The invention relates to a device for connecting a first and a second busbar, which busbars are hollow and aligned with each other. In electrical installations, the power is typically distributed by busbars. Devices, like switch gear, plugs into these busbars to further distribute power to a subnet, a pump, an electric motor or the like. This switch gear is housed in cabinets (also called panels), which are placed next to each other. Busbars arranged in these cabinets or panels are connected to each other, such that the power is distributed from one panel to the other panel.

Another option is to position the panels first and then arrange single lengths of busbars in the panels. However, when a panel has to be exchanged or removed, one has to disassemble all the panels in order to take out the busbars and then to remove or exchange the panel. There are several methods for interconnecting busbars between panels. One of such options is by providing connecting elements. For flat strip busbars, the connecting elements can consist out of flat metal strips, which are bolted each with an end to one of the busbar ends of adjacent panels. Hollow tube like busbars can be connected by providing a busbar coupling, which slides over both ends of the adjacent busbars and provides an electrical connection. For a reliable connection, the ends of the busbars need to be machined such that a tight fit of the busbar coupling is possible. To exchange a panel or to remove a panel, one still needs to disassemble a number of panel or at least one needs to shift the number of panels in axial direction of the busbars, as some axial space is required to take out the busbar coupling on both sides of the panel to be exchanged.

The same applies for connecting a new panel. One needs to shift the panel in axial direction in order to shift the busbar connector over both ends of the busbars.

It is an object of the invention to provide a device for connecting two busbars, in which the above mentioned disadvantages are reduced or even removed. This object is achieved according to the invention with a device according to the preamble, which device comprises:

- an electrically conducting expansion member for arrangement inside the first busbar; - displacement means for displacing the expansion member in axial direction from the first busbar at least partially into the second busbar; and

- driving means for driving the displacement means and for driving the expansion of the expansion member.

With the device according to the invention, it is possible to first position a panel in its final position and then connect the busbars of the adjacent panels by controlling the driving means. The driving means will first move the expansion member partially into the hollow second busbar and then the expansion member is expanded inside the hollow first and second busbars to achieve a solid electrical connection of both busbars.

If a panel needs to be replaced or removed, the driving means could again be controlled in reverse direction, such that the expansion member is first contracted and then moved back into the first busbar. The panel can then easily be slid out of a row of panels.

In a preferred embodiment of the device according to the invention, the electrically conducting expansion member comprises:

- a sleeve having an outer surface corresponding to the internal surface of the first busbar, having on both ends of the inner surface wedge-shaped surface zones, and slits extending between the outer surface and the wedge-shaped surface zones; - axially movable wedge elements for cooperation with the wedge-shaped surface zones to press parts of the sleeve end outwardly in radial direction.

When the wedge elements are moved against the wedge-shaped surface zones, a radial force will be exerted on the sleeve causing the sleeve to expand. This expansion is further facilitated by providing slits extending between the outer surfaces and the wedge-shaped surface zones, such that resilient fingers are provided. Preferably, each slit extends from an end of the sleeve and has at least an axial directional component. The resilient fingers on the one end facilitate expansion, when the wedge elements are moved against the wedge-shaped surface zones, but they also facilitate contractions of the expansion element, such that the expansion element can easily be moved out of the second busbar by driving the driving means. In another embodiment of the device according to the invention the wedge elements are arranged on a threaded axle. When the axle is rotated by the driving means, the wedge elements can be translated. It is also possible to move two wedge elements in opposite directions by providing a right-handed thread portion and a left-handed thread portion and to arrange each of the wedge elements on one of the thread portions.

In another preferred embodiment of the device according to the invention the displacement means comprise telescopically arranged first and second shafts being provided with cooperating thread, wherein the first shaft is attached to the driving means and wherein the second shaft is attached to the expansion element.

With this embodiment the driving means can move the expansion element simply by providing a rotational drive to the first shaft. This will cause the first shaft to rotate relative to the second shaft and result in a telescopic movement of both shafts and a linear movement of the expansion element.

Preferably, the second shaft is the threaded axle. So, a simple rotational movement of the driving means will both cause the expansion element to move into the second hollow busbar and to expand inside the first and second busbars. The telescopic movement of the shafts will typically need less force, than the expansion of the expansion element. So, when the driving means are controlled the telescopic movement will be performed first until the shafts have reached an end position. The driving force will then be fully available for the expansion element.

In yet another embodiment, the driving means is an electric motor. An electric motor can easily be powered along thin wires, running through the hollow busbar and exiting at a suitable positioned, where the wires can be connected to a controller for the device according to the invention.

The electric motor could have a gear reduction. This will enable the use of a relative small electric motor, which can still produce sufficient power to drive the expansion element. These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a perspective view of an embodiment according to the invention. Figure 2 shows a cross-sectional view of the expansion element of figure 1.

Figures 3A - 3C show the device of figure 1 arranged in busbars in three positions.

Figure 1 shows a perspective view of an embodiment of a device 1 according to the invention. The device 1 has an expansion element 2, a displacement element 3 and an electric motor 4. The expansion element 2 has on both ends slits 5 to provide flexible fingers 6.

Figure 2 shows a cross-sectional view of the expansion element 2 of the device 1. The expansion element 2 has an internal surface with two wedge-shaped surface zones 7, 8.

The expansion element 2 furthermore has an axle 9 with a right-handed thread part 10 and a left-handed thread part 11. A first wedge element 12 is arranged on the right-handed thread part 10 and a second wedge element 13 is arranged on the left-handed thread part 11.

Figures 3A - 3C show the device 1 arranged in a first hollow busbar 14, which is aligned with a second hollow busbar 15. The displacement element 3 has an outer shaft 16 and an inner shaft 17 which are telescopic arranged.

As shown in figure 3B, the displacement element 3 moves the expansion element 2 partially into the second busbar 15, when the motor 4 rotates the outer shaft 16. When the end position as shown in figure 3B is reached, the outer shaft 16 will no longer rotate relative to the inner shaft 17. This can for example be achieved by providing a stop (not shown). The rotation of the motor 4 will then cause both rotate the inner shaft 17 and outer shaft 16, which in turn will rotate the axle 9. The rotation of the axle 9, in combination with the right-handed thread 10 and the left-handed thread 11 will cause the wedge elements 12, 13 to move towards each other.

When the wedge elements 12, 13 shift towards each other, they will get in contact with their respective wedge-shaped surface zones 7, 8 and provide a radial force by which the flexible fingers 6 are pressed outwardly and against the inner surfaces 18, 19 of the busbars 14, 15 respectively. This results in a reliable, firm, electrical and mechanical connection between the busbars 14, 15.

If the connection between the busbars 14, 15 needs to be removed, the motor 4 is controlled to rotate in the reverse direction, such that the wedge elements 12, 13 are moved away from each other and the fingers 6 can flex back, away from the inner surfaces 18, 19. Then by further rotating the motor 4, the displacement element 3 will pull the expansion element 2 inside of the first busbar 14 to arrive at the position shown in figure 3 A.