EP4586296A1

EP4586296A1 - Heat exchanger with lattice structure for a medium or high voltage circuit breaker

Info

Publication number: EP4586296A1
Application number: EP24151392.8A
Authority: EP
Inventors: Ludovic DARLES; Cyril Gregoire; Philippe Manin
Original assignee: General Electric Technology GmbH
Current assignee: Ge Vernova Technology GmbH
Priority date: 2024-01-11
Filing date: 2024-01-11
Publication date: 2025-07-16

Abstract

The invention concerns a medium or high voltage circuit breaker (20, 22) comprising a casing extending along an axis XX', a pair of arcing contacts, of which at least one of them is movable, an exhaust path (14, 16) for gases resulting from the separation of said arcing contacts, said exhaust path (14, 16) comprising at least one cooling device (10) for a circuit breaker GIS comprising a 3 dimensional lattice of beams.

Description

TECHNICAL FIELD AND PRIOR ART

The invention relates to the field of medium or high-voltage gas circuit-breakers. Such circuit-breakers can be part of a metal-clad substation or air insulated switchgear.
The invention relates more particularly to a heat exchanger and to a method of cooling hot gases generated by the breaking that is performed by such a circuit-breaker, and to the associated circuit-breaker structure.
A typical High-voltage (HV) circuit breaker is known from FR 2946181 , comprising baffles to remove hot gases after an opening of the contacts.
Such circuit breakers are too bulky and another solution is needed to reduce the size of a circuit breaker.

SUMMARY OF THE INVENTION

The invention first concerns a cooling device for a circuit breaker, for example for a medium or high voltage circuit breaker, comprising a 3 dimensional lattice of beams and holes or cells.
Hot gas, for example generated by an opening of a circuit breaker, can swirl and/or meander through a lattice of a cooling device according to the invention, thereby flowing along a large heat exchange surface of the many branches of the lattice. The hot gas is thus cooled. The cooling can also result from mixing in the lattice between cold and hot gas.
The cooling effect obtained by a device according to the invention contributes to the reduction of the size of a circuit breaker in which it is implemented : indeed cold gas have a better dielectric properties than hot gas; therefore, improving or optimizing the mixing and cooling allows a reduction of the overall dimension of the device.
Said beams can preferably be made of aluminium and/or steel and/or copper and/or any other suitable composite or metallic material
One or more beam(s) can have a width comprised between 4 mm and 20 mm.
One or more beam(s) can have a round cross-section (circular or without sharp edge).
In an embodiment, said lattice has a total length of between 5 cm to 40 cm and/or an external diameter comprised between 5 cm and 50 cm and/or an internal diameter comprised between 0 and 40 cm.
The invention also concerns a circuit breaker comprising a casing extending along an axis XX', a pair of arcing contacts and at least one cooling device according to the invention.
Said pair of arcing contacts can comprise :

a stationary contact;
at least one moving contact, mounted or arranged to move in translation along said axis XX';
or 2 moving contacts, mounted or arranged to move in translation along said axis XX'.

A circuit breaker according to the invention can further comprise gas exhaust baffles to remove hot gas generated by an opening of said pair of arcing contacts. At least one cooling device according to the invention can be located on the path of said hot gas through or along said gas exhaust baffles.
The casing can be filled with a gas comprising SF₆, and/or CO₂, and/or O₂ or a mixture of these gas. It can also comprise heptafluoroisobutyronitrile (CAS no 42532-60-5) and/or heptafluoroisopropyl trifluoromethyl ketone (also named 2-butanone, 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)- (CAS No 756-12-7)) and/or CO₂ and/or O₂ and/or N₂ and/or an oxygenated compounds, for example said comprising both CO₂ and a fluorinated compound, for example heptafluoroisobutyronitrile and/or heptafluoroisopropyl trifluoromethyl ketone.
The invention also concerns a method for opening a circuit breaker according to the invention, comprising:

separating the contacts of the circuit breaker, thereby generating hot gas;
flowing at least part of said hot gas through said cooling device.

