Field of the invention

The invention relates to a magnetic actuator unit for a circuit breaker arrangement comprising an armature arranged to be movable between a first and a second end position for an opened and a closed switching position respectively of a circuit-breaker, a single electrical coil for moving the armature to the second position due to electrical current feed, a permanent magnet for additionally loading the armature in the direction of the second position, an outer ferromagnetic yoke at least partly surrounding the single electrical coil and the ferromagnetic core for directing the magnetic flux to the movable ferromagnetic armature, an opening spring means for permanently loading the armature in the direction of the first position, which is coaxially arranged between the armature and the front side of the electrical coil.

For operation of a circuit-breaker, especially a medium-voltage vacuum circuit-breaker, it is required to generate a high force to press a moving electrical contact to a corresponding fixed electrical contact. This force can be generated by a magnetic actuator unit. Both electrical contacts are usually integrated in a pole part for insulating purpose wherein the movable electrical contact is operated by the magnetic actuator unit via a jackshaft arrangement. The jackshaft arrangement usually drives more than one pole part. For a 3-phase power grid circuit-breaker application the jackshaft arrangement drives three pole parts by a single magnetic actuator unit.

The document WO 2008/119785 A1 discloses a magnetic actuator unit for a circuit- breaker having a first electrical coil, a second electrical coil and an armature arranged to be moveable between the first and second end position by means of said electrical coils. The electrical coils are arranged in an anti-series connection, and both coils are energized simultaneously for effectuating the movement of the armature between the two end positions. This technical solution provides a bistable actuating arrangement and two electrical coils are necessary therefore.

The document GB 1 ,454,354 discloses another magnetic actuator unit with only one electrical coil for moving the armature to one of the end positions. Additionally, an integrated opening spring is provided to generate force in the opposite direction. The opening spring is arranged inside the magnetic actuator unit surrounding the armature, which is also accommodated mostly inside the magnetic actuator unit in order to keep the volume of the arrangement as small as possible. However, the arrangement of the specific parts, especially the yoke surrounding the whole magnetic actuator unit, is not able to generate a high actuating force. For operation of modern medium voltage- circuit-breakers a higher force is required to operate the moving electrical contact.

Summary of the invention

It is an object of the present invention to provide a magnetic actuator unit for a circuit- breaker arrangement comprising a single electrical coil only which is combined with an opening spring in a compact design suitable for generating a high actuating force.

This object is achieved by the subject-matter of the independent claim 1. Further, exemplary embodiments are evident from the dependent claims.

According to the invention the opening spring of a magnetic actuator unit has a quite large diameter and is at least partly accommodated inside a groove formed in a discshaped armature whose dimension corresponds to the outer shape of the

ferromagnetic yoke. This means that for a circular disc-shaped armature the corresponding ferromagnetic yoke is also circular shaped having mainly the same diameter. In other words the invention proposes to host the opening spring in a groove inside the armature of a magnetic actuator unit.

Preferably, the groove is formed as an annular clearance having a U-shaped cross- section in order to provide enough space for accommodating the opening spring.

In a preferred embodiment, the annular grooves mainly or fully accommodate the opening spring means if the magnetic actuator unit is in the second end position. Thus, the opening spring rests mainly opposite to the electrical coil of the magnetic actuator unit in order to reduce the influence of the spring means and the groove on the force- generating ability of the magnetic circuit.

Depending on the specific application, the outer yoke of the magnetic actuator unit which mainly forms the outer dimensions of the magnetic actuator unit can be designed in various ways. For a circular cross-section of the yoke, the middle diameter of the annular groove preferably ranges between the inner and the outer diameter of the electrical coil. For a rectangular crossed section of the yoke, the middle diameter of the annular groove preferably lies outside said range between the inner and outer diameter of the electrical coil. In this case the reduction of the static holding fore of the magnetic actuator unit is mostly acceptable.

According to a preferred embodiment the at least one opening spring consists of a cylindrical compression spring of a quite high diameter made of spring wire steel, which is inserted in the annular groove. Alternatively, it is also possible to use several small cylindrical compression springs, which are inserted in the annular groove one to another in order to form a chain of adjacent single compression springs made of spring wire steel. According to another embodiment of the invention the opening spring can rest either directly on the bobbin of the electrical coil that will generally be made of plastic material, or alternatively, on an additional dedicated plate to avoid that the edges of the opening spring can scratch the bobbin of the electrical coil. Therefore, said dedicated plate is preferably made of a sheet metal material. ln order to reach a more compact design of the magnetic actuator unit it is

recommended to place the ring-shaped permanent magnet axially below the ring- shaped electrical coil, which is surrounded by the ferromagnetic cup-shaped yoke. On this arrangement an inner core element made of ferromagnetic material is surrounded by the permanent magnet.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment described hereinafter.

