EP2553705B2 - Fuse and circuit breaker comprising such a fuse - Google Patents

Description

The present invention relates to a fuse comprising an insulating bar and at least one fuse blade wound on this bar. The invention also relates to a combined switch comprising at least one such fuse. The field of the invention is that of high voltage fuses fitted to the combined switches.

In particular, the invention relates to a high voltage fuse for protecting cables and MV / LV distribution transformers (medium voltage / low voltage).

The fuse can provide this protection alone, or by being associated with a combined switch. In this case, it is equipped with a striker which causes the automatic opening of the switch following the operation of the fuse. The combination of the two devices, fuse and switch, is characterized by a transition current, for which they exchange the breaking function: above this value, the current is interrupted only by the fuses, below it is interrupted on a phase by the first fuse that melts, and by the switch on the other two phases.

Advantageously, the fuse must have a fast response, cutting off when the current increases beyond a predetermined value. In case of overcurrent or short-circuit, the fuse is cut by melting fusible elements, the faster the overcurrent is important.

An essential component of the fuse is therefore the fuse element, which conventionally is wound on an insulating bar disposed in the body of the fuse. The fuse element undergoes a rise in temperature proportional to the intensity of the current flowing through it. In normal operation, the temperature of the fuse element is below its melting temperature and the current flows normally. In case of overcurrent, the temperature of the fuse element exceeds the melting temperature at one or more points of the fuse element, which melts at least partially, and the flow of current is cut off.

US-2007/0159291 describes a fuse, with one or more fusible elements arranged on an insulating central bar. Each fuse element includes a main portion and a plurality of reduced sections arranged in series along its entire length. These reduced sections offer greater resistance than the main portions at the passage of the current, their temperature therefore increases until melting when the intensity of the current reaches a sufficient value. However, the response of the fuse is not always satisfactory at certain critical intensities, for which the cut-off time is too slow.

GB-A-2 184 301 discloses a fuse comprising a fuse element. On this element are delimited, on the one hand, a running part provided with several reduced sections of a first type and, secondly, an end portion provided with one or more reduced sections of a second type. The response of this fuse is not fast enough to be effective, especially for so-called "intermediate" intensities, corresponding to a melting time of between 10 milliseconds and 1 second.

The object of the present invention is to provide a fuse having a faster response, particularly for currents neighboring the transition current when associated with a switch.

For this purpose, the subject of the invention is a fuse as defined in claim 1.

Thus, a fuse element comprising reduced section areas of different types, having different minimum widths, and arranged alternately in its longitudinal direction, makes it possible to produce a fuse having an improved, fast response regardless of the intensity for which the fuse needs to be cut. The response of the fuse is notably improved for so-called intermediate fault intensities, for which the cut-off time is between 10 milliseconds and 1 second.

Other advantageous features of the invention, taken alone or in combination, are specified in the dependent claims.

The invention also relates to a combined switch comprising at least one fuse as mentioned above.

• la figure 1 est une vue en perspective d'un fusible conforme à l'invention ;
• la figure 2 est une coupe du fusible dans le plan II de la figure 1 ;
• la figure 3 est une coupe du fusible dans le plan III de la figure 2, avec une partie de son barreau central en vue extérieure ;
• la figure 4 est une vue en élévation d'un élément fusible équipant le fusible des figures 1 à 3 ;
• les figures 5 et 6 sont des vues à plus grande échelle des détails V et VI à la figure 4 ;
• les figures 7, 8, 9 et 10 sont des vues en élévation et de détails analogues aux figures 4 à 6 pour un second mode de réalisation d'un élément fusible équipant un fusible conforme à l'invention, et
• la figure 11 est un graphe illustrant la réponse du fusible des figures 1 à 6.

The invention will be better understood on reading the following description given solely by way of nonlimiting example and with reference to the drawings in which:

• the figure 1 is a perspective view of a fuse according to the invention;
• the figure 2 is a fuse cut in the plane II of the figure 1 ;
• the figure 3 is a fuse cut in the plane III of the figure 2 , with a part of its central bar in external view;
• the figure 4 is an elevational view of a fuse element fitted to the fuse of Figures 1 to 3 ;
• the Figures 5 and 6 are larger-scale views of details V and VI to the figure 4 ;
• the Figures 7, 8, 9 and 10 are views in elevation and details similar to Figures 4 to 6 for a second embodiment of a fuse element fitted to a fuse according to the invention, and
• the figure 11 is a graph illustrating the fuse response of Figures 1 to 6 .