Said hot gas can be at a temperature of several thousand K and/or can have a speed between 1 m/s and 400 m/s at the lattice inlet.
Said hot gas can be at a temperature between 1500 K and 7000 K at the lattice inlet and /or have a speed between 1 and 400m/s at the lattice inlet.
The invention also concerns a method for making a cooling and mixing device according to the invention, comprising metal casting or 3D printing said device.

BRIEF DESCRIPTION OF THE DRAWINGS

figures 1 shows an example of a cooling device according to an embodiment of the invention, comprising a lattice structure;
figure 2 shows a simulation of the cooling effect of a cooling device according to an embodiment of the invention and a 2D simulation of the circulation of a gas through said cooling device;
figure 3A illustrates a circuit breaker provided with a cooling device according to an embodiment of the invention;
figure 3B illustrates a circuit breaker provided with a cooling device according to an embodiment of the invention, located at another location than on figure 4A;
figure 4 shows another portion of a circuit breaker provided without a cooling device according to an embodiment of the invention.
figures 5A and 5B show examples of an octet truss which can be implemented in a cooling device according to the invention;
figures 6A and 6B show examples of Kelvin cells.

DETAILLED DESCRIPTION OF SPECIFIC EMBODIMENTS

An example of a heat exchanger (or cooling device) 10 according to an embodiment of the invention is illustrated on figure 1.
It comprises a 3 dimensional lattice made for example of aluminium and/or steel and/or copper and/or any other suitable material through which hot gas (at a temperature of several thousand K, for example between 3000 K and 7000 K) can circulate, following a tortuous path and exchanging heat with the beams of the lattice and favouring mixing of hot gas with cold gas present in the lattice.
The 3D lattice may have for example a total length L (measured along an axis Y, see figure 1) of about 5 cm to 40 cm and/or an outer diameter (measured in a plane XZ perpendicular to the axis Y) comprised between 5 cm and 50 cm and/or an inner diameter comprised between 0 and 40 cm (in other words, the lattice may surround a central cylinder which is free of any solid material, said cylinder having said inner diameter comprised between 0 and 40 cm).
The 3D lattice of a heat exchanger (or cooling device) 10 according to an embodiment of the invention can be implemented at various locations in a circuit breaker on any path of hot gases generated by a breaking operation and has a cooling effect.
Figure 2 shows a simulation of a gas flow through a lattice according to the invention, whereby the gas at the lattice inlet has a temperature of 4000 K (during a short time interval of about 10 ms to 50 ms), at a speed of 30 m/s, and a temperature of 3854 K (at a speed of 25.2 m/s) at the lattice outlet. The lattice thus has a cooling effect. It also shows a sectional view of a 2D simulation, showing the complex path followed by the gas through the lattice. The gas swirls and/or meanders through the lattice, thereby flowing along a large heat exchange surface of the many branches of the lattice.
The 3D lattice has branches or beams which can be for example cylindrical and which have a size or width (cross-section or larger dimension or diameter in a plane perpendicular to the extension length of the beam) comprised for example between 4 mm and 20 mm for an optimal cooling effect (a size less than 4 mm cannot sustain temperatures of several thousand K and a size larger than 20 mm reduces the number of possible cells). It can be formed by a 3D unit cell, for example Kelvin cells (a Kelvin cell consists of six flat quadrilateral and eight hexagonal faces, which have some curvature). It can be packed to fill all space, in a body-centred cubic arrangement) or octet truss (illustrated on figures 5A and 5B) repeated in the 3 dimensions of the space.
A Kelvin cell (illustrated on figures 6A and 6B), i.e. so-called tetrakaidecahedron in some publications, has fourteen faces (eight hexagonal and six quadrilateral) and twenty-four vertices; reference is also made to US 2986241 .
In an octet-truss as defined by US 2986241 , the main structural elements (e.g. struts or triangular sheet members) form equilateral triangles interconnected in a pattern consisting of octahedrons and tetrahedrons with the major axes of all octahedrons in parallelism throughout the framework. Thus all such structural elements are comprised within a single octahedron-tetrahedron system, and this apparently yields a new optimum of the intersecting truss surfaces which holds to the integrity of the strength-creating octatetra system.
Preferably, the ratio S/V, where S is the total surface of the beams of the lattice and V its volume is maximum, it is for example comprised between 500 and 2000m²/m³.
The porosity of the lattice (the ratio between the volume of gas inside the lattice over the volume of the beams) can be comprised between 50 and 95%: a porosity below 50% may induce a too large pressure drop blocking the gas flow; a porosity above 95% will result in a low efficiency of the mixing and cooling.
Preferably the lattice is made by a casting method or 3D printing. For the casting method, the lattice will be casted (metal pouring in to mould) with the use of a mould that will be preferably 3D printed. The advantage of this method is its low cost .Alternatively, the lattice can be 3D-printed with additive printing method which allows even further possibilities for shapes and complexity of the lattice. It can be done in a variety of processes in which material is deposited, joined or solidified under computer control, with the material being added together (such as wire or powder grains being fused), typically layer by layer.
The gas are generated by a breaking operation of circuit breaker, for example as disclosed in FR2946181 or in in US2007/158310 .
Figure 3A schematically shows a circuit breaker 20, having for example the structure disclosed in US2007/158310 , provided with a lattice 10 according to the invention in an area 12 called exhaust where hot gases resulting from a breaking process are flowing (the flow of hot gas being shown by an arrow 14). The lattice is preferably located away from the arcing area to avoid direct exposure to plasma radiation. It is therefore preferably located in the casing called exhaust. It can be used or not in combination with baffle(s) or meanders as existing in the prior art.
Figure 3B is another example of a zone 16 of a circuit breaker 20 where a lattice 10 according to the invention can be located to cool the hot gases generated by a breaking operation, the path of the hot gases being represented by arrow 14: in this example, the circuit breaker is provided with gas exhaust baffles 26 which guide the hot gas.
The details of a circuit breaker are not represented on figures 3A and 3B. More details are given for example in FR2946181 or in US2007/158310 .
A cooling device according to the present invention can be implemented at least 4 types of circuit breakers : a Dead Tank type, a Live Tank type, a Gas insulated switchgear (GIS) or a Generator circuit breaker (GCB).
Usually, a circuit-breaker has a pair of arcing contacts:

a stationary contact which can be fastened to a casing and a moving contact, mounted or arranged to move in translation along an axis XX' (see figures 3A and 3B); said moving contact can be secured to an insulating nozzle that is designed to blow hot gases that are generated on separation of the contacts;
or 2 moving contacts, mounted or arranged to move in translation along an axis XX' (see figures 3A and 3B); one of said moving contact can be secured to an insulating nozzle that is designed to blow hot gases that are generated on separation of the contacts.

A circuit-breaker also has a pair of main contacts, at least one of them being movable along said axis XX'. During the breaking procedure, said main contacts open first, and then the arcing contacts.
An actuating system for opening the circuit-breaker comprises for example a rod actuated at one of its ends by a lever 8 mounted to pivot about an axis.
During the opening procedure of the circuit-breaker, said two arcing contacts separate, for example at a speed between 1 m/s and 20 m/s. At a predetermined distance d between them (which can be at a few cm, for example between 2 mm and 300 mm), an arc is formed, with a current of up to several Thousands of A, for example between 1 A and 300 kA.
The hot gases generated by the opening of the contacts can follow a route defined by the baffles as explained in FR 2946181 or in US2007/158310 . A cooling device according to the invention can be located on the path of the gas through said baffles, as shown on figures 3A and 3B.
Figure 4 shows a circuit breaker 20 without a lattice according to the invention, the hot gas successively flowing through the zones 15 and 16.
Figures 3A and 3B are only examples of a circuit breaker according to the invention: a lattice according to the invention can be located at any other place in the circuit breaker or at its outlet, on the path of the flow of hot gas.
A circuit breaker according to the invention comprises and operates in a gas, for example SF₆; alternatively, in order to reduce the greenhouse effects resulting from the use of SF₆, the following gas may be used:

a gas comprising heptafluoroisobutyronitrile and/or heptafluoroisopropyl trifluoromethyl ketone (also named 2-butanone, 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)- (CAS No 756-12-7)), possibly mixed with a gas or a dilution gas comprising at least CO₂ and/O₂ and/or N₂ and/or and/or an oxygenated compound;
or in a gas comprising at least SF₆, and/or CO₂ and/O₂ and/or N₂ and/or an oxygenated compound.

