EP0296915B1 - Rotating switch with curved arc-runner path - Google Patents

Abstract

A rotary switch with a sealed enclosure in which a rotating knife-blade is housed cooperating with two stationary contacts supported by the internal periphery of the enclosure. A permanent magnet is incorporated in the stationary contacts to magnetically blow the arc roots on a curved migration track towards hidden locations which are not facing the knife-blade. The invention is applicable to a gas-insulated medium voltage switch.

Description

The invention relates to a medium-voltage rotary switch with a sealed casing, the internal periphery of which carries two diametrically opposite fixed contacts, each fixed contact being capable of cooperating with a movable contact of a contact bridge to form a pair of contacts, said contact bridge, in the form of a pivoting knife, being carried by a rotary control shaft, which can selectively occupy a closed position in which the two pairs of contacts are closed and an open position.

A known rotary switch (EP-A-0.023.298) of the kind mentioned has internal gas compression compartments allowing pneumatic blowing of the arc which promotes its extinction. These pneumatic blowing devices are complicated and require a significantly increased effort in operating the switch.

The present invention aims to allow the realization of a simplified rotary switch whose breaking capacity is increased without significant modification of the device and this object is achieved by the implementation of the features of claim 1.

Document DE-B-1.199.363 describes a low voltage switch in which an arc drawn between two contacts is moved along two divergent arc horns towards an extinguishing chamber. In its intermediate part, one of the arc horns forms a half-loop around a permanent magnet. The magnetic field generated by the current flowing through this half-loop is added to the field of the magnet to blow the arc towards the end of the arc horn and towards the extinguishing chamber where the arc cools and goes out. The half-loop forms a boss which does not have the effect of masking the hot spot created by the bow root at the end of the bow horn.

In medium-voltage switches, natural arc extinction is used when the current crosses to zero to ensure breaking, preventing re-ignition of the arc. To limit the risks of re-striking an arc after the current has gone to zero, certain switches include devices for magnetic blowing of the arc, in particular by permanent magnets imposing a rotation of the arc. The rotation of the arc and its roots reduces the heating and ionization of the insulating gas as well as the presence of hot spots on the contacts, capable of emitting electrons by thermoelectronic emission. The switch according to the present invention also makes use of a permanent magnet for magnetic blowing of the root of the arc, but the breaking principle is different since it is based on the observation that an important element for the non re-ignition after the zero current has passed is to prevent the two hot spots on the two contacts from facing each other. By moving at least one of the roots of the arc to a hidden location, especially on the rear part of the contact far from the other contact, it is possible to avoid the emission of electrons in the zone of separation of the contacts.

The rotary knife switch can comprise two cuts in series and the inventive arc root migration system can be associated with each of said cuts or only with one of them. The contact with arc migration track having a hidden hot point can be the mobile contact, or the fixed contact, or both and the permanent magnet is advantageously housed inside the contact in the form of a stud, in particular cylindrical. The axis of the cylindrical contact pad (s) is perpendicular to the plane of deflection of the knife, and the migration path of the arc root is formed by the external periphery of the contact pad, this periphery possibly being the cylindrical surface of the pad or the periphery of one or more lateral sections of the stud. The displacement of the arc can be guided on the migration track by covering the adjacent parts of the contact pad with an insulating coating. The arc root and the point associated hot move along a curved trajectory and it is clear that when the root reaches the hidden location, diametrically opposite on the cylindrical stud at the point of arcing, this hidden location is masked by the contact stud at the for the other contact. The rotation of the knife in a predetermined direction can be used to introduce an asymmetry which favors one of the directions of rotation of the arc root. The direction of rotation is determined by the polarity of the permanent magnet and by the direction of the current at the given time. During one of the alternations of the current, the root moves on the migration track in a given direction, which reverses automatically at the next alternation. It will appear more clearly from the following detailed description that the choice of this direction of rotation can be used to promote either the speed of extinction of the arc or the breaking capacity of the switch. The invention is applicable to any type of contact, in particular to butted contacts or to clamp contacts more particularly described below. The switch can be of the multipolar type with a common envelope for all the poles or with an individual envelope. The insulating gas for filling the envelopes is a gas with high dielectric strength such as sulfur hexafluoride at atmospheric or compressed pressure. The envelope can be made of an insulating or conductive material and the control mechanism can be incorporated or be arranged outside this envelope.

According to an improvement of the invention, the migration path of the arc root is capped by a cover in the area of the hidden location to limit the propagation of the electrons emitted in this area. This hood determines with the migration path an arc penetration corridor confining the ionized gases and the metallic vapors.

