Electrical switching device

Technical Field

The invention relates to an electrical switching device comprising a longitudinal enclosure filled with an insulating gas for forming an interrupting chamber having a longitudinal axis, whereby the enclosure comprises an arcing volume, two arcing contacts, a blown device for blowing the insulating gas to the arcing volume to extinguish an arc generated during breaking operations by electrical arcing between the two arcing contacts and an exhaust volume connected to the arcing volume for cooling hot gases generated during the breaking operations.

Background Art

In an electric power system, an electrical switching device is typically provided as a circuit breaker used to control, protect and isolate electrical equipment. Such electrical switching device is used both to de-energize equipment to allow work to be done and to clear faults downstream. Gas-insulated switchgear, GIS, is a form of the electrical switching device where conductors and contacts are insulated by pressurized insulating gas, mainly sulfur hexafluoride gas, SF6, within a tank.

For environmental reason alternative insulation gases are under development to replace SF6, such as example CO2 and admixtures. However, for such alternative insulation gases improved insulating gas cooling concepts compared to SF6 are required for keeping an exhaust and tank volumes of such electrical switching device sufficiently small.

Summary of invention It is therefore an object of the invention to provide electrical switching device characterized by an improved insulating gas cooling concept in particular for alternative insulation gases such as for example CO2.

The object of the invention is solved by the features of the independent claims. Preferred implementations are detailed in the dependent claims.

Thus, the object is solved by an electrical switching device comprising a longitudinal enclosure filled with an insulating gas for forming an interrupting chamber having a longitudinal axis, whereby the enclosure comprises an arcing volume, two arcing contacts, a blown device for blowing the insulating gas to the arcing volume to extinguish an arc generated during breaking operations by electrical arcing between the two arcing contacts and an exhaust volume connected to the arcing volume for cooling hot gases generated during the breaking operations, and the exhaust volume comprises an array of distantly positioned and additively manufactured cooling rods, which are arranged within the exhaust volume perpendicular to a gas flow of the hot gases and/or extend radial in respect to the axis.

A key point of the invention constitutes the array of distantly positioned and additively manufactured cooling rods, provided as in particular perpendicular elements arranged in the hot gas flow. Exhaust gas cooling is very crucial for CO2 and admixtures such as for example 02 and C4-FN, since gas temperatures will be significantly higher than for SF6. In SF6 hot gases typically stay below 2000 K, while CO2 mixtures can easily exceed 3000 K due to thermodynamic properties of the gases.

For dielectric interruption performance in the enclosure, i.e. insulation to ground, very low breakdown voltages result at temperatures above 2500 K. The proposed solution advantageously allows limiting exhaust temperatures to below 2500 K or even below 2000 K. Such temperature decrease is achieved as with the proposed array of rods sufficient surface area is offered to the hot gases. With the proposed solution, an exemplary impinged surface area of the rods with 0.08 to 0.2 m2 corresponds to a transferred energy of roughly to 70 to 140 kJ for CO2. The hot gas will impinge on a front of each rod leading to locally enhanced heat transfer coefficient, a so-called impinging jet.

Further, the proposed array of distantly positioned and additively manufactured cooling rods in the exhaust volume allows for keeping a similar enclosure size as with SF6 electrical switching devices, such as circuit breakers, known from prior art. Thus, the proposed solution reduces costs and enables use of similar bay width as for SF6 electrical switching devices i.e. at similar cost.

While the rods are additively manufactured i.e. 3D printed, the rods may possibly manufactured by other methods like casting, a kind of disc or wheel, soldering etc. With additively manufacturing a design of the array can possibly be manufactured as one piece with minimum need of post-processing. The exhaust volume may comprise several arrays, for example provided as discs or pieces, which can be placed in series for increasing a total surface area.

The electrical switching device is preferably provided as circuit breaker or more generally as gas-insulated switchgear, GIS, alternative as disconnector of the like. The electrical switching device is preferably configured for operating in a medium voltage regime of 10 kV to 100 kV and/or in a high voltage regime of 100 kV to 1200 kV. The electrical switching device is preferably provided as a high voltage device, whereby the term high voltage relates to voltages that exceeds 1 kV.

