Title:
BLAST ORIFICE UNIT FOR SELF-BLASTING COMPRESSES GAS ELECTRIC CIRCUIT-BREAKERS
United States Patent 3670124
Abstract:
An axial blast breaking chamber for self-blasting compressed gas electric rcuit breakers wherein the chamber wall is solid and is provided with a plurality of internal longitudinal grooves extending parallel to and symmetrically disposed about the axis of the chamber. When the contacts are closed the fixed contact, which is in close-proximity to the inner wall of the chamber, extends past the grooves thereby inhibiting flow of quenching gas. Flow of quenching gas remains inhibited until the chamber and attached movable contact are displaced sufficiently to withdraw a portion of the longitudinal grooves below the lower end of the fixed contact.
US Patent References:
Orifice structure for compressed gas-circuit interrupter
Telford - December 1966 - 3291948
Orifice structure for compressed gas-circuit interrupter
Telford - December 1966 - 3291948
Application Number:
05/134268
Publication Date:
06/13/1972
Filing Date:
04/15/1971
View Patent Images:
Export Citation:
Assignee:
MAGRINI Fabbriche Riunite Magrini-Scarpa e Magnano M.S.M. S.p.A. (Milan, IT)
Primary Class:
Other Classes:
218/53
International Classes:
H01H33/70; H01H33/70
Field of Search:
200/148A,148R,148C
Primary Examiner:
Macon, Robert S.
Claims:
What is claimed is
1. In an axial blast breaking chamber for self-blasting compressed gas electric circuit breakers having fixed and movable contacts (30, 31), a blast orifice unit internally shaped to provide, in the outlet direction, a first conical and convergent zone (1), a second cylindrical zone (5) and a third substantially conical and divergent zone (9) having a length L equal to or greater than
2. An axial blast breaking chamber as defined by claim 1 wherein said chamber is provided with at least two longitudinal grooves (21).
3. An axial blast breaking chamber as defined by claim 1 wherein said chamber is provided with four longitudinal grooves (21).
4. An axial blast breaking chamber as defined by claim 1 wherein said longitudinal grooves (21) having one end within said second cylindrical zone (5) immediately adjacent the chamber cross-section separating said conical and convergent zone (1) from said cylindrical zone (5).
5. An axial blast breaking chamber as defined by claim 1 wherein said movable contact (31) is secured to said blast orifice unit and, when said circuit breaker is closed, the fixed contact (30) extends into said first conical and convergent zone (1), the outer surface of said fixed contact being in close proximity to the inner wall surface of said second cylindrical zone (5) thereby inhibiting flow of the quenching gas, said flow continuing to be inhibited until said movable contact and blast orifice unit are displaced sufficiently to withdraw a portion of said longitudinal grooves (21) below the lower end of said fixed contact.
1. In an axial blast breaking chamber for self-blasting compressed gas electric circuit breakers having fixed and movable contacts (30, 31), a blast orifice unit internally shaped to provide, in the outlet direction, a first conical and convergent zone (1), a second cylindrical zone (5) and a third substantially conical and divergent zone (9) having a length L equal to or greater than
2. An axial blast breaking chamber as defined by claim 1 wherein said chamber is provided with at least two longitudinal grooves (21).
3. An axial blast breaking chamber as defined by claim 1 wherein said chamber is provided with four longitudinal grooves (21).
4. An axial blast breaking chamber as defined by claim 1 wherein said longitudinal grooves (21) having one end within said second cylindrical zone (5) immediately adjacent the chamber cross-section separating said conical and convergent zone (1) from said cylindrical zone (5).
5. An axial blast breaking chamber as defined by claim 1 wherein said movable contact (31) is secured to said blast orifice unit and, when said circuit breaker is closed, the fixed contact (30) extends into said first conical and convergent zone (1), the outer surface of said fixed contact being in close proximity to the inner wall surface of said second cylindrical zone (5) thereby inhibiting flow of the quenching gas, said flow continuing to be inhibited until said movable contact and blast orifice unit are displaced sufficiently to withdraw a portion of said longitudinal grooves (21) below the lower end of said fixed contact.
