Patent Grant
8835790
The invention relates to medium-voltage vacuum circuit-breakers, sometimes called vacuum bottles.
It relates more particularly to improving arc extinction in such vacuum circuit-breakers.
The main application is that in which vacuum circuit-breakers are used as break switches in alternating current (AC) generator disconnector circuit-breakers at the outlet from a power station.
Vacuum circuit-breakers have been used for very many years in medium-voltage electrical distribution switchgear to break short-circuit currents of the order of a few kiloamps (kA), typically 25 kA, at a few kilovolts (kV), typically 36 kV. In this type of distribution switchgear, vacuum circuit-breakers need also to withstand continuous current, typically of the order of 1250 amps (A) without overheating. The way they are implanted in the distribution network is such that those vacuum circuit-breakers are closed in normal operation of the network and they carry the continuous nominal current.
It is known in the art that in order to break such short-circuit currents, it is necessary to design the arcing contacts so that an intense axial magnetic field (AMF) or an intense radial magnetic field (RMF) is generated at their facing ends in order to extinguish the arc upon separation of the contacts.
In other words, breaking high currents in vacuum circuit-breakers requires the arcing contacts to have such arc control means incorporated therein: the arcing contacts therefore form an integral part of the vacuum circuit-breaker.
The function that these arc control means are expected to perform is to ensure the energy density of the arc created through the arcing contacts while the current is being broken remains below the limits required both for breaking the current and also for withstanding the recovery voltage in the vacuum space immediately after the current has been interrupted.
The above-mentioned AMF is generated parallel to the axis of the vacuum circuit-breaker whereas the likewise above-mentioned RMF creates a magnetic force that causes the arc to rotate at the periphery of the mechanical surface of the contact.
Such an AMF or RMF is created by the current itself as it flows through the arc control contacts.
Typically, the arc control means generating the AMF or RMF comprise two windings, one of which is mounted in the movable arcing contact and the other in the stationary arcing contact of a vacuum circuit-breaker. If the current flows in the same direction in both windings, the resulting magnetic fluxes add together in an axial direction of the vacuum circuit-breaker in the vacuum space between the two arcing contacts while opening or when separated from each other. If the current flows in a given winding in the opposite direction to the flow in the other winding, that results in a magnetic flux that extends radially in the vacuum space between the two separate arcing contacts.
The arc control means generating AMF theoretically have the first technical effect of preventing the arc from contracting in a precise zone. In other words, they need to enlarge the arc over a contact area that is as large as possible. The looked-for result is thus to spread the energy of the arc over an area that is as large as possible and that will thus enable the AC to be broken at the natural zero-crossing.
Effective AMF arc control means must therefore generate a high and uniform magnetic flux over the entire surface of the contact.
Typically, the breaking of currents in the range 30 kA to 50 kA requires the use of contacts of diameter lying in the range 50 millimeters (mm) to 80 mm. For such diameters, the AMF arc control means that are presently implemented give overall satisfaction.
However, certain vacuum circuit-breakers are used in applications where they may be subjected to short circuit currents for breaking of a few kiloamps, typically 63 kA, 80 kA to 160 kA. That necessarily requires the use of contacts of greater diameter, typically lying in the range 90 mm to 150 mm.
With such diameters, the inventors have found that an AMF is created with non-uniform distribution over the physical contact surface with a weaker field in the central portion, which causes the breaking performance of the vacuum circuit-breaker to be reduced.
Solutions have already been proposed for improving the magnetic flux generated by the contacts of a vacuum circuit-breaker, while also enabling them to withstand continuous currents in the closed position.
Some existing solutions entail either implanting additional ferromagnetic materials in the winding portion of the contact and/or in the electrode portion, or else producing slots in the contact body in order to reduce eddy currents locally, or else to combine both solutions.
Where implanting ferromagnetic materials is concerned, the U.S. Pat. No. 6,747,233 B1 discloses the use of magnetic rings with different saturations and permittivities μ in order to have magnetic fields of different profiles and different values as a function of the magnitudes of the currents, i.e. different for low currents and for high currents. To be more precise, both a saturable magnetic material 101, 401 and a non-saturable magnetic material 102, 402 are implanted in a contact body 104, 404 that is solid and essentially conductive and that is itself fastened to a mechanical connection rod portion 103 that is essentially conductive. In the embodiment envisaged, the relative values of the electrical resistivity of the saturable materials are the opposite of those of the non-saturable materials. Accordingly, in the embodiment shown in FIGS. 1A to 3, the saturable material 101 has high electrical resistivity and is implanted around a non-saturable material 102 that has low electrical resistivity. The major drawback of using ferromagnetic materials in contacts is that the contacts are magnetized and therefore subjected as it were to the force produced by the magnetic field. This force is reversed every 10 milliseconds (ms) for sinusoidal AC at a frequency of 50 hertz (Hz). The continuous presence of this force on the materials that are supposed to control the short-circuit arc tends to weaken the structure of the contact itself. Furthermore, the value of the magnetic field obtained with inserted ferromagnetic materials is not necessarily higher than that obtained without them.