• la figure 1 est une vue schématique partiellement en coupe d'un interrupteur multipolaire selon l'invention;
• la figure 2 est une coupe suivant la ligne II-II de la figure 1 représentant l'interrupteur en position fermé;
• la figure 3 est une vue analogue à celle de la figure 2 montrant l'interrupteur en cours d'ouverture;
• la figure 4 est une demi-coupe illustrant une variante de réalisation selon l'invention;
• la figure 5 est une vue de côté en coupe de l'interrupteur selon la figure 4;
• les figures 6 à 11 sont des vues analogues à la figure 2, illustrant différentes variantes de réalisation selon l'invention.

Other advantages and characteristics will emerge more clearly from the following description of different embodiments of the invention given by way of non-illustrative examples. limiting, and shown in the accompanying drawings in which:

• Figure 1 is a schematic view partially in section of a multipole switch according to the invention;
• Figure 2 is a section along line II-II of Figure 1 showing the switch in the closed position;
• Figure 3 is a view similar to that of Figure 2 showing the switch during opening;
• Figure 4 is a half-section illustrating an alternative embodiment according to the invention;
• Figure 5 is a sectional side view of the switch according to Figure 4;
• Figures 6 to 11 are views similar to Figure 2, illustrating different alternative embodiments according to the invention.

In the figures, a medium-voltage rotary switch comprises a sealed casing 10 ensuring the housing of the three poles R, S, T of the switch. The casing 10 can be common to the three RST poles and be metallic or made of insulating material. It can also be constituted by the association of three modules, each assigned to one of the poles or be a single envelope 10 subdivided into three compartments by internal partitions 12, as shown in Figure 1. The three poles R , S, T are identical and only one of them will be described in detail below. The sealed envelope 10 is filled with a gas with high dielectric strength such as sulfur hexafluoride under atmospheric pressure or in overpressure.

Each pole has two fixed contacts 14,16 arranged at the inner periphery of the casing 10 at diametrically opposite points and each fixed contact 14,16 is extended by a sealed passage 18,20 of the casing 10. The movable assembly of the switch is constituted by a control shaft 22, carrying a rotary knife 28 constituted by two contact blades 24,26 whose opposite ends 30 , 32 form movable contact clips cooperating with the fixed contacts 14, 16. In the closed position of the switch, shown in Figure 2, the knife 28 electrically connects the fixed contacts 14,16 and the opening of the switch is achieved by a rotation of the shaft 22 counterclockwise of a watch. The two fixed contacts 14,16 are identical and each is arranged in the form of a cylindrical stud with an axis parallel to the shaft 22. Inside the cylindrical stud 14,16 is housed a permanent magnet 34 coated by a conductive sheath 36 cylindrical in shape. Between the pole faces of the permanent magnet 34 with axial magnetization and the sheath 36 are inserted discs 38 of thin steel. In the closed position, the movable contact clamp 30,32 encloses the lower periphery of the cylindrical contact pad 14,16, the contact blades 24,26 being in contact with the lateral edges of this pad. The axial dimension of the cylindrical stud 14,16 is slightly greater than the spacing of the clamps formed by the blades 24,26 to obtain sufficient contact pressure. The upper part of the lateral edges of the contact 14, 16 is coated with an insulating material 40 preventing the migration of the arc on this part.

The field lines of the permanent magnet 34 are shown in broken lines on the pole S of FIG. 1 and it can be seen that these lines extend parallel to the cylindrical periphery 42 of the contact pad 14, 16. This periphery 42 constitutes a migration path of the arc root anchored on this contact 14,16. In the closed position of the switch, shown in Figure 2, the current flows through the sheath 36 of the contact pad 14,16 outside the permanent magnet 34 without risk of demagnetization of the latter. When the shaft 22 is opened by rotation, the knife 28 separates from the fixed contacts 14, 16, and two arcs 44, 46, electrically connected in series, are drawn respectively between the fixed contact 14 and the knife 28, and between the latter and the fixed contact 16. Under the action of the magnetic field of the permanent magnet 34, the arc roots 48.50 anchored on the fixed contacts 14.16 are blown and they migrate on the cylindrical periphery 42 forming a migration path of the arc root. The direction of rotation of the arc root 48.50 is determined by the polarity of the alternating current at the time of cutting, and in Figure 3 we see that the two arc roots 48.50 are blown towards a hidden location 52.54 diametrically opposite to the point where the arc arises opposite the knife 28. The hot spots associated with the arc roots 48.50 are thus transferred to hidden locations 52.54 and during natural extinction arcs 44,46, when the current crosses to zero, the optimal conditions for non-restriking are respected. Indeed, the thermoelectronic emission at the hot spot 52,54 does not take place opposite the knife 28, which prevents or limits the risks of re-striking of the arcs 44,46 during the appearance of the recovery voltage. The migration of the roots of the arc 48.50 naturally participates in the elongation of the arc and in its displacement in the gaseous insulating medium to favor, in the usual way, the breaking of the current. It can be seen in FIG. 3 that, when the polarity of the current is reversed at the time of the formation of the arcs 44,46, the arc roots 48,50 rotate in the opposite direction to come towards the crossings 18,20 in locations less distant and hidden from the knife 28 as the hidden locations 52,54. If the power cut does not occur at the first zero crossing of the current and it is necessary to wait for the end of the next alternation where the optimal conditions of presence, hot spots at the hidden locations 52,54 are found. Certain specific arrangements described below avoid this asymmetry.