Description:
The object of this invention is to provide an improved blast orifice unit for self-blasting compressed gas electric circuit-breakers, which provides substantial improvement in the performance of the breaking chambers employed in said circuit-breakers in comparison with known types. Compressed gas circuit-breakers are already well known and widely used in electric generating and distributing systems and well known are, in particular, the axial blast breaking chambers, used in these types of circuit-breakers, the shape of which has, in its various embodiments been determined through widely known principles.
Recently, the applicant has filed other patent applications (against one of them Italian Pat. No. 791,651 has been granted, while others are still pending, one of them under reference 24973-A/69) concerning axial blast breaking chambers for self-blasting compressed gas electric circuit-breakers having an orifice shape, provided with decompression holes and ring-like grooves, said holes and grooves being formed to favor the escape of both the gases developed by the decomposition of the material making up the breaking chambers themselves and the quenching gas, thus obtaining a concomitant flow of the first and latter mentioned gases, said breaking chambers having their downstream (or end) parts dependently relating to the circuit-breaker rated service voltage according to the experimental relation
(simplified form:
wherein L stands for the chamber end part length, stated in mm, and U n is the circuit-breaker rated service voltage expressed in kV.
It has been found, however, that known axial blast breaking chambers do not exhibit optimum performance with respect to the arc quenching gas exhaust and the protection of parts external to the chamber against the action of the arc.
An object of this invention is therefore to provide a breaking chamber for compressed gas electric circuit-breakers which is structurally improved in comparison with the known chambers and particularly in connection with the breaking chambers of similar type previously disclosed by the applicant.
A further object of this invention is to provide improvements in the breaking chambers of electric circuit-breakers whereby decompression in the orifice unit zone having the smallest cross section is favored thereby permitting the quenching gas to escape with particular ease.
A still further object of this invention is to provide an axial blast breaking chamber in which it is possible to reach the best obtainable flow concomitance of the decomposition gases and the quenching gas through the end (or downstream) part of the interruption chamber itself, consequently accelerating the outflow of the whole of said gases through the outlet orifice of the chamber and decreasing the whirl effects occurring in the total outflow.
Still another object is to provide a breaking chamber wherein the parts external to the same chamber are efficiently protected, particularly the insulating bakelized paper cylinder or other insulation sleeve externally wrapping the chamber, against the effects of the breaking electric arc.
These and other objects, which those skilled in the art can better deduce from the following detailed description, are profitably reached by an axial blast breaking chamber for self-blasting compressed gas electric circuit-breakers, said breaking chamber having a blast orifice unit internally shaped so as to provide, in the outlet direction, a first conical and convergent zone, a second cylindrical zone having the smallest cross-sectional area in comparison with the other internal zones, without (unlike the embodiments of the known art) side located decompression means, and a third substantially conical and divergent zone, the length of which is determined from the already known experimental relation
said third conical and divergent zone having a plurality of ring-like grooves each of which is substantially triangular sectioned within a plane passing through the chamber axis with open base towards the outlet orifice of the breaking chamber, said breaking chamber having a full, single-pieced solid wall, the inner side of which is provided with at least two longitudinal grooves parallel to and symmetrically disposed towards the chamber main axis, the longitudinal extent of said grooves covering most of the longitudinal extent of said second cylindrical zone and at least a part of the longitudinal extent of said third conical and divergent zone.
The breaking chamber, which is the object of this invention will be hereinafter more fully described with reference to the enclosed drawings, wherein
FIG. 1 schematically shows the longitudinal section, of the breaking chamber according to this invention, marked by broken line A--A on FIG. 2 i.e., along two different axial planes.
FIG. 2 schematically shows a plan view of the same breaking chamber, cross sectioned in correspondence with plane B--B of FIG. 1.
FIG. 3 illustrates the breaking chamber of FIGS. 1 and 2 with the breaker contacts in their closed position, and
FIG. 4 illustrates the breaking chamber with the contacts in the open position.