Brief description of the drawings

Below, the most preferred embodiment of the present invention is described in more detail with reference to the attached drawings.

Figure 1 shows a medium-voltage circuit-breaker arrangement with a magnetic actuator unit, and

Figure 2 shows a longitudinal view of a magnetic actuator unit in a first position,

Figure 3 shows a longitudinal view of a magnetic actuator unit in a second

position,

Figure 4 shows a longitudinal view of another magnetic actuator unit with different opening spring means.

All drawings are schematic.

Detailed description of the drawings

The medium-voltage circuit-breaker as shown in Figure 1 principally consist of a pole part 1 with an upper electrical terminal 2 and a lower electrical terminal 3 for electrically connecting a medium-voltage circuit. For the switching function, the lower electrical terminal 3 is connected to an electrical contact which is axially movable between the closed and the opened position via a jackshaft arrangement 4. This jackshaft arrangement 4 internally couples the mechanical energy of a magnetic actuator unit 5 to the pole part 1.

The magnetic actuator unit 5 consists of a - not shown - single electrical coil for switching of an armature 6 to the relative positions effected by magnetic fields.

The pole part 1 further comprises an external insulating sleeve 15 made of synthetic material for electrically insulating the pole part 1 to the environment. The insulating sleeve 15 supports and houses a vacuum interrupter insert 16 having the pair of corresponding electrical contacts as described above. Both electrical contacts are switchable inside the vacuum interrupter insert 8 under vacuum atmosphere.

According to Figure 2 the magnetic actuator unit is shown in the first end position according to the opened switching position of the connected - not shown - circuit- breaker.

The magnetic actuator unit uses a single electrical coil 7 for moving the armature 6 to a second position due to electrical current feed. Additionally to the single electrical coil 7 a permanent magnet 8 is provided which loads the armature 6 in the same direction. The single electrical coil 7 as well as the permanent magnet 8 is surrounded by an outer ferromagnetic yoke 9 for directing the magnetic flux to the movable ferromagnetic armature 6.

The ferromagnetic yoke 9 defines the outer geometrical dimensions of the magnetic actuator unit which has a circular cross-section according to the present example. In the axial direction the permanent magnet 8 is arranged below the electrical coil 7 in order to form a compact design. The ferromagnetic arrangement comprising the outer ferromagnetic yoke 9, the ring-shaped permanent magnetic 8 and the inner ferromagnetic core 10 direct the magnetic flux to the axial movable ferromagnetic armature 6. For permanent loading the armature 6 in the direction of the first position a single cylindrical compression spring 1 1 is provided. The cylindrical compression spring 1 1 is made of spring wire steel and mainly accommodated inside a corresponding annular groove 12. The annular groove 12 has a U-shaped cross-section and is formed as a kind of annular clearance. The diameter of the annular groove 12 is ranges between the inner and outer diameter of the electrical coil 7 as shown. Moreover, the discshaped armature 6 is adapted to the outer shape of the ferromagnetic yoke 9. On the front side of the electrical coil 7 the single compression spring 1 1 rests on a metal dedicated plate 13 covering a bobbin 14 of the electrical coil 7.

Figure 3 shows the magnetic actuator unit in the retracted state according to the second position in which the - not shown - pole part arrangement is in the closed switching position. In that position the single cylindrical compression spring 1 1 is fully compressed and fully accommodated inside the annular groove 12.

In the other embodiment according to Figure 4, instead of a single compression spring several small cylindrical compression springs 1 1a, 11 b (for example) are provided. These several cylindrical compression springs 11a, 1 1 b are also made of spring wire steel inserted in the annular groove 12'. For accommodating the cylindrical

compression springs 1 1a, 1 1 b, etc. the corresponding annular groove 11 ' has a larger cross-section than in the first embodiment as described above.

The invention is not limited by the preferred embodiments as described above which are presented as an example only but can be modified in various ways within the scope of protection defined by the following patent claims.

Reference signs

Pole part

upper electrical terminal

lower electrical terminal

jackshaft

magnetic actuator unit

armature

electrical coil

permanent magnet

ferromagnetic yoke

ferromagnetic core

compression spring

annular groove

dedicated plate

bobbin

insulating sleeve

vacuum interrupter insert