For example said gas can comprise both CO₂ and a fluorinated compound, for example heptafluoroisobutyronitrile and/or heptafluoroisopropyl trifluoromethyl ketone.
The invention can for example find application in circuit breakers which operate under a very high rated voltage (for example between 10 kV and 1200 kV).

Claims

A medium or high voltage circuit breaker (20, 22) comprising a casing extending along an axis XX', a pair of arcing contacts, of which at least one of them is movable, an exhaust path (14, 16) for gases resulting from the separation of said arcing contacts, said exhaust path (14, 16) comprising at least one cooling device (10) comprising a 3 dimensional lattice of beams and cells.
A medium or high voltage circuit breaker (20, 22) according to claim 1, said beams of said cooling device (10) being made of aluminium and/or steel and/or copper.
A medium or high voltage circuit breaker (20, 22) according to claim 1 or claim 2, said beams having a width comprised between 4 mm and 20 mm and rounded edges
A medium or high voltage circuit breaker (20, 22) according to any of claims 1 to 3, wherein:
- the ratio S/V, where S is the total surface of the beams of the lattice and V its volume is maximum is comprised between 500 and 2000 m²/m³;

- and/or the porosity of said lattice being comprised between 50 and 95%
A medium or high voltage circuit breaker (20, 22) according to any of claims 1 to 4, said lattice having at least one of :
- a total length (L) of between 5 cm to 40 cm;

- an external diameter (D) comprised between 5 cm and 50 cm;

- an internal diameter less than 40 cm;
A medium or high voltage circuit breaker according to any of claims 1 to 5, said pair of arcing contacts comprising :
- a stationary contact and a moving contact, mounted or arranged to move in translation along said axis XX';

- or 2 moving contacts, mounted or arranged to move in translation along said axis XX'.
A medium or high voltage circuit breaker according to any of claims 1 to 6, further comprising gas exhaust baffles (26) to remove hot gas generated by an opening of said pair of arcing contacts.
A medium or high voltage circuit breaker according to claim 7, said at least one cooling device (10) being on the path of said hot gas through or along said gas exhaust baffles.
A medium or high voltage circuit breaker according to any of claims 1 to 8, said casing being filled:
- with a gas comprising SF₆, or heptafluoroisobutyronitrile and/or heptafluoroisopropyl trifluoromethyl ketone (also named 2-butanone, 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)- (CAS No 756-12-7)) possibly mixed with a gas or a dilution gas comprising CO₂ and/or O₂ and/or N₂ and/or an oxygenated compounds, for example said comprising both CO₂ and a fluorinated compound, for example heptafluoroisobutyronitrile and/or heptafluoroisopropyl trifluoromethyl ketone;

- or with a gas comprising at least SF₆, and/or CO₂ and/O₂ and/or N₂ and/or an oxygenated compound.
A medium or high voltage circuit breaker according to any of claims 1 to 9, said circuit breaker being of the Gas-Insulated Switchgear (GIS) type, or of the Generator circuit breaker (GCB) type or of the Dead Tank type or of the Live Tank type.
A method for opening a circuit breaker according to any of claims 1 to 10, comprising:
- separating the movable contact (12) from the contact (5) of the circuit breaker, thereby generating hot gas;

- flowing at least part of said hot gas through said cooling device.
A method according to claim 11, said hot gas being at a temperature higher than 2000 K at the lattice inlet and a temperature reduced by 100 K or more at the outlet.
A method according to claim 11 or 12, said hot gas being at a temperature T₁ between 1500 K and 5000 K at the lattice inlet and a temperature T₂ < T₁ at the lattice outlet.
A method according to any of claims 11 to 13, said hot gas having a speed between 5 m/s and 400m/s at the lattice inlet.