A high voltage preferably concerns nominal voltages in the range from above 72 kV to 800 kV, like 145 kV, 170 kV, 245 kV or 420 kV. The enclosure is preferably provided with two closed ends forming a so-called tank. The insulating gas is preferably provided as CO2, 02 or C4-FN, may it be gaseous and/or liquid, and in particular can be a dielectric insulation gas or arc quenching gas.

The two arcing contacts are preferably provided as pin and tulip contacts, whereby at least one of the arcing contacts, preferably both arcing contacts are provided movable along the longitudinal axis for providing an electrical connection with the other arcing contact. The blown device is preferably provided as nozzle, in particular as insulating nozzle. The exhaust volume is preferably fluidly connected to the arcing volume. The rods are preferably arranged such that hot gases imping a surface thereof. Additively manufactured, also referred to as 3D-printing, means preferably that the array of rods is constructed from of a three-dimensional object for example from a CAD model or a digital 3D model, whereby material is deposited, joined or solidified under computer control to create the array with the rods as three-dimensional object, with the material being added together, typically layer by layer.

According to a preferred implementation, the rods are radially oriented in respect to the axis and/or are arranged equidistant. Preferably, the rods are arranged essentially radially and/or arranged within a flow of the hot gases. The array may comprise a number of rods arranged axially behind each other, preferably radially offset between the rows. The array may comprise a tube-like shape extending along the longitudinal axis having a tube-like longitudinally extending core and an outer distantly thereto arranged longitudinally extending tube-like frame, whereby the rods extend between the core and the frame. Such way the hot gases preferably flow axially between the core and the frame.

In a further preferred implementation, the rods are provided as fins or fin-like and/or comprise a varying cross section over their length. An outer shape of the rods is preferably optimized for flow i.e. low pressure losses, for example having no sharp edges or the like. Preferably the cross section increases radially away from the axis, for thereby increasing a flow area. The cross-section may increase in radial direction away from the longitudinal axis, for example by 10, 20, 30 or 50% from an inner end to an outer and foremost away from the longitudinal axis.

According to another preferred implementation, a number of rods increase radially in respect to the axis and/or whereby the rods comprise a Y-shape or a higher order Y-shape, whereby the Y-shape in particular extends axially. With evenly distributed flow areas over the radius a pressure drop can be minimized, in particular when having a radially increasing number of rods. The Y-shape rods may extends axially and/or radially, in particular in a two-dimensional or three-dimensional manner. A higher order Y-shape may comprise a combination of various Ys i.e. that upper ends of the Y are each connected with a lower end of another Y. In a further preferred implementation, the rods extend circumferentially around the axis. Such wise rods may extend from the inner core circumferentially around the axis in radial direction towards the outer frame. Preferably, the rods extend completely i.e. by 360° around the axis.

According to a further preferred implementation, the rods comprise additively manufactured stainless steel, titanium or ceramics, or other possible materials. Preferably, the rods comprise a high heat conduction coefficient, bearing the advantage that a small amount of ablated material in a hot gas jet would not add electrically conductive metal vapor to the hot gases. Besides that other materials are possible which provides respective heat resistance.

In another preferred implementation, the rods comprise a surface structure having a corrugation and/or microstructure. Such measures can be used for optimizing heat transfer respectively cooling of the hot gases. Preferably, the surface structure leads to a heat transfer coefficient of more than 10 kW/m2K

According to a further preferred implementation, the rods together comprise an outer surface area of > 0,1 m ² and < 2 m ² , > 0,2 m ² and < 1 m ² , in particular 0,3 m ² , and/or the rods each comprise a radius of > 0,1 mm and < 2 cm. Thickness of the rods is an important aspect, as it needs to be thick enough for avoiding evaporation of the rods and for ensuring efficient heat transfer over a time of interest of for example 20 to 30 ms. Thus, a diameter of the rods is preferably greater than 2 or 10 mm, typically.

