FIELD OF THE INVENTION

The present invention relates to three-position disconnector switch and a switchgear or control gear for low voltage, medium voltage or high voltage use with a substation.

BACKGROUND OF THE INVENTION

In state-of-art switchgear and control gear (also called controlgear) designs linear three-position disconnector switches are utilized, but they can suffer from too great a temperature rise.

There is a need to address this issue.

SUMMARY OF THE INVENTION

Therefore, it would be advantageous to have means to reduce overheating of a three- position switch for a switchgear or control gear.

The object of the present invention is solved with the subject matter of the independent claims, wherein further embodiments are incorporated in the dependent claims.

In a first aspect, there is provided a three-position disconnector switch, comprising:

an earthing contact;

a power out contact;

a power in contact;

a piston; and

a threaded rod. A length of the piston is such that in a first switch position an outer surface of a wall of the piston makes an electrical contact between the power out contact and the power in contact. The length of the piston is such that in a second switch position the outer surface of the wall of the piston does not make an electrical contact with either the earthing contact or the power in contact. The length of the piston is such that in a third switch position the outer surface of wall of the piston makes an electrical contact between the earthing contact and the power out contact. The piston comprises an inner threaded section configured to engage with the threaded rod. A length of the inner threaded section is less than the length of the piston. Rotation of the threaded rod is configured to engage with the inner threaded section to move the switch between the different switch positions.

In an example, the inner threaded section is configured not to rotate with respect to the threaded rod as the threaded rod rotates.

In an example, the piston comprises a second inner section adjacent to the inner threaded section. The second inner section is configured not to engage with the threaded rod.

In an example, the length of the piston comprises a length of the second inner section added to the length of the inner threaded section.

In an example, a diameter of an inner cross section of the second inner section is substantially larger than a diameter of a cross section of the threaded rod.

In an example, an internal surface of the second inner section has a surface area greater than that of a smooth cylinder of the same length and internal diameter.

In an example, the internal surface of the second inner section is one of: threaded or has ridges extending in an axial direction.

In an example, a material is added to the inside of the second inner section to provide a surface area greater than that of a smooth cylinder of the same length and internal diameter. ln an example, the added material is one of: a tube, a sheet, and expanded metal or mesh, a corrugated sheet, an insulation material with high heat emissivity; a thermally conductive material.

In an example, an outer surface of the piston has a surface area greater than that of a smooth cylinder of the same length and external diameter.

In an example, the outer surface of the piston one of: threaded or has ridges extending in an axial direction.

In an example, the wall of the piston comprises one or more holes extending in a substantially radial direction. The piston is configured such that air can flow into the piston in an axial direction and flow out of the one or more holes, or configured such that air can flow into the piston through the one or more holes and out in an axial direction.

In an example, the earthing contact comprises one or more holes extending through an outer wall of the earthing contact in a substantially radial direction.

In an example, the power out contact comprises one or more holes extending through an outer wall of the power out contact in a substantially radial direction.

In an example, the power out and/or power in contact comprises one or more holes extending through an outer wall of the power in contact a substantially radial direction.

In a second aspect, there is provided a low voltage, medium voltage of high voltage switchgear or control gear comprising one or more three-position disconnector switches according to the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be described in the following with reference to the following drawings: Fig. 1 shows a schematic representation of cross-sections through a conventional design of linear three-position disconnector switch;

Fig. 2 shows a schematic representation of a cross-section through an example of the new design of linear three-position disconnector switch;

Fig. 3 shows a schematic representation of examples of the piston with increased surface area of the new design of linear three-position disconnector switch;

Fig. 4 shows schematic representation of an example of the power out contact of the new design of linear three-position disconnector switch; and

Fig. 5 shows a schematic example of the power out contact and the piston of the new design of linear three-position disconnector switch.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows an example of a conventional design of three-position disconnector switch Used in medium voltage applications, that has linear movement of components.

In Fig. 1 the following components are shown:

1 : earthing contact housing,

2: power outgoing contact housing,

3: power incoming contact housing,

4: tube/piston housing arranged for conductive connection of required contacts, and 5: motor operated threaded rod which is used to move and hold the piston in a desired position.

However, the design is relatively large size and there is an inability easily to dissipate the heat during operation and the temperature rise testing, with heat transfer primarily occurring by radiation to the surrounding environment.

The new design of three-position disconnector switch addresses these problems. It is smaller, and air flow inside of the parts carrying high current is enabled to provide cooling.

Figs. 2-5 relate to the new design of three-position disconnector switch. In an example, the three-position disconnector switch comprises an earthing contact 1 , a power out contact 2, a power in contact 3, a piston 4, and a threaded rod 5. A length of the piston is such that in a first switch position an outer surface of a wall of the piston makes an electrical contact between the power out contact and the power in contact. The length of the piston is such that in a second switch position the outer surface of the wall of the piston does not make an electrical contact with either the earthing contact or the power in contact. The length of the piston is such that in a third switch position the outer surface of wall of the piston makes an electrical contact between the earthing contact and the power out contact. The piston comprises an inner threaded section 7 configured to engage with the threaded rod. A length of the inner threaded section is less than the length of the piston. Rotation of the threaded rod is configured to engage with the inner threaded section to move the switch between the different switch positions. This rotation can be provided by an appropriate motor.