Referring to these figures, the improvement in the blast orifice unit of the breaking chamber for self-blasting compressed gas electric circuit-breakers, being the scope of this invention, consists in providing a chamber with the following features: substantial orifice shape according to the Venturi tube principle, with a second zone 5 (or necked zone with the smallest cross-section) cylindrically shaped and lacking the usual decompression holes which let said cylindrical smallest surfaced zone 5 communicate with the breaking chamber outer room; the improvement consisting in providing a plurality of parallel longitudinal grooves 21, stretching towards the breaking chamber axis and axially extending at least so much to at least partially cover the second smallest surfaced cylindrical zone 5 and at least partially the third conical and divergent zone 9, said grooves 21 being made in the inner wall of the end or downstream zone or part 9 of the breaking chamber, said part 9 setting up the third or truncated cone divergent zone of the breaking chamber and being structured with ring-like triangularly cross sectioned grooves.
Referring to FIGS. 3 and 4, the fixed contact 30 and movable contact 31 are shown positional within the blast orifice unit, movable contact 31 being secured to and moving with the said unit. When the circuit-breaker is closed, the fixed contact 30 occupies a large portion of the space within the breaking chamber; i.e., the whole third zone 9, the whole second zone 5, as well as a large (when not full) part of the first conical and convergent zone 1. In these static conditions, the quenching gaseous fluid has no means for circulating. When, however, the opening operation is started, and consequently the self-blasting takes place, the fixed contact 30, being in close proximity to the inner wall surface of cylindrical zone 5, even if not fully tight, substantially hampers the quenching gas outflow, except the neglectable quantities which can escape through the usual mechanical clearances due to the machining tolerances. As the opening operation continues, as shown in FIG. 4, fixed contact 30 no longer blocks the inlets of grooves 21. The quenching gas outflow is from this moment established and passes easily through the grooves 21. The exhaust section area, initially limited to the sum of all the sections of grooves 21, gradually increases the more the breaking chamber parts from the fixed contact, since always wider sections of truncated cone zone 9 become engaged by the outflow, said sections being substantially circular crown-shaped as determined inside by the above specified fixed contact 30, and outside by the inner wall surface of said third truncated cone zone 9 which comprises longitudinal grooves 21, the sections of which provide zones projecting from the above specified circular crown into the plane of the latter.
The example illustrated by the figures shows four grooves 21, reciprocally displaced by 90°, as this is the preferential solution. It is, however, to be noted that these grooves can be at least two and also more than four in number. (However, less than four grooves is not as satisfactory, since this substantially reduces the outflow section available at the beginning of the opening operation.)
Several remarkable results are attained in this way. First, good conveying of the gas flow through grooves 21 towards outlet orifice 2 of the breaking chamber is provided, said conveying minimizing, to the greatest possible extent, the whirl effects occurring in said end zone 9 of the breaking chamber. The quenching gas is in fact, at a first stage, conveyed through grooves 21 only, and afterwards expanded in the above said circular crown sections of third zone 9 in a direction parallel to axis Y--Y of the chamber. Thus, the quenching as more easily drags the decomposition gases in the same direction, as the resultants of these decomposition gases (because of the particular shape of the chamber downstream zone 9, provided with triangular shaped ring-like grooves 13) are already directed towards outlet orifice 2 of the breaking chamber. Now, although the particular shape of the breaking chamber end zone 9 is the subject of previous applicant's patents, it is seen that, in the same chamber, the sum of the effects reached through the present and the foregoing inventions permits the attainment, with regard to quicker and fuller arc quenching, of more effective results than are attainable by having separate and single recourse to the prior art solutions. A further advantage offered by the solution proposed by this invention consists of the superior protection granted to the cylinder, made of bakelized paper or other suitable insulating material, the section of which is referenced 20 on the figures. In fact, the complete lack of radial holes through the chamber wall assures that the gases (first of all the quenching gas), highly heated in consequence of contact with the arc, are prevented from contacting cylinder 20. This contributes to long life for the cylinder since it is not subjected to burning. Also, the cylinder may be assembled closer to the breaking chamber thereby allowing greater compactness and smaller dimensioning of the whole assembly.
Evidently modifications and alternatives can be brought to the invention, as hereinabove described, exemplified, illustrated and hereunder claimed, without getting out of the inventional meaning and the invention juridical protection limits. For example, as already specified above, the number of grooves 21, can be varied within the limitations imposed by the constructional technology of the breaking chamber. Also the sectional shape of said grooves can be modified (although the shape shown on FIG. 2 is preferred). In addition, the present invention permits optimum operation of the circuit-breaker whenever applied to breaking chambers of similar type within the known art.