In another preferred implementation, each rod comprises a length > 5 mm and < 10 cm, and/or the array comprises > 100 and < 1000 rods, in particular > 100 and < 600 rods. The array may comprise various layers of rods arranged axially behind each other. Each layer preferably circumferentially extends around the axis.

The object of the invention is further solved by a circuit breaker comprising the electrical switching device as described before. So-called protection devices, typically circuit breakers, are basically suitable for carrying, for a specified time, and breaking currents under specified abnormal circuit conditions, namely short circuits. Alternatively, the electrical switching device is provided as contactor. So called maneuvering switching devices, such as contactors, are capable of making, carrying and breaking currents under normal circuit conditions including overload conditions. Such contactors are widely used for example to switch on/off electric motors, are required to satisfy a number of conditions which are important to guarantee the proper functional performances during their service life in electrical networks.

The object of the invention is even further solved by a method for manufacturing an array of cooling rods for an electrical switching device comprising a longitudinal enclosure filled with an insulating gas for forming an interrupting chamber having a longitudinal axis, whereby the enclosure comprises an arcing volume, two arcing contacts, a blown device for blowing the insulating gas to the arcing volume to extinguish an arc generated during breaking operations by electrical arcing between the two arcing contacts and an exhaust volume connected to the arcing volume for cooling hot gases generated during the breaking operations, comprising the step of: additively manufacturing the array of distantly positioned cooling rods to be arranged within the exhaust volume perpendicular to a gas flow of the hot gases and/or extend radial in respect to the axis.

Additive manufacturing allows for producing the array in a very cost-effective manner, which otherwise would be very difficult to produce in a competitive manner. Further, the proposed array allows for effectively cooling the hot gases.

According to a preferred implementation, the method comprises the step of: additively manufacturing the rods as fins or fin-like and/or having a varying cross section over their length.

In another preferred implementation, the method comprises the step of: additively manufacturing the array having a number of rods increasing radially in respect to the axis and/or additively manufacturing the rods comprising a Y-shape or a higher order Y- shape, whereby the Y-shape in particular extends axially. According to a further preferred implementation, the rods extend circumferentially around the axis.

In another preferred implementation, the method comprises the step of: additively manufacturing the array of distantly positioned cooling rods by using stainless steel, titanium or ceramics.

Further implementations and advantages of the method are directly and unambiguously derived by the person skilled in the art from the electrical switching device as described before.

Brief description of drawings

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

In the drawings:

Fig. 1 shows a gas-insulated switchgear, GIS, as an electrical switching device having array of rods according to a preferred implementation in a sectional view, and

Fig. 2 shows to the left the array in a perspective view and to the right the array in a side view according to the preferred implementation.

Description of implementations

Fig. 1 shows a gas-insulated switchgear, GIS, as an electrical switching device according to a preferred implementation in a sectional view.

The electrical switching device comprises a longitudinal tube-like enclosure 1 having a diameter of around 0.5 to 1 m, typically, which is filling with an insulating gas such as C02, thereby defining an interrupting chamber 2 having a longitudinal axis 3. The enclosure 1 comprises an arcing volume 4, extending along the axis 3, wherein which two arcing contacts 5 are arranged. The two arcing contacts 5 are movable along the longitudinal axis 3. The enclosure 1 further comprises a blown device 6 such as an insulating nozzle for blowing the insulating gas to the arcing volume 4, for such wise extinguishing an arc generated during breaking operations by electrical arcing between the two arcing contacts 5.

Hot gases generated during such breaking operations are cooled in an exhaust volume 7, which is fluidly connected to the arcing volume 4. Therefore, the arcing volume 4 transitions on both longitudinal ends into the exhaust volume 7, which such wise longitudinally extends in vicinity to both arcing contacts 5. In particular, in respect to the left side of Fig. 1 , the respective exhaust volume 7 extends coaxially around the longitudinal axis 3, having an inner exhaust volume 7 being passed by the hot gases first followed by a coaxially thereto arranged outer exhaust volume 7 flown through by the hot gases second. In respect to the right side of Fig. 1 , the exhaust volume 7 comprises two axially arranged areas being passed one after the other by the hot gases.

