Direct-current load-break switch particularly for traction lines

Abstract

 A direct-current load-break switch (1) particularly for traction lines, suitable for installations in a metallic cell, with two interruption segments in series, comprising:
two fixed contacts (5);
a double moving contact (8), which is adapted to engage and disengage with respect to the fixed contacts (5);
means for actuating the moving contact (8) which are adapted to move the moving contact (8) so that it engages and disengages the fixed contacts (5); each fixed contact (5) and the corresponding moving contact (8) are provided with an arc quenching horn (6, 10), and a coil provided with a magnetic core (12, 13) is connected electrically between the arc quenching horn (6, 10) (which is insulated) and the fixed contact; one or more arc quenching chambers are further arranged above the interruption segment formed by the arc quenching horns (6, 10).

Description

[0001] The present invention relates to a 750-1500-3000 V DC (referenced hereinafter as 3-kV) load-break switch (disconnector), particularly for traction lines. More particularly, the invention relates to a 3-kV traction line load-break switch adapted for mounting in a prefabricated metallic cell.

[0002] As is known, the opening/closing of the traction current and the disconnection of the contact line in 3-kV electric traction systems is generally performed by means of single-pole horn-type load-break switches mounted on poles outside a substation or along the line.

[0003] The horn-type load-break switch is composed of a power contact, which is capable of carrying the continuous current of the line, and an interruption contact, which is electrically in parallel to the power contact and has horn-shaped diverging electrodes which are adapted to elongate upwardly, until quenching occurs due to the combined effects of the magnetic field and of the temperature, the arc which forms between the electrodes when the contact opens.

[0004] During closure, the horn-shaped contact precedes the power contact; during opening, the power contact instead precedes the horn-shaped contact.

[0005] The open space in which the load-break switch is normally arranged and the natural replacement of the dielectric medium ensure cooling of the arc during elongation and deionization of the surrounding air at the end of the opening process. It should be noted that although mounting such disconnectors on a pole is advantageous in terms of disconnection visibility, it is disadvantageous for the transmission of movement and for maintenance.

[0006] If the disconnector is mounted in a closed cell, the conditions described above are no longer provided due to the confined nature of the available space.

[0007] It is also known that fault current opening, due to the high values of the short-circuit current ramp, is instead performed in switches which privilege swiftness of interruption so that it occurs before the steady-state value is reached. Current quenching is achieved by deflecting the arc, by magnetic blowing, from the contact to a quenching chamber where there are metallic segments which, by splitting the arc into a series of elementary arcs which are optionally configured in a spiral shape, cause its elongation and cooling until it is quenched.

[0008] The devices described above can be mounted in a closed cell as long as suitable vents are provided for the ionized gas in case of high-intensity short circuits.

[0009] The short duration of the interruption requires a reduced mass and stroke for the moving contact and therefore a limited dielectric strength when the contact is open, and therefore such devices are not adapted for disconnecting the line after interruption.

[0010] It is therefore necessary for the load-break switch being considered to minimize the ionization of the medium, i.e., the duration of the interruption process, by maintaining, when the disconnector is open, a distance between the contacts which ensures the required dielectric strength and, when the disconnector is closed, a surface of the contact which keeps the temperature within the allowed limits.

[0011] The aim of the present invention is to provide a direct-current load-break switch which has a performance, in terms of open contact dielectric strength, closed-contact continuous current, dynamic current, short-circuit closure current and transition times, which are similar or superior to those of conventional outdoor horn-type load-break switches, of known horn-type outdoor disconnectors.

[0012] Within this aim, an object of the present invention is to provide a load-break switch which has reduced arc energy and ionization, so as to make it compatible with installation in metallic cells arranged both indoors and outdoors and consequently does not require an operator to work at considerable heights for maintenance operations and also does not require a complex motion transmission system.

[0013] Another object of the present invention is to provide a load-break switch which allows to reduce the actuation energy involved.

[0014] Still another object of the present invention is to provide a load-break switch which is highly reliable, relatively simple to maintain and at sustainable costs.

[0015] This aim and these and other objects, which will become better apparent hereinafter, are achieved by a direct-current load-break switch with two interruption segments in series, comprising:

two fixed contacts;

a double moving contact, which is adapted to engage and disengage with respect to the fixed contacts;

means for actuating said double moving contact which are adapted to move said moving contact so that it engages and disengages said fixed contacts, characterized in that
each fixed contact and the corresponding moving contact are provided with an arc quenching horn, a coil provided with a magnetic core being connected electrically between the arc quenching horn (which is insulated) and the respective said fixed contact, one or more arc quenching chambers being arranged above the interruption segment formed by the arc quenching horns.

[0016] Further characteristics and advantages of the invention will become better apparent from the description of preferred but not exclusive embodiments of the load-break switch according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a transverse sectional view of the load-break switch according to the present invention;

Figure 2 is a top plan view (with some parts removed) of the disconnector according to the invention.

[0017] With reference to the figures, the load-break switch according to the invention, generally designated by the reference numeral 1, comprises two bars 2, which are supported by insulators 4, each bar ending with a fixed contact of the clamp type 5, an arc quenching horn 6 which is rigidly connected to the bar 2 but is insulated from it by means of an insulating element 7, and a double moving contact 8, which is rigidly coupled to an insulator 9 which connects it to an actuation mechanism. The moving contact 8 also is provided with arc quenching horns 10 with pusher springs 11 and with a horn extension 10a, both of which are connected electrically to the moving contact 8.

[0018] Two blowing coils with adapted magnetic cores 12 and 13 are each connected electrically to a bar 2 and to the corresponding fixed horn 6.

