contactors with interlock arms that move in a non-linear direction, wherein a mounting arrangement for the pair of contactors places the interlock arms into proximity to each other such that the interlock arms are prevented from being in their respective connected positions simultaneously by direct mechanical interference between the interlock arms.

The inventors have also recognized that the prior art practice of using vacuum contactors only for medium voltage applications or higher is too restrictive for certain low voltage applications (less than 660 volts) where a high degree of reliability is desired. In that regard, the contactors 42a, 42b of the present invention may be vacuum contactors for a low voltage application. The combination of the unexpected increase in reliability of a vacuum contactor being used in a low voltage application, along with the compact, reliable, low maintenance design of the present invention make it especially useful for particular applications. By incorporating vacuum contactors 42a, 42b and eliminating the complicated interlock mechanism 20 of the prior art, the present invention provides a compact, shock and vibration rugged, and reliable bus transfer device 40 which is particularly advantageous for Naval surface vessels or submarine applications, for example.

While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein.

Claims

The invention claimed is: 1 . A bus transfer device comprising:

a pair of contactors each comprising an extending interlock arm movable along an axis between a more extended position when the respective contactor is in a connected condition and a less extended position when the respective contactor is in a disconnected condition; and

the pair of contactors being mounted together in an arrangement such that the axes of the respective interlock arms are aligned with ends of the respective interlock arms proximate each other;

wherein when a first of the contactors is in its connected condition, the more extended position of its interlock arm is effective to prevent the interlock arm of a second of the contactors from moving to its more extended position from its less extended position, thereby preventing the two contactors from simultaneously being in the connected condition.

2. The bus transfer device of claim 1 , further comprising the pair of contactors being mounted in a back-to-back arrangement and separated by at least one spacer.

3. The bus transfer device of claim 2, wherein at least one spacer is positioned proximate or surrounding the interlock arms to provide a degree of mechanical support to the interlock arms as they move.

4. The bus transfer device of claim 3, wherein the at least one spacer comprises nylon.

5. The bus transfer device of claim 3, wherein the at least one spacer comprises a nylon washer surrounding the interlock arms.

6. A bus transfer device comprising:

a pair of contactors each comprising an interlock arm movable between a connected position and a disconnected position; and

a mounting arrangement for the pair of contactors placing the interlock arms into proximity to each other such that the interlock arms are prevented from being in their respective connected positions simultaneously by direct mechanical interference between the interlock arms.

7. The bus transfer device of claim 6, wherein the mounting arrangement comprises a back-to-back attachment of the pair of contactors effective to align the interlock arms along a common axis of movement.

8. The bus transfer device of claim 7, further comprising a spacer disposed between the pair of contactors, the spacer positioned proximate the interlock arms to provide a degree of mechanical support to the interlock arms as they move.

9. The bus transfer device of claim 8, wherein the spacer comprises a nylon washer surrounding the common axis of movement.

10. A bus transfer device for selectively connecting a load to either of two low voltage power sources, the bus transfer device comprising:

a pair of vacuum contactors each comprising an interlock arm movable along an axis between a connected position and a disconnected position, wherein in the connected position the respective vacuum contactor connects the load to a respective one of the low voltage power sources; and

the pair of vacuum contactors connected together in a base-to-base arrangement placing the respective interlock arms along a common axis;

wherein movement of either of the interlock arms to its connected position will prevent the movement of the other of the interlock arms to its connected position, thereby preventing simultaneous connection of the two power sources to the load.

1 1 . The bus transfer device of claim 10, further comprising a spacer disposed between the pair of vacuum contactors, the spacer providing a gliding surface for support of the interlock arms.