Recently, the applicant has filed other patent applications (against one of them Italian Pat. No. 791,651 has been granted, while others are still pending, one of them under reference 24973-A/69) concerning axial blast breaking chambers for self-blasting compressed gas electric circuit-breakers having an orifice shape, provided with decompression holes and ring-like grooves, said holes and grooves being formed to favor the escape of both the gases developed by the decomposition of the material making up the breaking chambers themselves and the quenching gas, thus obtaining a concomitant flow of the first and latter mentioned gases, said breaking chambers having their downstream (or end) parts dependently relating to the circuit-breaker rated service voltage according to the experimental relation
(simplified form:
wherein L stands for the chamber end part length, stated in mm, and U n is the circuit-breaker rated service voltage expressed in kV.
It has been found, however, that known axial blast breaking chambers do not exhibit optimum performance with respect to the arc quenching gas exhaust and the protection of parts external to the chamber against the action of the arc.
An object of this invention is therefore to provide a breaking chamber for compressed gas electric circuit-breakers which is structurally improved in comparison with the known chambers and particularly in connection with the breaking chambers of similar type previously disclosed by the applicant.
A further object of this invention is to provide improvements in the breaking chambers of electric circuit-breakers whereby decompression in the orifice unit zone having the smallest cross section is favored thereby permitting the quenching gas to escape with particular ease.
A still further object of this invention is to provide an axial blast breaking chamber in which it is possible to reach the best obtainable flow concomitance of the decomposition gases and the quenching gas through the end (or downstream) part of the interruption chamber itself, consequently accelerating the outflow of the whole of said gases through the outlet orifice of the chamber and decreasing the whirl effects occurring in the total outflow.
Still another object is to provide a breaking chamber wherein the parts external to the same chamber are efficiently protected, particularly the insulating bakelized paper cylinder or other insulation sleeve externally wrapping the chamber, against the effects of the breaking electric arc.
These and other objects, which those skilled in the art can better deduce from the following detailed description, are profitably reached by an axial blast breaking chamber for self-blasting compressed gas electric circuit-breakers, said breaking chamber having a blast orifice unit internally shaped so as to provide, in the outlet direction, a first conical and convergent zone, a second cylindrical zone having the smallest cross-sectional area in comparison with the other internal zones, without (unlike the embodiments of the known art) side located decompression means, and a third substantially conical and divergent zone, the length of which is determined from the already known experimental relation
said third conical and divergent zone having a plurality of ring-like grooves each of which is substantially triangular sectioned within a plane passing through the chamber axis with open base towards the outlet orifice of the breaking chamber, said breaking chamber having a full, single-pieced solid wall, the inner side of which is provided with at least two longitudinal grooves parallel to and symmetrically disposed towards the chamber main axis, the longitudinal extent of said grooves covering most of the longitudinal extent of said second cylindrical zone and at least a part of the longitudinal extent of said third conical and divergent zone.
The breaking chamber, which is the object of this invention will be hereinafter more fully described with reference to the enclosed drawings, wherein
FIG. 1 schematically shows the longitudinal section, of the breaking chamber according to this invention, marked by broken line A--A on FIG. 2 i.e., along two different axial planes.
FIG. 2 schematically shows a plan view of the same breaking chamber, cross sectioned in correspondence with plane B--B of FIG. 1.
FIG. 3 illustrates the breaking chamber of FIGS. 1 and 2 with the breaker contacts in their closed position, and
FIG. 4 illustrates the breaking chamber with the contacts in the open position.
Referring to these figures, the improvement in the blast orifice unit of the breaking chamber for self-blasting compressed gas electric circuit-breakers, being the scope of this invention, consists in providing a chamber with the following features: substantial orifice shape according to the Venturi tube principle, with a second zone 5 (or necked zone with the smallest cross-section) cylindrically shaped and lacking the usual decompression holes which let said cylindrical smallest surfaced zone 5 communicate with the breaking chamber outer room; the improvement consisting in providing a plurality of parallel longitudinal grooves 21, stretching towards the breaking chamber axis and axially extending at least so much to at least partially cover the second smallest surfaced cylindrical zone 5 and at least partially the third conical and divergent zone 9, said grooves 21 being made in the inner wall of the end or downstream zone or part 9 of the breaking chamber, said part 9 setting up the third or truncated cone divergent zone of the breaking chamber and being structured with ring-like triangularly cross sectioned grooves.