On the Figures 1, 2 and 3 is represented a fuse 1 according to the invention. The figure 1 is an overview of the fuse 1. The figures 2 and 3 show the fuse 1, respectively in cross-section and in longitudinal section.

The fuse 1 comprises a substantially tubular fuse body 2 defining a longitudinal axis X-X '. The body 2 is made of insulating material, preferably porcelain.

At each of the longitudinal ends 1a or 1b of the fuse 1 is arranged a capsule 3a or 3b, adapted to conduct the electric current, and preferably made of metal. One of the capsules 3a or 3b may include a striker assembly 9 provided with a spring 91.

Inside the tubular body 2 is arranged a central bar 4, which extends between the two ends 1a and 1b of the fuse, parallel to the axis X-X '. The bar 4 is made of insulating material, preferably ceramic. As visible on the figure 2 , the bar 4 has a star-shaped cross section with six branches. When the bar 4 is positioned inside the body 2, its central and longitudinal axis X4 coincides with the axis X-X '. The intermediate volume 8 between the bar 4 and the body 2 of the fuse 1 is filled with sand, not shown.

In a variant not shown, the fuse 1 may comprise two concentric bars arranged in the body 2.

Between each capsule 3a and 3b and the bar 4 is positioned an electrically conductive contact piece, respectively 6a and 6b, preferably made of metallic material. The contact parts 6a and 6b each comprise six lugs 61a and 61b, which extend radially towards the body 2 and make it possible to connect the fuse elements. The contact pieces 6a and 6b also comprise positioning elements 62a and 62b, which allow correct alignment with the bar 4, and electrical contact tabs 63a and 63b. Each contact piece 6a and 6b is connected to the bar 4 by a fastener 71a and 71b, respectively.

The bar 4 comprises a central through hole 41 of substantially circular shape, in which is housed a spiral fuse wire 22, also called striker wire. On the side facing the end 1a of the fuse 1, the striker wire 22 is connected to the striker assembly 9 by a metal tube 23 which comprises in particular crimping zones for holding the striker wire 22. On the side facing the end 1b of the fuse 1, the striker wire 22 is connected to one of the contact tabs 63b.

When an overcurrent causes the fuse 1 to melt, the moving part of the striker assembly 9 is released and actuates the mechanism of the switch and / or makes it possible to signal the state of the fuse.

A conductive fuse element 110 is spirally wound around the bar 4, between the two contact pieces 6a and 6b. In practice, the fuse element 110 is a fuse link, silver (Ag). On the figure 3 , a central portion of the bar 4 is shown in an external view, to show the winding of the blade 110 on the bar 4. The ends of the blade 110 are connected to the lugs 61a and 61b of the contact parts 6a and 6b, which are themselves connected to the respective capsules 3a and 3b. The connections between conductive parts are made by welding, or any other known means.

The fuse blade has a thickness e110 constant, this thickness being measured perpendicularly to the plane of Figures 4 to 6 , that is to say in a radial direction relative to the axis XX 'in the wound configuration of the blade 110 on the bar 4. X110 is a longitudinal axis of the blade 110, this axis being straight in the configuration of the Figures 4 to 6 and spiral in the configuration of the figure 3 . The blade 110 has a maximum width ℓ110, measured perpendicular to its thickness e110 and the axis X110, at several segments 111 distributed along the length of the blade 110. The segments 111 are separated by reduced sections 112 and 113 of two different types. The reduced sections 112 and 113 are evenly spaced along the blade 110 along its longitudinal axis X110. More precisely, as shown in figure 4 the reduced sections 112 and 113 are alternately distributed along the blade 110 and are disjoint, i.e. do not overlap.

As visible on the figure 5 , each section 112 of the first type has two recesses 112a and 112b whose edge is in an arc, opposite symmetrically with respect to the axis X110.

As visible on the figure 6 each section 113 of the second type has two recesses 113a and 113b, each of substantially rectangular shape, symmetrically opposite to the axis X110.