The patents DE 195 03 661 and U.S. Pat. No. 4,390,762 each disclose a combined solution of producing slots and of implanting additional ferromagnetic materials.
To be more precise, patent DE 195 03 661 discloses a contact 1 comprising a hollow cylindrical tube 2 as the mechanical connecting rod portion, to which there is fastened the contact portion proper 3, which is magnetic. That magnetic contact portion 3 is hollow in its center and has a solid cylindrical winding portion 4 and an electrode disk portion 8 separated by a magnetic spacer 9 and a stainless steel or ceramic plate 10. Three identical spiral slots 5 are formed in the hollow contact 3 at 120° to one another, extending from its inside diameter 7, which coincides with the outside diameter of the tube 2, to its outside diameter 6. That kind of geometry produces a magnetic field that extends axially while also being radially distributed, and therefore creates a rotating arc that reaches a larger area of the contacts. In other words, that document discloses generating a radial magnetic field that causes the arc to turn in an annular zone at the periphery of the contacts.
U.S. Pat. No. 4,390,762, discloses a contact with a tubular mechanical connecting rod portion 1 to which there is fastened a cylindrical base 2 with a hollow center and that constitutes the winding portion of the contact, to which there is fastened a low annular contact ring 4. The mechanical connecting rod 1 and the cylindrical base are essentially made of copper, whereas the annular contact ring 4 is based on a chromium matrix saturated with copper. As can be seen in FIG. 2, the winding portion 2 comprises two concentric portions 3 separated by a high-grade steel 6 that fills a vertical annular hollow 5. Rectilinear radial slots are produced over a portion of the height of each of these portions 3. The slots are uniformly distributed over the periphery and oriented at the same angle of inclination to the axis of the cylinder 2, without intersecting it. The structure disclosed in that document increases the mechanical strength of the contacts.
Another existing solution is that described in the TOSHIBA publication, Proceedings ISDEIV 1998, pages 417-418, entitled “Physical and theoretical aspects of a new vacuum arc control technology”. That solution consists in adding a second winding that is smaller than the first winding. The drawback of that solution is that the magnetic fields generated by the windings described are mutually opposed, which tends to reduce considerably the effective total magnetic field.
In order to resolve that problem, in the patent application FR 09 53852, filed on Jun. 10, 2009, and entitled “Contact pour ampoule à vide à moyenne tension à coupure d'arc améliorée, ampoule à vide et disjoncteur, tel qu'un disjoncteur sectionneur d'alternateur associés” [A contact for a medium-voltage vacuum circuit-breaker with improved arc extinction, and an associated vacuum circuit-breaker and circuit-breaker, such as an AC generator disconnector circuit-breaker] the Applicant has proposed a second winding electrically in parallel with the first winding and adapted to generate a magnetic field that is superposed on the magnetic field generated by the first winding.
That solution is generally satisfactory in the sense that it does indeed make it possible to increase the AMF and avoid it weakening at its center, by giving it a given profile that is effective over the entire surface of the end contact.
Patent DE 195 13790 describes a winding 33 for generating an AMF in a vacuum circuit breaker contact, and in its embodiment of FIG. 5, it has helical slots 50 of limited length that do not enable a magnetic field to be obtained that is uniform both at the surfaces of the arc control contacts and in the space between the contacts of the circuit breaker.
An object of the invention is to propose an improved solution that makes it possible to further increase the AMF in an electrical contact for a medium-voltage vacuum circuit-breaker, while avoiding weakening of the field at the center of the contact.
Another object of the invention is to improve the uniformity of the magnetic field over the surfaces of the contacts and in the space between the contacts of a vacuum circuit breaker, while reducing the cost of manufacture.