Referring to FIGS. 3 and 4, the fixed contact 30 and movable contact 31 are shown positional within the blast orifice unit, movable contact 31 being secured to and moving with the said unit. When the circuit-breaker is closed, the fixed contact 30 occupies a large portion of the space within the breaking chamber; i.e., the whole third zone 9, the whole second zone 5, as well as a large (when not full) part of the first conical and convergent zone 1. In these static conditions, the quenching gaseous fluid has no means for circulating. When, however, the opening operation is started, and consequently the self-blasting takes place, the fixed contact 30, being in close proximity to the inner wall surface of cylindrical zone 5, even if not fully tight, substantially hampers the quenching gas outflow, except the neglectable quantities which can escape through the usual mechanical clearances due to the machining tolerances. As the opening operation continues, as shown in FIG. 4, fixed contact 30 no longer blocks the inlets of grooves 21. The quenching gas outflow is from this moment established and passes easily through the grooves 21. The exhaust section area, initially limited to the sum of all the sections of grooves 21, gradually increases the more the breaking chamber parts from the fixed contact, since always wider sections of truncated cone zone 9 become engaged by the outflow, said sections being substantially circular crown-shaped as determined inside by the above specified fixed contact 30, and outside by the inner wall surface of said third truncated cone zone 9 which comprises longitudinal grooves 21, the sections of which provide zones projecting from the above specified circular crown into the plane of the latter.
The example illustrated by the figures shows four grooves 21, reciprocally displaced by 90°, as this is the preferential solution. It is, however, to be noted that these grooves can be at least two and also more than four in number. (However, less than four grooves is not as satisfactory, since this substantially reduces the outflow section available at the beginning of the opening operation.)
Several remarkable results are attained in this way. First, good conveying of the gas flow through grooves 21 towards outlet orifice 2 of the breaking chamber is provided, said conveying minimizing, to the greatest possible extent, the whirl effects occurring in said end zone 9 of the breaking chamber. The quenching gas is in fact, at a first stage, conveyed through grooves 21 only, and afterwards expanded in the above said circular crown sections of third zone 9 in a direction parallel to axis Y--Y of the chamber. Thus, the quenching as more easily drags the decomposition gases in the same direction, as the resultants of these decomposition gases (because of the particular shape of the chamber downstream zone 9, provided with triangular shaped ring-like grooves 13) are already directed towards outlet orifice 2 of the breaking chamber. Now, although the particular shape of the breaking chamber end zone 9 is the subject of previous applicant's patents, it is seen that, in the same chamber, the sum of the effects reached through the present and the foregoing inventions permits the attainment, with regard to quicker and fuller arc quenching, of more effective results than are attainable by having separate and single recourse to the prior art solutions. A further advantage offered by the solution proposed by this invention consists of the superior protection granted to the cylinder, made of bakelized paper or other suitable insulating material, the section of which is referenced 20 on the figures. In fact, the complete lack of radial holes through the chamber wall assures that the gases (first of all the quenching gas), highly heated in consequence of contact with the arc, are prevented from contacting cylinder 20. This contributes to long life for the cylinder since it is not subjected to burning. Also, the cylinder may be assembled closer to the breaking chamber thereby allowing greater compactness and smaller dimensioning of the whole assembly.
Evidently modifications and alternatives can be brought to the invention, as hereinabove described, exemplified, illustrated and hereunder claimed, without getting out of the inventional meaning and the invention juridical protection limits. For example, as already specified above, the number of grooves 21, can be varied within the limitations imposed by the constructional technology of the breaking chamber. Also the sectional shape of said grooves can be modified (although the shape shown on FIG. 2 is preferred). In addition, the present invention permits optimum operation of the circuit-breaker whenever applied to breaking chambers of similar type within the known art.