In the following, a length of a portion of the fuse blade is measured parallel to its longitudinal axis.

est compris entre 1,1 et 1,4.The recesses 113a and 113b have a length L113 greater than the length L112 of the recesses 112a and 112b. The minimum width ℓ113 of the band 110 at a reduced section 113 of the second type is greater than the minimum width ℓ112 at a reduced section 112 of the first type. More precisely, the ratio of these widths $\frac{\mathcal{l}113}{\mathcal{<figure-callout\; id="112"\; label="l"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">l</figure-callout>}112}$

is between 1.1 and 1.4.

In practice, the reduced sections 112 of the first type are more numerous than the reduced sections 113 of the second type. For example, as visible on the figure 4 , the blade 110 comprises a succession of eight sections 112, then a section 113, and so on alternately along the blade 110. Between the reduced sections 112 and 113, there are segments 111 of maximum width ℓ110.

In variant not shown, the blade 110 may comprise a succession of six, seven or nine sections 112 between two sections 113, and so on alternately along the blade 110. The blade 110 does not comprise a first elongate portion provided with sections 112 and a second elongated portion provided with sections 113, without alternation between the reduced sections of different types, as is the case in GB-A-2 184 301 .

On the Figures 7, 8, 9 and 10 is shown a second embodiment of a fuse blade 210 which can equip a fuse according to the invention.

Fusible blade 210 has a constant thickness, this thickness being measured perpendicularly to the plane of Figures 7 to 10 , that is to say in a direction radial with respect to the axis XX 'in wound configuration of the blade 210 on the bar 4. X210 is a longitudinal axis of the blade 210, this axis being rectilinear in the configuration of the Figures 7 to 10 and spiral in a configuration similar to that of the figure 3 . The blade 210 has a maximum width ℓ210, measured perpendicular to its thickness and to the axis X210, at several segments 211 distributed along the length of the blade 210. The segments 211 are separated by reduced sections 212, 213 and 214 of three different types, which are evenly spaced along the blade 210 along its longitudinal axis X210. More precisely, as shown in figure 7 the reduced sections 212, 213 and 214 are alternately distributed along the blade 210 and are disjointed, i.e., do not overlap.

As visible on the figure 8 , each section 212 of the first type has two recesses 212a and 212b whose edge is in an arc, opposite symmetrically with respect to the axis X210.

As visible on the figure 9 each section 213 of the second type has two recesses 213a and 213b, each of substantially rectangular shape, symmetrically opposite to the axis X210.

As visible on the figure 10 each section 214 of the third type has two recesses 214a and 214b, each of substantially rectangular shape, symmetrically opposite with respect to the axis X210.

The recesses 213a and 213b have a length L213 greater than the length L212 of the recesses 212a and 212b. The minimum width ℓ213 of the web 210 at a reduced section 213 of the second type is greater than the minimum width ℓ212 at a reduced section 212 of the first type.

et $\frac{\mathcal{l}214}{\mathcal{l}212}$

sont compris entre 1,1 et 1,4. De plus, le rapport $\frac{\mathcal{l}214}{\mathcal{l}213}$

est compris entre 1 et 1,4.The recesses 214a and 214b have a length L214 greater than the length L213 of the recesses 213a and 213b of a reduced section 213 of the second type. The minimum width ℓ214 of the web 210 at a reduced section 214 of the third type is greater than or equal to the minimum width ℓ213 at a reduced section 213 of the second type. In particular, the ratios of the minimum widths $\frac{\mathcal{l}213}{\mathcal{<figure-callout\; id="212"\; label="l"\; filenames="imgf0004.png"\; state="\{\{state\}\}">l</figure-callout>}212}$

and $\frac{\mathcal{l}214}{\mathcal{<figure-callout\; id="212"\; label="l"\; filenames="imgf0004.png"\; state="\{\{state\}\}">l</figure-callout>}212}$

are between 1.1 and 1.4. In addition, the report $\frac{\mathcal{l}214}{\mathcal{<figure-callout\; id="213"\; label="l"\; filenames="imgf0004.png"\; state="\{\{state\}\}">l</figure-callout>}213}$

is between 1 and 1.4.

In practice, the reduced sections 212 of the first type are more numerous than the reduced sections 213 of the second type, and the reduced sections 213 of the second type are themselves more numerous than the reduced sections 214 of the third type. For example, as visible on the figure 7 the blade 210 comprises a succession of seven sections 212, then a section 213, and so on. In addition, a section 213 of seven is replaced by a section 214. Between the reduced sections 212, 213 and 214, there are the segments 211 of maximum width ℓ110.

