The present invention relates to circuit breakers including molded case circuit breakers and earth leakage breakers, in particular to structures of current interrupting sections in the circuit breakers.
This type of circuit breakers as mentioned above is a double-break type circuit breaker that comprises first and second fixed contactors of a current interrupting section in parallel arrangement, a bridge type rotatably movable contactor that holds movable contacts on the ends of a U-shaped arm, opposing fixed contacts attached on the ends of the fixed contactors, and a grid type arc extinguishing device which is disposed opposing and in front of the movable contactor (for example Japanese Patent Publication (Kokai) No. 11-273536).
When the movable contactor 3 in this structure is opened, as shown in
The current interrupting section of double-break type as described above, however, has a problem in that abnormal dissipation of the fixed and movable contacts occurs with repeated current interruption as described below, causing poor contact performance between the fixed and movable contacts in a closed state. A mechanism in the abnormal dissipation of contacts will be described in
The current interrupting section of double-break type as shown in
Interruption of a heavy short circuit current in the current interruption section generally causes dissipation of the movable contacts 3a and 3b due to melting and evaporation in the surface region of the contacts by energy of the arc. When the beginning points of the arc 1 and arc 2 move away on the contact surface outwardly as shown in
Therefore, an object of the present invention is to provide an improved circuit breaker of a double-break type that suppresses the abnormal dissipation of contacts as shown in
Further objects and advantages of the invention will be apparent from the following description of the invention.
To attain the above objects, a circuit breaker of a double-break type according to the present invention comprises, in a contact mechanism of a current interrupting section of the circuit breaker, first and second fixed contactors arranged in parallel and a bridge type movable contactor that holds, on the ends of a U-shaped arm, movable contacts opposing fixed contacts attached on the ends of the fixed contactors, wherein a circuit breaker according to the first invention comprises a magnetic plate interposed in a middle region between two pairs of the fixed and movable contacts at both sides and extending along the path of a switching movement of the movable contactor (first aspect).
A circuit breaker of the second aspect of the present invention comprises partition walls of organic polymer material provided to stand along a path of the switching movement of the movable contactor, the partition walls sandwiching each pair of the fixed contact and the movable contact at both sides thereof, to form a narrow gap arc extinguishing space between the partition walls. The partition walls have the following variations as to constitution.
A circuit breaker comprising a current interrupting section as described above has the following effects. In a circuit breaker according to the first aspect, which comprises the magnetic plate interposed in a middle region between the two pairs of fixed and movable contacts at both sides and extending along a path of the switching movement of the movable contactor, the magnetic plate performs a function of a magnetic shield inhibiting interference between the magnetic fields of arcs generated between the pairs of the fixed and movable contactors. As a result, the repulsive electromagnetic force F separating the arcs as shown in
In a circuit breaker of the second aspect, the partition walls of organic polymer material are provided to sandwich each pair of the fixed and movable contacts at both sides thereof to function as narrow gap arc extinguishing plates and create a narrow gap arc extinguishing space between the partition walls. When the arcs develop between the fixed and movable contacts in the event of current interruption and extend towards the partition walls provided outside the arcs driven by the repulsive electromagnetic force F (
An arc extinguishing effect is additionally produced by a narrow gap current limiting effect that is brought about owing to the structure of the second aspect in which the partition walls of organic polymer material are provided sandwiching each pair of the fixed and movable contacts at both sides thereof to function as the narrow gap arc extinguishing plates and create a narrow gap arc extinguishing space between the partition walls. By combining these partition walls with a grid type arc extinguishing device and disposing in a current interrupting section, the arc extinguishing capability of a circuit breaker is greatly improved.
In the structure according to another aspect of the invention, the partition walls provided outside the pairs of fixed and movable contacts are composed of an organic polymer material that generates a greater amount of evaporating gas due to the heat of arcing and the partition wall provided inside the pairs of fixed and movable contacts is composed of an organic polymer material that generates a smaller amount of evaporating gas. This structure makes it possible that the repulsive electromagnetic force F acting on the arc between the fixed contact and the movable contact (
In the structure according to yet another aspect of the invention, the partition walls provided outside the pairs of fixed and movable contacts are thicker than the partition wall(s) provided inside the pairs of fixed and movable contacts. This structure allows the outer partition walls that evaporate larger amount of gas to prevent from early dissipation and loss of strength for an arc extinguishing plate. It also allows the partition walls to keep the narrow gap current limiting effect stable for a long time.