In an example, the inner threaded section 7 is configured not to rotate with respect to the threaded rod as the threaded rod rotates.

In this way, as the threaded rod rotates, the inner threaded section 7 of the piston, which is connected to the main body of the piston, is moved up and down the threaded rod and moves the piston to its different switch positions depending on the direction of rotation of the threaded rod.

In an example, the inner threaded section 7 of the piston is fixedly connected to the main body of the piston.

In an example, the inner threaded section 7 is a nut fixed within a main body of the piston.

In an example, in the second position the outer surface of the wall of the piston makes an electrical contact with the power out contact.

According to an example, the piston comprises a second inner section adjacent to the inner threaded section. The second inner section is configured not to engage with the threaded rod.

According to an example, the length of the piston comprises a length of the second inner section added to the length of the inner threaded section. According to an example, a diameter of an inner cross section of the second inner section is substantially larger than a diameter of a cross section of the threaded rod.

According to an example, an internal surface of the second inner section has a surface area greater than that of a smooth cylinder of the same length and internal diameter.

According to an example, the internal surface of the second inner section is one of: threaded or has ridges extending in an axial direction.

According to an example, a material is added to the inside of the second inner section to provide a surface area greater than that of a smooth cylinder of the same length and internal diameter.

According to an example, the added material is one of: a tube, a sheet, and expanded metal or mesh, a corrugated sheet, an insulation material with high heat emissivity; a thermally conductive material.

According to an example, an outer surface of the piston has a surface area greater than that of a smooth cylinder of the same length and external diameter.

According to an example, the outer surface of the piston one of: threaded or has ridges extending in an axial direction.

According to an example, the wall of the piston comprises one or more holes extending in a substantially radial direction, and wherein the piston is configured such that air can flow into the piston in an axial direction and flow out of the one or more holes, or such that air can flow into the piston through the one or more holes and out in an axial direction.

According to an example, the earthing contact comprises one or more holes extending through an outer wall of the earthing contact in a substantially radial direction.

According to an example, the power out contact comprises one or more holes extending through an outer wall of the power out contact in a substantially radial direction. According to an example, the power out and/or power in contact comprises one or more holes extending through an outer wall of the power contact in a substantially radial direction.

One or more three-position disconnector switches as described above can be used in A low voltage, medium voltage of high voltage switchgear or control gear.

In this way, improvement of the temperature distribution in a three-position

disconnector switch is provided. Improved cooling is achieved by a hollow design of piston, with additional holes and increased inner/outer surface area of the piston. Further enhancements of the cooling effect is possible by allowing air flow in the power contact areas.

Continuing with Figs. 2-5, as shown in Fig. 2 a smaller design of three-position disconnector switch is provided with an improvement of its temperature distribution. Improved cooling is achieved by a hollow design of piston together with hollow power contacts.

Referring to Fig. 2, this shows a hollow design with a power incoming contact 3, an opening in the front of the piston 4 and where there are additional holes 6 in the piston 4. A threaded rod is configured to moving through rotation within the nut 7, that is connected to the piston 4 in a way that the piston is moved back and forth without its own rotation. Thus, the nut 7 is pulled up and down the threaded rod as it rotates and in doing so moves the piston to different switching positions of the three-position disconnector switch. This design leads to an air 10 flowing through the piston 4 and thus significantly providing for an improved cooling effect. Such cooling can improve cooling of all parts which are in contact or in the vicinity of the piston. This cooling effect can be further improved by enlarging the inner surface area of the piston, or also the enlarging its outer surface area. Examples of the inner surface side cross-section are shown in Fig. 3.

Fig. 3 at a) there is shown an enlarged piston surface area, for example by forming, at b) there is shown an enlarged piston surface area achieved through a thread being machined inside the piston, where this thread is different to the thread that the threaded rod engages and this part of the piston has a wider internal cross-section than that of the nut. Fig. 3 at c) shows examples of additional material inserted within the piston interior. All of the examples of Fig. 3 provide for an increased surface area that leads to an improved cooling effect.

The Inner surface area shown at Fig.3a) could be done for example by cold forming. Machining can be employed to provide the thread (Fig. 3b) inside the piston. Additional material can be inserted inside the piston area (Fig. 3c), where such material can be for example a tube, a sheet or expanded metal or mesh, or even the corrugated sheet or insulation material with high heat emissivity. Material of this additional part can be any kind of thermally conductive material.

Further enhancement of the cooling effect in the power outgoing contact 2 or power incoming contact 3 can also be provided through the utilization of air flow. This is enabled by using a multilamella contact providing a circular hollow space in the contact area, and additional holes in the contact, which directs the air from the bottom to the top. This is shown in Fig. 4, where a simplified 3D model of one of the contacts is shown and a cross section view is also shown. This cooling embodiment can be applied to all of the contact types. Fig. 5 then shows the piston with one of the contacts, as discussed above.