To do this, the invention provides a winding based on a material of low electrical resistance, such as copper, and of diameter typically greater than 90 mm, intended to create a magnetic field in an electrical contact for a medium voltage vacuum circuit-breaker, the winding consisting of a hollow cylinder including helical slots about its longitudinal axis that are parallel to one another and that open out both to the hollow and to the outside of the cylinder.
According to the invention, the angular length of each helix is equal to at least 360°. It is stated here that the notion of “angular length” of the helixes is to be understood in the usual mathematical sense: thus, in considering the projection of a helix on a plane perpendicular to its axis, the angular length of a helix is the value of the angle traveled by moving along its length between its two ends.
By methodically making helical slots that are parallel to one another with an angular length equal to at least 360°, the drawbacks of prior art windings are overcome.
The inventors have found that prior art windings with helical slots of shorter length generate non uniformity in the magnetic flux when the arc is created in a concentrated zone, in particular in a zone at the periphery of the contact having the winding. In prior art windings, at least for a certain time period, the current flows only in a limited portion of the strands that are defined individually by two slots. This is due to the fact that the arc may start from any point on the surface (the last point of contact for the two electrodes before they separate). It is very rare, or even impossible, to have more than one point of separation between the two surfaces of the two contacts. The other portions of the strands contribute little or not at all to generating the total magnetic flux. This is what concentrates the AMF even though it ought to be distributed over the entire surface of the arc so as to diffuse the arc. In addition, and even if the arc manages to be fed very quickly by all of the arc control strands, there remain zones of weak field, or in other words “wells”, created by the discontinuities of the strands between one another. These weak magnetic field zones increase the risk of constriction. These zones of non-uniformity in the magnetic field of a winding imply there will be zones of non-uniformity in the magnetic field in the space between the two contacts, thereby giving rise to zones in which the plasma is disturbed while interrupting current. The harmful consequence is obtaining thermal loading that is not uniform over the surfaces of the contacts. For high short-circuit current values, this can affect the circuit-breaking performance of a vacuum circuit breaker. The larger the diameter of the arc control, the larger these weak field zones. The smaller the number of strands, the larger the zones (with geometry similar to that of the prior art in
The AMF field generated by the winding of the invention implanted in a medium voltage contact is uniform, i.e. symmetrical and constant, both at the surface of the contact and in the space between the contacts, and of a value that is much higher than the flux generated by prior art windings.
For an angular length value of at least 360°, a winding of the invention may generate an AMF that is increased by a factor of 2 to 3 relative to the flux generated by a prior art winding.
Further, a winding of the invention makes it possible to increase the mechanical endurance of a contact that is of large size, typically lying in the range 90 mm and 150 mm, and in which the winding is incorporated.
In addition, the stability of the AMF arc control when the current is broken is improved with a winding of the invention. The inventors have found that for winding lengths of less than 360°, the AMF is not necessarily uniform when the arc is created locally. In this event, the current flows in preferred manner in one or two strands of the winding, at least for a certain time period. Thus, the other strands contribute little or not at all to obtaining the total magnetic field. This results in the AMF being localized whereas in order to be effective it should be distributed over the largest possible area of the contact. Thus, a winding of the invention with helical slots of angular lengths that are equal to at least 360° generate an AMF that is high and uniform whatever the position of the initial arc.
Preferably, the width of each slot is less than 0.5 mm for an outside diameter φ ext of the hollow cylinder that is greater than 90 mm.
Preferably still, each strand individually defined by two consecutive helical slots presents a section parallel to the longitudinal axis of the winding that is substantially rectangular and identical over the entire height of the winding.
In an advantageous characteristic, the number of parallel helical slots is equal to at least two, and advantageously equal to six.
The invention also provides a method of making a winding based on a material of low electrical resistance, such as copper, intended to generate a magnetic field in an electrical contact for a medium voltage vacuum circuit-breaker, the method including the step of making a hollow cylinder with helical slots arranged around its longitudinal axis, and opening out both to the hollow and to the outside of the cylinder, the cylinder being empty of material, in which step the angular length of each helical slot is equal to at least 360°.
Advantageously, the helical slots of angular length greater than or equal to 360° are made by electric discharge machining. The method of making a winding of the invention is of reduced cost because the number of operations required for making the slots is also reduced.
Compared to the shape of
The invention also provides an electrical contact for a medium voltage vacuum circuit-breaker extending along a longitudinal axis Y and comprising:
In a variant, the helical slots of the first winding are of the right-handed type going from the mechanical connection portion to the circular contact plate. It is stated here that the term “right-handed” is as used in mathematics and means that an observer placed outside the contact sees the helixes going from left to right going from the mechanical connection portion towards the circular plate.