In the structure according to still another aspect of the invention, a distance between the pair of fixed and movable contacts and the partition wall provided outside the pair of fixed and movable contacts is smaller than a distance between the pair of fixed and movable contacts and the partition wall provided inside the pair of fixed and movable contacts. Due to this structure, the amount of gas, generated out of the partition wall and caused by exposure to the arc between the fixed contact and the movable contact in the event of current interruption, is larger in the evaporation from the outer partition wall that is nearer to the contacts than the evaporation from the inner partition wall. As a result, the gas flow that pushes the arc from outside to inside is dominant in the narrow gap arc extinguishing space. On the contrary, the electromagnetic force F (
The synergy effect allows the pushing back force of the gas to the arc and the repulsive electromagnetic force to separate the arcs each other to be canceled each other. Therefore, the abnormal dissipation (unbalanced dissipation) of the contacts caused by outward shift of the beginning point of the arc, is more effectively suppressed.
a) and 5(b) illustrate a structure and a function of the essential parts of the current interrupting section in Example 3 according to the invention, in which
a) and 7(b) illustrate a structure and a function of the essential parts of the current interrupting section in Example 5 according to the invention, in which
a) to 11(c) schematically show movements of the arc generated between the fixed and movable contacts in
Some preferred embodiments according to the invention will be described with reference to the accompanying drawings. In the drawings of embodiments, the parts corresponding to those in
Now, description will be first made on the structure and function of the invention referring to
In this structure as shown in
As a result, the beginning point of the arc generated between the fixed and movable contacts stays at the center of the contact surface as shown in
Next, description will be made on the structure and function of the invention referring to
When the arc 1 developed between the fixed contact 1a and the movable contact 3a, and the arc 2 developed between the fixed contact 2a and the movable contact 3b in the event of current interruption move away in the opposite directions by the repulsive electromagnetic force (
As a result, the arc 1 and arc 2 are pushed back to the centers of the contact surfaces against the repulsive electromagnetic forces between the arcs. Therefore, the abnormal or unbalanced dissipation is prevented in the fixed contacts 1a, 2a and the movable contacts 3a, 3b likewise in Example 1.
In the structure of this Example 2, a narrow gap arc extinguishing space is created around each pair of fixed and movable contacts by arranging three sheets of partition walls 7a, 7b, and 7c sandwiching each pair of fixed and movable contacts and standing at the center as shown in
a) and 5(b) show Example 3 that is further improved from Example 2 of the invention. Among the partition walls 7a, 7b, 7c composing the narrow gap partition wall assembly 7 and arranged at both sides and at a center in this Example 3, material of the partition walls 7a and 7b arranged at the both sides is an organic polymer material that is readily decomposed by the heat of arc and evaporates a large amount of gases, while the material of the partition wall 7c arranged at the center is an organic polymer material that evaporates a smaller amount of gases. These materials are used in the partition walls to form narrow gap arc extinguishing spaces between the partition walls. The organic polymer material evaporating a large amount of gases can be selected from polyacetal, poly(methyl methacrylate), and the like; and the organic polymer material evaporating a small amount of gases can be selected from polyamide, polyethylene, poly(fluoroethylene), and the like.
When the partition walls 7a, 7b, 7c are exposed to the arcs arc 1 and arc 2 developed between the fixed contacts 1a, 2a and the movable contacts 3a, 3b in the above-described structure as shown in
Thus, the beginning point of the arc is prevented from moving away towards the end of the contact surface and stays in the center of the contact surface as shown in the figure. Therefore, the abnormal or unbalanced dissipation of the contact is avoided, and with the additional arc extinguishing effect by the narrow gap arc extinguishing space formed between the partition walls, high circuit breaking performance is achieved.
Accordingly, the thicknesses t1 of the partition walls 7a and 7b disposed outside the pairs of fixed and movable contacts are made thicker than the thickness t2 of the inner partition wall 7c disposed in the middle position (t1>t2), thereby preventing the partition walls 7a and 7b that dissipate faster due to a larger amount of evaporating gas from lowering of strength. Therefore, the narrow gap current limiting effect in the event of current interruption is stably kept for a long time.
Next, the structure and function of Example 5 of the invention is described referring to
Regarding the three sheets of partition walls (made of an organic polymer material) 7a, 7b, 7c provided sandwiching the pair of fixed contact 1a and movable contact 3a and the pair of fixed contact 2a and movable contact 3b, and provided between the pairs of contacts, the distance d2 is shorter than the distance d1 (d2<d1), where d1 is the distance between the partition wall 7c in the middle (inside) and the pair of a fixed contact and a movable contact, and d2 is the distance between the partition wall 7a or 7b at both sides (outside) and the pair of a fixed contact and a movable contact (
Regarding the gas 1, gas 2, gas 3 evaporating from the surface of the partition walls 7a, 7b, 7c exposed to the arc 1 and arc 2 developed between the fixed and movable contacts in the event of current interruption in this structure, the amount of the gas 1 and gas 2 evaporating from the outer partition walls 7a, 7b, which are located at a shorter distance to the pair of fixed and movable contacts, is larger than the amount of gas 3 evaporating from the partition wall 7c disposed inside (
In the narrow gap arc extinguishing space formed between the partition walls, the flows of gas 1 and gas 2 evaporated from the outer partition walls 7a, 7b are generated to push the arc 1 and arc 2 developed between the fixed and movable contacts towards the central partition wall 7c. On the other hand, the repulsive electromagnetic force F (
The disclosure of Japanese Patent Applications No. 2006-318028 filed on Nov. 27, 2006 and 2006-067518 filed on Mar. 13, 2006 are incorporated as references.
While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.
Number | Date | Country | Kind |
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2006-067518 | Mar 2006 | JP | national |
2006-318028 | Nov 2006 | JP | national |
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Number | Date | Country | |
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20070210885 A1 | Sep 2007 | US |