[0019] At least one and preferably two quenching chambers with metallic segments 14 and 16 are arranged respectively above each interruption portion; the chambers enclose the arc quenching horns 6 and 10 of the fixed and moving contacts, while the blowing coils with magnetic cores 12 and 13 are segregated by insulating walls.

[0020] Substantially, therefore, a dual simultaneous interruption with magnetic blowing is provided, since the two moving contacts are electrically and mechanically coupled.

[0021] The actuation mechanism of the disconnector is constituted by a guide 20, which is rigidly coupled to the fixed structure and on which a bridge 21 with the insulator 9 and the moving contact 8 slides with a linear motion.

[0022] Closure springs, designated by the reference numeral 22, are arranged between the ends of the guide 20 and the bridge 21, and opening springs 15 are arranged between the fixed structure and the bridge 21.

[0023] The opening springs 15 and the closure springs 22 are preloaded so that the generated force is scarcely dependent on the stroke.

[0024] The loading of the springs 15 and 11 is such as to accelerate the moving contact and complete the opening stroke in the required time.

[0025] Preloading of the springs 15 when the disconnector is open for an entire closure/opening cycle is performed by means of a gearmotor 30 and lever means 31. The gearmotor and the lever means are connected to a fixed footing 32, which is rigidly coupled to the insulators 4.

[0026] Operation of the load-break switch according to the invention is as follows.

[0027] When the disconnector is open, the activation of a closure electromagnet or of a detent, not shown, releases the spring 22, the bridge 21 and the moving contact 8.

[0028] The closure without rebounding of the horn contacts 10 with loading of the corresponding springs 11 precedes the insertion of the moving contact 8 in the clamps 5 of the fixed contact.

[0029] The closure movement of the moving contact occurs, looking for example at Figure 1, with a movement to the left of the moving contact 8, while opening occurs by way of a movement to the right of the moving contact 8.

[0030] When the disconnector is closed, the activation of an opening electromagnet or of a detent, not shown, releases the spring 15, which entrains the bridge 21 and the moving contact 8.

[0031] During the first part of the opening stroke, the metallic continuity of the circuit is maintained by means of the horn contact 10, the blowing coils 12 and 13 and the moving contact. The iron magnetic circuit therefore is the seat of a magnetic flux which is proportional to the line current which affects the arc quenching contacts and their extensions and partially affects the quenching chambers 14 and 16.

[0032] The radial component of this flux interacts with the current of the arc that forms after the opening of the horn contacts, pushing the arc along the expansions of the horns 6 and 10 toward the quenching chambers 14 and 16.

[0033] Within said chambers, which are spiral-shaped, the axial component of the field generated by the spiral and the axial component of the field produced by the coils are added together, accelerating the quenching of the arc and providing faster deionization of the medium, which thus occurs in a time which is comparable to that of an ultrafast switch.

[0034] The load-break switch according to the invention can therefore be used in a closed environment, such as a prefabricated metallic cell, since it is possible to quench the arc in a short time with reduced energy loss without requiring large spaces to contain the arc.

[0035] In practice it has been found that the load-break switch according to the invention fully achieves the intended aim and objects, since though maintaining test voltages at 50 Hz between the open contacts above 20 kV it can be installed within a closed structure instead of requiring open spaces like known kinds of horn-type disconnectors.

[0036] The load-break switch according to the invention in fact performs a double series interruption between the fixed contact and the moving contact, reducing the stroke of the moving contact for an equal insulation distance, to the benefit of the size of the apparatus and of its intervention times.

[0037] The load-break switch thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

[0038] All the details may further be replaced with other technically equivalent elements.

[0039] In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to requirements and to the state of the art.

[0040] The disclosures in Italian Patent Application no. MI2006A000421 from which this application claims priority, are incorporated herein by reference.

[0041] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A direct-current load-break switch particularly for traction lines, with two interruption segments in series, comprising:

two fixed contacts;

a double moving contact, which is adapted to engage and disengage with respect to said fixed contacts;

means for actuating said moving contact which are adapted to move said moving contact so that it engages and disengages said fixed contacts;

characterized in that
each fixed contact and the corresponding moving contact are provided with an arc quenching horn; a coil provided with a magnetic core being connected electrically between the arc quenching horn (which is insulated) and said fixed contact, one or more arc quenching chambers being further arranged above the interruption segment formed by the arc quenching horns.

2. The load-break switch according to claim 1, characterized in that it comprises a pair of bars, each provided at one end with one of said fixed contacts.

3. The load-break switch according to claim 1, characterized in that it comprises two electric arc quenching chambers.

4. The load-break switch according to one or more of the preceding claims, characterized in that the blowing coils are connected electrically between a bar and the corresponding arc quenching horn.

5. The load-break switch according to one or more of the preceding claims, characterized in that said bars are connected to a fixed footing by means of an insulating support.

6. The load-break switch according to one or more of the preceding claims, characterized in that it comprises a guide which is connected to said fixed footing on which said double moving contact slides, actuated by said actuation means of said moving contact.

7. The load-break switch according to one or more of the preceding claims, characterized in that said fixed contacts are of the clamp type.

8. The load-break switch according to one or more of the preceding claims, characterized in that it comprises springs for closing said moving contact onto said fixed contact and springs for opening said moving contact, said closure and opening springs being arranged around rods which are parallel to the guide of the moving contact.

9. The load-break switch according to one or more of the preceding claims, characterized in that it comprises a gearmotor and lever means for loading the opening springs when the disconnector is open.

10. The load-break switch according to one or more of the preceding claims, characterized in that said double moving contact is connected to said actuation means by means of an insulator.

11. The load-break switch according to one or more of the preceding claims, characterized in that said horns of said fixed contacts are connected mechanically to the corresponding bar by interposing insulating elements.

Drawing