In the following figures, which illustrate different variant embodiments, the same reference numbers designate elements similar or identical to those of FIGS. 1 to 3.

Referring to Figures 4 and 5 we see an alternative embodiment in which the fixed contact 14 comprises a insulating coating in particular made of epoxy resin 56 covering the cylindrical surface of the contact pad 14. The flat edges or surfaces of the contact pad 14 are however bare and they constitute the contact and migration surfaces of the arc root. The operation of the switch is not affected by this modification, the arc root anchored on the fixed contact 14 being blown by the magnetic field of the permanent magnet along the periphery of the side or edges of the stud contact 14 to a hidden point 58 which is not opposite the movable contact knife 28. In this variant, it is advantageous to use a permanent magnet 34 with radial magnetization. The contact blades 24, 26 have been extended to move the contact point in the direction of the enclosure 10 and to distance the current path from the magnet 34 while limiting the risks of demagnetization. This feature can be used on the other variants described.

In the switch according to FIG. 6, the pair of contacts 14, 28 is replaced by a sliding contact 60. The rotation in the opening direction of the knife 28 generates the appearance of a single arc 46 which is extinguished in the manner described above by migrating the arc root to a hidden location. The insertion of a single arc in the circuit to be interrupted limits the breaking capacity of the switch but the production of the latter is simplified.

The polarity of the permanent magnets 34 determines the direction of rotation of the arcs 44,46 and in the example described with reference to FIGS. 1 to 3, the extinction and the interruption of the current are favored for one of the alternations of the alternating current. In the variant shown in Figure 7, a asymmetry between the contacts 14,16 is introduced by choosing opposite polarities of the magnets 34 associated with these contacts 14,16 so that if one of the arcs, for example the arc 44 is blown towards the hidden location 52, at a given instant the other arc 46 is blown towards the hidden location 54 at the next alternation. Whatever the polarity of the alternation at the time of the opening of the contacts 14,16,28, one of the arcs 44,46 will be blown towards the hidden location favoring extinction. This avoids any delay in breaking the current but with a slight detriment to the extinguishing power of one of the arcs 44,46.

The arc root migration tracks are preferably associated with the fixed contacts 14, 16 in the manner described above, but it is clear that it would not be departing from the scope of the invention to associate these tracks with the mobile contacts 30.32 carried by the knife 28 (Figure 8). The inertia of the moving assembly is increased by the presence of the permanent magnets 34 but the operation, in particular the displacement of the arc roots towards hidden locations, which are not opposite the opposite contact, remains fully preserved. Only one of the contacts 30, 32 can moreover be equipped with an arc migration path, the other contact being a standard contact or a contact having the arc root migration path associated with the contacts. fixed. Any other combination is conceivable and more particularly that shown in FIG. 10 in which all of the contacts 14, 16, 30, 32 are equipped with a migration track and an associated permanent magnet. The choice of the directions of rotation of the arc roots is thus notably increased and this choice is made according to the desired performances.

By avoiding according to the invention that the hot spots are facing each other at the time of cutting, the risks of non-recovery are low but they can be further reduced by providing, according to a development of the invention, confinement of these hot spots. In the variant illustrated in FIG. 9, the general structure of which corresponds to that illustrated in FIGS. 2 and 3, a cover 62 surrounds the pads of fixed contacts 14,16 in the vicinity of the hidden location 52,54. The cover 62 defines a corridor of small width allowing the penetration of the arc root and its migration to the hidden location 52, 54, while confining the electrons emitted by the hot spots in a space remote from the contacts. Hood 62 can wrap the fixed contact 14, 16 leaving only a slot for penetration of the arc, or this cover 62 can be constituted by a simple screen arranged opposite the hot spots. It emerges from the preceding description, that the rotational movement of the knife 28 introduces a asymmetry favoring cutting for one of the alternations of the current. By moving the fixed contact pads 14,16 with respect to the bushings 18,20, as shown in Figure 11, to arrange the separation points of the contacts 14,28; 16,28 and the current supply points at the contact pads 14, 16 at diametrically opposite locations, this asymmetry is avoided and the hidden points are reached whatever the alternation of the current.