In an advantageous embodiment, the contact includes a second winding, of an arrangement that is the subject matter of the patent application FR 09 53852, filed on Jun. 10, 2009 by the Applicant and entitled [A contact for a medium-voltage vacuum circuit-breaker with improved arc extinction, and an associated vacuum circuit-breaker and circuit-breaker, such as an AC generator disconnector circuit-breaker].
This second winding is thus connected electrically in parallel with the first winding and is adapted to generate a magnetic field that is superposed on the magnetic field generated by the first winding.
In a first variant, the second winding may be constituted by a winding of the invention, with an angular length of each slot equal to at least 360°.
The second hollow cylinder is thus centered on the longitudinal axis Y, concentric with the first cylinder, having one end fastened to the mechanical connection portion and the other end fastened to the circular plate, the hollows of the cylinders being empty of material.
The helical slots of the second winding are of the right-handed type going from the mechanical connection portion to the circular contact plate.
The method of manufacture used (wire electric discharge machining) enables the second winding to be made at the same time as the main winding and by cutting the same block of material. There is therefore no additional part or additional cutting pass.
In an advantageous embodiment, the contact includes at least one column, such as is claimed in the patent application FR 09 53853, filed on Jun. 10, 2009 by the Applicant and entitled “Contact pour ampoule à vide à moyenne tension à structure renforcée, ampoule à vide et disjoncteur, tel qu'un disjoncteur sectionneur d'alternateur associés” [A contact for a medium-voltage vacuum circuit-breaker with reinforced structure, and an associated circuit breaker or vacuum circuit-breaker, such as an AC generator disconnector circuit-breaker]. The column is thus distinct from the winding(s) and arranged, in the hollow of the first cylinder, as a spacer between the mechanical connection portion and the circular plate of the contact body in such a manner as to avoid the collapse thereof during a closing operation and in the closed position of the vacuum circuit-breaker, the column(s) having high electrical resistance such that when a given current flows in the contact, the amount of current that flows in the column(s) is negligible relative to the current that flows in the winding(s).
The outside diameter of the first winding and of the circular plate lies in the range 90 mm and 150 mm, and that is completely suitable for an application in which the short-circuit currents to be broken have a value greater than or equal to 63 kA, typically up to 100 kA.
The invention also provides a medium voltage vacuum circuit-breaker comprising at least one electrical contact described above.
The vacuum circuit-breaker may include a pair of electrical contacts with one stationary contact as described above and a movable contact as described above.
Preferably, in the vacuum circuit-breaker, the slots of the windings of angular length that is greater than 360° open out to the side of the separating space between contacts where the arc is formed when the current is broken.
The invention also provides a circuit breaker, such as an AC generator disconnector circuit-breaker comprising at least one vacuum circuit-breaker as described above.
As a function of the application, a vacuum circuit-breaker of the invention may or may not carry the nominal load current, and it naturally carries the short-circuit current in the event of a fault
Other advantages and features of the invention emerge more clearly on reading the detailed description given by way of non-limiting illustration with reference to the following figures, in which:
As shown in
The contacts 2, 3 in a vacuum circuit-breaker are usually separated in order to extinguish an arc that is liable to be produced in the separation space 5 between these contacts.
Whether in the closed position or the open position, the contacts 2, 3 are inside a shield 6 that is itself inside the jacket 7 of the circuit-breaker, within which there is a vacuum.
Breaking high alternating currents requires the arc that is generated to be controlled.
The arc control means are usually an integral part of the vacuum circuit-breaker. They must therefore ensure that the energy density of the arc at the contacts 2, 3 remains below acceptable limits in order to be able to break the current and to withstand the transient recovery voltage TRV.
One known type of arc control is axial magnetic field (AMF) arc control.
This entails generating an AMF parallel to the longitudinal axis Y of the bottle 1.
These AMF arc control means are supposed to prevent contraction of the arc and consequently to enlarge it over an area of the facing surfaces of the contacts that is as large as possible. The normal result of this is to distribute the energy of the arc over a larger area and thus to enable the current to be broken at the natural zero-crossing of the alternating current.
In other words, in order to diffuse the arc effectively over the facing contact surfaces, efficient AMF arc control requires the production of a high and uniformly distributed magnetic field that is really generated by the winding.