At least one, presently each of the two axially opposite arranged exhaust volumes 7 comprises at least one array 8 with distantly positioned cooling rods 9, shown in more detail in Fig. 2. Specifically, Fig. 2 shows to the left the array 8 in a perspective view, while Fig. 2 shows to the right the array 8 in a side view. Turning back to Fig. 1 , said figure shows at least four different locations, where said arrays 8 can be positioned. On the left side in Fig. 1 , both the outer and inner exhaust volume 7 may comprise one array 8 circumferentially extending around the longitudinal axis 3. On the right side in Fig. 1 , the two axially arranged areas of the exhaust volume 7 may each comprise one array 8 arranged such wise distant from each other.

As explained, the array 8 comprises a plurality of with distantly positioned cooling rods 9, which are arranged within the exhaust volume 7 perpendicular to a gas flow direction of the hot gases i.e. extend radially away from the longitudinal axis 3. Such wise the cooling rods 9 stand in the hot gas flow, which impinges on a front of each rod 9 leading to locally enhanced heat transfer coefficient i.e. an impinging jet. Thereby the heat transfer coefficient depends on a shape of the rods 9, which can be provided as fins, fin-like or having a round diameter.

The array 8 comprises some 100 rods 9, for example 600 rods of 2 mm radius and/or 4 mm radius, thereby having a fill factor of below 0,5 for a typical axial length of 0.1 m. The rods 9 can be arranged in sets axially behind each other. With a total surface area calculated based on a length per rod 9 of 4 cm and for the before estimated number of rods 9 this yields a surface area of about 0.3 to 0.6 m2, in addition to other possibly existing outer exhaust areas. Such wise an energy transfer, while assuming heat transfer coefficients 6 to 14 kW/(m ^A 2K), Tav = 3000 K and t=10 ms, of roughly 50 to 250 kJ can be achieved. Generally, 150 kJ can be achieved for each exhaust on average.

The rods 9 are additively manufactured by using stainless steel, titanium or ceramics, such allowing a cost effective manufacturing while providing sufficient heat resistance respective cooling capability. As can be seen from Fig. 3, the rods 9 are radially oriented in respect to the axis 3 and are arranged equidistant in multiple rows axially distant from each other. The rods 9 may comprise a varying cross section over their length. The cross-section may comprise a diameter that increases in radial direction away from the axis 3.

In Fig. 2 the rods 9 extend from an inner tube-like shaped core 10, which extends along the axis 9, towards an outer distantly thereto arranged longitudinally extending tube-like frame 11 . Such way the rods 9 extend in axial direction between the core 10 and the frame 11 so that the hot gases flow axially between the core 10 and the frame 11 away from the arcing contacts 5. While the array 8 shown to the left in Fig. 2 comprises Y-shaped rods 9 i.e. a number of rods 9 that increase radially in respect to the axis 3, the array 8 shown to the right in Fig. 2 comprises higher order Y- shaped rods 9. From an initial Y-shaped rods 9 connected to the core 10 two further Y-shaped rods 9 are connected, which are subsequently extend towards the frame 11 . Thereby the rods 9 extend circumferentially around the axis 3.

With such configuration of rods 9 an outer surface area of all rods 9 of > 0,1 m ² and < 2 m ² , > 0,2 m ² and < 1 m ² , in particular 0,3 m ² can be achieved when having rods 9 with a radius of > 1 mm and < 2 cm each. Thereby, the rods 9 may each comprises a length > 1 cm and < 10 cm, while each array 8 may comprise > 100 and < 2000 rods, in particular ^ 100 and < 600 rods 9. For further improving the cooling capability of the array 8 the rods may comprise a surface structure having a corrugation and/or microstructure.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed implementations. Other variations to be disclosed implementations can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

Reference signs list

1 enclosure

2 interrupting chamber

3 longitudinal axis

4 arcing volume

5 arcing contact

6 blown device

7 exhaust volume

8 array

9 cooling rod