The invention is of course applicable to other types of switches and more particularly to a switch having an enclosure 10 or tank of the modular type or, a metal tank. The switch may also include grounding contacts carried by the casing 10 and cooperating with the knife 28 and the contacts 14, 16, 28 may be of the abutment type or of any other constitution.

Claims (11)

1. A medium voltage rotary switch with a sealed enclosure (10), whose internal periphery bears two diametrically opposed stationary contacts (14, 16), each stationary contact being capable of cooperating with a movable contact (30, 32) of a contact bridge to form a pair of contacts, said contact bridge in the form of a pivoting knife-blade (28) being supported by a rotary operating shaft (22), which can selectively occupy a closed position in which the two pairs of contacts (14, 30; 16, 32) are closed and an open position, characterized in that at least one of the contacts of one of said pairs comprises a migration track (42) of the root (48, 50) of an arc (44, 46), drawn when the pair of contacts opens, that this migration track (42) extends in the opposite direction from the other contact of the pair, to enable the arc root and the associated hot spot to move on said migration track (42) to a hidden location (52, 54; 58) where the two hot spots associated with the two arc roots are masked with respect to one another by the contact with the migration track (42) and are not facing and that a permanent magnet (34), securedly fixed to the contact with the migration track (42), is arranged to blow the arc root towards said hidden location (52, 54; 58) to favor arc extinction and current breaking.
2. The rotary switch according to claim 1, characterized in that in the plane of movement of the contact bridge (28), the plot of said migration track (42) is a curved trajectory and that the permanent magnet (34) is disposed inside said migration track (42) with field lines arranged to move the arc root on said trajectory.
3. The rotary switch according to claim 2, characterized in that the contact with the migration track (42) is in the form of a cylindrical stud whose axis is parallel to said rotating operating shaft (22) and that it comprises a cylindrical permanent magnet (34) housed inside a cylindrical conducting sheath (36) constituting the contact area of said migration track (42).
4. The rotary switch according to claim 3, characterized in that the migration track (42) is formed by the cylindrical surface of said sheath (36), which extends on the opposite side from the other contact of said pair, and that the flat surfaces of the sheath are at least partially covered by an insulating coating (40) to prevent striking of the arc on these flat surfaces.
5. The rotary switch according to claim 3, characterized in that the migration track (42) is formed by the periphery of the flat surfaces of the cylindrical sheath (36), and that the cylindrical surface is at least partially covered by an insulating coating (56).
6. The rotary switch according to any one of the above claims, characterized in that each pair of contacts (14, 30; 16, 32) comprises a contact (14, 16) equipped with a migration track (42) and a permanent blowout magnet (34) and that the polarities of the magnets are such that both the arcs (44, 46) are blown during the same current half-wave towards said respective hidden locations (52, 54).
7. The rotary switch according to one of the claims 1 to 5, characterized in that each pair of contacts (14, 30; 16, 32) comprises a contact equipped with a migration track (42) and a permanent blowout magnet (34) and that the polarities of the magnets are such that one of the arcs is blown towards said hidden location during one of the current half-waves and the other of the arcs during the opposite current half-wave.
8. The rotary switch according to any one of the above claims, characterized in that a cover (62) caps the migration track (42) in the area of said hidden location (52, 54), leaving a corridor for the arc to enter and move to this hidden location (52, 54).
9. The rotary switch according to any one of the above claims, characterized in that each of said contacts (14, 30; 16, 32) is equipped with a migration track (42) and a permanent magnet (34).
10. The rotary switch according to any one of the above claims, characterized in that one (14) of the contacts of a pair of contacts (14, 30; 16, 32) comprises a cylindrical permanent magnet (34) whose axis is perpendicular to the plane of movement of the contact bridge (28), housed inside a cylindrical conducting sheath and that the other contact (30) of said pair is arranged as a contact grip which in the closed position grips the edge of the two lateral faces of said cylindrical sheath (36).
11. The rotary switch according to one of the claims 1 to 6, characterized in that the fixing point and current input point to the contact with the migration track (42) is diametrically opposite from the separation point of the contacts (14, 30; 16, 32) where the arc (44, 46) forms.

Images