Thus these AMF arc control means are constituted by a component in the form of a coil or winding that consists of a hollow cylinder 8 arranged as shown in
The hollow 80 of the winding 8 is empty of material. The hollow cylindrical winding 8 includes helical slots 81 around the longitudinal axis Y and opening out both to the inside and to the outside of the cylinder 8. The space between two consecutive slots 81 is defined by a strand 82.
Each contact 2, 3 includes a mechanical connection portion 20, 30 and a contact body 21, 31 fastened to this mechanical connection.
The body 21, 31 includes the winding 8 and an electrode portion 22, 32 in the form of a circular plate. This plate 22 or 32 constitutes the surface of mutual physical contact with the other plate 32 or 22 when the contacts are in the closed position.
These contact surfaces 22, 32 are therefore those over which the arc must be diffused as uniformly and as widely as possible.
Each winding 8 is fastened both to the mechanical connection portion 20 or 30 and to the circular plate 22 or 32.
The windings 8 and electrode portions 22, 32 of the invention typically have an outside diameter lying in the range 90 mm to 150 mm in applications in which the current to be broken has a value greater than or equal to 63 kA, e.g. 80 kA or higher.
Such an application that is particularly suitable is one in which the vacuum circuit-breaker is used as an AC generator circuit-breaker at the outlet of a power station.
Along this section, it can be seen that the slot portions 81 are uniformly distributed on the diameter of the winding 8 (twelve of them) and all have the same dimensions. The angular length of a slot 81 is α of the order of 115°. This configuration corresponds to that described in the patent application in the name of the Applicant No. FR 09 53855, filed on Jun. 10, 2009, and entitled: “Enroulement pour contact d'ampoule à vide à moyenne tension à endurance améliorée, ampoule à vide et disjoncteur, tel qu'un disjoncteur sectionneur d'alternateur associés” [A winding for a contact of a medium-voltage vacuum circuit-breaker with improved endurance, and an associated circuit breaker or vacuum circuit-breaker, such as an AC generator disconnector circuit-breaker].
As indicated up the ordinate (y axis) the maximum value of the AMF obtained is about 6.5 units.
The total effective magnetic field obtained with a prior art winding (
The inventors have sought to further increase the value of the magnetic field.
In other words the object of the invention is to generate a magnetic field of a high value while improving its uniformity on the contact surface and while reducing manufacturing costs.
In order to increase the total effective magnetic field in the contact, for contacts 2, 3 of large diameter (in the range 90 mm to 150 mm), the inventors have thus thought to increase the angular length of the helix of each slot 81.
The shape of the fields obtained respectively in
However, as indicated in ordinates in
Thus, the (circuit) gain in value of the AMF by means of the invention is equal to 3 (relationship between the maximum value of 19.5 of
Another electrical contact has been made according to the invention: it includes a first winding made as seen in
The second winding 9 is arranged concentrically in the first winding 8.
The second winding 9 is thus electrically connected in parallel with the first winding 8 and adapted to generate a magnetic field that is superposed on the magnetic field generated by the first cylinder 8.
It consists in a second hollow cylinder 9 including helical slots (not shown) about its axis and opening out both to the inside and outside of the cylinder. The second hollow cylinder 9 is centered on the longitudinal axis Y, concentric with the first cylinder 8, having one end fastened to the mechanical connection portion 20 and the other end fastened to the circular plate 22.
The two windings 8 and 9 are electrically mounted in parallel: thus the two cylinders are fastened to the base of connection 20 and to the electrode plate 22.
In contrast to the winding 8 of the invention, each helical slot of the second winding 9 is made with an angular length of at least 360°.
Preferably, the slots of angular length of at least 360° open out onto the plate 22 or 32, i.e. in the separating space 5 between contacts 2, 3 where the arc is formed when the current is broken.
The shape of the fields obtained respectively in
However, as indicated up the ordinate in
Thus, the (circuit) gain in value of the AMF by means of the invention is here of the order of 2.9 (relationship between the maximum value of 19 of
The above-described invention makes it possible to obtain the following advantages:
Other improvements are possible within the scope of the invention, namely making a winding 8 with helical slots 81 that are parallel to one another and of angular length equal to at least 360°. As described above, at least in part, it is possible to make an electrical contact 2, 3 that incorporates the winding of the invention and further:
| Number | Date | Country | Kind |
|---|---|---|---|
| 09 56744 | Sep 2009 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/064233 | 9/27/2010 | WO | 00 | 3/21/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/039133 | 4/7/2011 | WO | A |
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| 20120181254 A1 | Jul 2012 | US |