In a variant not shown, the blade 210 may comprise a succession of six, eight or nine sections 212 between two sections 213 or 214, and so on alternately along the blade 210.

In normal operation of the fuse 1, the temperature of the fuse elements increases by Joule effect, up to a value at which it stabilizes. In particular, this Joule effect creates a temperature increase which varies at different points of the fuse link 110 or 210.

Thus, the particular configuration of a fuse blade 110 or 210 according to the invention makes it possible to favor certain melting zones, since the reduced sections 112, 113, 212, 213 and 214 dissipate heat less than the segments 111 and 211. Indeed, the geometry of the reduced sections influences their heat exchange with the nearby environment. The different sections of the same type, having identical heat exchanges, melt substantially at the same time at different points of the fuse blade, this time required for the melting depending on the overcurrent flowing in the fuse blade and causes its heating. For example, for an identical section width and length, an arcuate recess dissipates heat better than a recess of rectangular shape because the section includes more material. However, for a very high intensity, the minimum width of the reduced section is a predominant parameter in front of the shape of the recess, because the section melts at its center first, and not homogeneously.

Thus, when overcurrent occurs, some sections may melt faster than others. When the blade has only one type of section reduced, its response curve "cutoff time / cutoff intensity" has a given aspect. By combining different types of reduced sections, we obtain a response curve which is the superposition of each of the response curves corresponding to each of the sections.

At the highest intensities, corresponding to a very short fuse cut-off time, sections with the smallest minimum width melt first. In the embodiments described, this corresponds to the reduced sections of the first type 112 and 212. When the overcurrent is less, with a slightly longer cut-off time, the length and the particular geometry of the sections are taken into account. Thus, with their rectangular recesses and their longer length, the reduced sections 113, 213 and 214 of the second and third types are likely to melt before those of the first type 112 and 212. The operation of the fuse 1 is thus made faster in a range of particular intensities.

In practice, a blade according to the first embodiment is simpler to manufacture because it requires a number of machining and / or reduced forming operations for only two different types of reduced sections, while a blade according to the second embodiment comprises three different types of reduced sections but allows to obtain a different response curve.

Alternatively, the blade may comprise more than three different types of reduced sections, although this makes it more complex to manufacture.

According to another variant, the geometries, minimum widths, lengths and shape of the recesses of the different types of reduced sections may vary. For example, in the second embodiment, the reduced sections of the third type have a greater width and a greater length than the reduced sections of the second type. Alternatively, the reduced sections of the third type may have the same minimum width.

In addition, a recess can be triangular, elliptical, crenellated, or any other geometry.

On the figure 11 is represented a graph illustrating the operation of the fuse 1 equipped with the fuse blade 110. This fuse 1 is in accordance with the first embodiment described above in connection with the Figures 1 to 6 .

The graph of the figure 11 shows the cut-off time "t" in seconds (s), represented on the ordinates, as a function of the intensity "I" of the fault current in amperes (A), represented on the abscissa, according to a logarithmic scale.

Curve C1 in solid line corresponds to the behavior of a fuse equipped with a blade having only reduced sections of the first type, similar to 112, regularly spaced along this blade.

Curve C2 in dashed lines corresponds to the behavior of fuse 1 equipped with a blade 110, comprising alternately eight reduced sections of the first type 112 and a reduced section of the second type 113, and so on alternately along the blade 110 .

In practice, the fuse 1 breaking time according to the invention is reduced for so-called "intermediate" intensities, corresponding to a melting time of between 10 milliseconds and 1 second, without changing or very little fuse 1 response for the low intensities, corresponding to a melting time greater than or close to 10 seconds. The cut-off time corresponds to the fusion of the reduced sections of a specific type as a function of the intensity of the fault current.

Claims (13)

1. High voltage fuse (1) comprising:

   - a tubular body (2),

   - at least one insulating bar (4) arranged in the tubular body along a longitudinal axis (X-X') of the tubular body, and

   - at least one fuse strip (110; 210) of a constant thickness (e110), arranged on the bar (4) and extending between the longitudinal ends (1a, 1b) of the fuse (1), the strip (110; 210) comprising segments (111; 211) of a maximum width (l110; l210) and several narrow sections (112, 113; 212, 213, 214) arranged along its longitudinal direction, with each narrow section having a geometry defined by its minimum width (l112, l113; l212, l213, l214) and its length (L112, L113; L212, L213, L214),

   wherein the narrow sections (112,113; 212, 213, 214) are of at least two different types and include:

   - at least one narrow section of a first type (112; 212) which has a first minimum width (l112; l212), and

   - at least one narrow section of a second type (113; 213) which has a second minimum width (l113; l213), different from the first minimum width,

   characterised in that the narrow sections (112, 113; 212, 213, 214) are regularly spaced along the fuse strip (110; 210), with an alternation of narrow sections of the first type (112; 212) and narrow sections of the second type (113; 213), in that the strip (110; 210) comprises an alternation of several narrow sections of the first type (112; 212) between two narrow sections of the second type (113; 213) and in that the minimum width (l112; l212) of a narrow section of the first type (112; 212) is less than the minimum width (l113; l213) of a narrow section of the second type (113; 213), with the ratio of the second minimum width over the first minimum width $\left(\frac{\mathcal{l}113}{\mathcal{l}112},\mathrm{}\frac{\mathcal{l}213}{\mathcal{l}212}\right)$

   

   between 1.1 and 1.4.
2. Fuse according to claim 1, characterised in that the strip (110; 210) comprises a succession of six to nine narrow sections of the first type (112; 212) then a narrow section of the second type (113; 213), and so on in alternation along the strip (110; 210).
3. Fuse according to one of the preceding claims, characterised in that the strip (110; 210) comprises a succession of seven or eight narrow sections of the first type (112; 212) then a narrow section of the second type (113; 213), and so on in alternation along the strip (110; 210).
4. Fuse according to one of the preceding claims, characterised in that each narrow section of the first type (112; 212) includes at least one recess (112a, 112b; 212a, 212b) of which the edge is an arc or circle.
5. Fuse according to one of the preceding claims, characterised in that each narrow section of the second type (113; 213) includes at least one recess (113a, 113b; 213a, 213b) of a substantially rectangular shape.
6. Fuse according to one of the preceding claims, characterised in that the length (L112; L212) of a narrow section of the first type (112; 212) is less than the length (L113; L213) of a narrow section of the second type (113; 213).
7. Fuse according to one of the preceding claims, characterised in that the strip (210) comprises at least one narrow section of a third type (214), having a third minimum width (l214) different from those (l212, l213) of the narrow sections of the first and second types (212, 213), with the ratio of the third minimum width over the first minimum width $\left(\frac{\mathcal{l}214}{\mathcal{l}212}\right)$

   

   between 1.1 and 1.4.
8. Fuse according to claim 7, characterised in that the narrow section of the third type (214) includes at least one recess (214a, 214b) of substantially rectangular shape.
9. Fuse according to one of claims 8 or 9, characterised in that the minimum width (l213) of a narrow section of the second type (213) is less than or equal to the minimum width (l214) of a narrow section of the third type (214), and the length (L213) of a narrow section of the second type (213) is less than or equal to the length (L214) of a narrow section of the third type (214), with the lengths (L213, L214) not equal in the case where the widths (l213, l214) are equal, with the ratio of the third minimum width over the first minimum width $\left(\frac{\mathcal{l}214}{\mathcal{l}213}\right)$

   

   between 1 and 1.4.
10. Fuse according to one of claims 7 to 9, characterised in that the strip (110; 210) comprises a greater number of narrow sections of the first type (112; 212) than narrow sections of the second type (113; 213) and, where applicable, a greater number of narrow sections of the second type (213) than narrow sections of the third type (214).
11. Fuse according to one of claims 7 to 10, characterised in that the strip (110; 210) comprises a succession of seven or eight narrow sections of the first type (112; 212) then a narrow section of the second type (113; 213), and so on in alternation along the strip (110; 210), and in that one narrow section of the second type (113; 213) out of seven is replaced by a narrow section of the third type (214).
12. Fuse according to one of the preceding claims, characterised in that the narrow sections of the first type and the narrow sections of the second type, and where applicable, the narrow sections of a third type, are separated.
13. Combined switch, characterised in that it comprises at least one fuse (1) according to one of the preceding claims.

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