ADJUSTABLE THERMAL TRIP MECHANISM FOR CIRCUIT BREAKER

Abstract

An adjustable thermal trip mechanism for a circuit breaker is provided which can improve the reliability of over-current tripping by minimizing an influence upon thermal tripping even if an assembly error such as skewing or twisting occurs during assembly of bimetallic strips. The adjustable thermal trip mechanism for the circuit breaker comprises: a crossbar that is rotatable and has at least one power receiving portion for receiving rotary power; a bimetallic strip that can bend towards the power receiving portion when an over current occurs on the circuit; and an adjustment screw installed to face the power receiving portion, wherein the power receiving portion comprises a plurality of planar portions which are at different distances from the adjustment screw.

Claims

1. An adjustable thermal trip mechanism for a circuit breaker, comprising: a crossbar that is rotatable and has at least one power receiving portion for receiving rotary power; a bimetallic strip that can bend towards the power receiving portion when an over current occurs on the circuit; and an adjustment screw installed to face the power receiving portion, wherein the power receiving portion comprises a plurality of planar portions which are at different distances from the adjustment screw.

2. The adjustable thermal trip mechanism of claim 1, wherein the planar portions are configured to have steps-like configuration.

3. The adjustable thermal trip mechanism of claim 1, wherein the plurality of planar portions comprise: a first planar portion spaced a first distance apart from the adjustment screw, corresponding to a minimum value of reference current for over-current tripping; a second planar portion spaced a second distance, longer than the first distance, apart from the adjustment screw, corresponding to a medium value of reference current for over-current tripping; and a third planar portion spaced a third distance, longer than the second distance, apart from the adjustment screw, corresponding to a maximum value of reference current for over-current tripping.

4. The adjustable thermal trip mechanism of claim 1, wherein the plurality of planar portions are configured to have different lengths.

5. The adjustable thermal trip mechanism of claim 1, wherein the crossbar is coupled to an adjustment dial so that the horizontal position of the power receiving portion is moved in interlocking with the rotation of the adjustment dial, thereby changing the distance from the adjustment screw.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of the invention.

[0065] In the drawings:

[0066] FIG. 1 is a perspective view of the outward appearance of a molded-case circuit breaker to which conventional art or this invention can be applied and an enlarged view of an adjustment dial in the circle;

[0067] FIG. 2 is a perspective view from a terminal side, illustrating only the adjustment dial, crossbar, and thermal trip mechanism in the circuit breaker to which the conventional art and the present invention can be applied;

[0068] FIG. 3 is a perspective view obliquely viewing down from above a heater, illustrating only the adjustment dial, crossbar, and thermal trip mechanism in the circuit breaker to which the conventional art and the present invention can be applied;

[0069] FIG. 4 is a vertical cross-sectional view illustrating only the crossbar and thermal trip mechanism in the circuit breaker to which the conventional art and the present invention can be applied;

[0070] FIG. 5 is a perspective view showing the configuration of the crossbar of the thermal trip mechanism according to the conventional art;

[0071] FIG. 6 is a setting status view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to minimum by turning the adjustment dial of the thermal trip mechanism according to the conventional art;

[0072] FIG. 7 is a setting status view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to medium by turning the adjustment dial of the thermal trip mechanism according to the conventional art;

[0073] FIG. 8 is a view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to maximum by turning the adjustment dial of the thermal trip mechanism according to the conventional art;

[0074] FIG. 9 is a front view of a bimetal strip and a heater in the thermal trip mechanism, when the bimetal strip is skewed or twisted;

[0075] FIG. 10 is a perspective view showing the configuration of a crossbar in a thermal trip mechanism according to an exemplary embodiment of the present invention;

[0076] FIG. 11 is a setting status view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to minimum by turning the adjustment dial of the thermal trip mechanism according to the present invention;

[0077] FIG. 12 is a setting status view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to medium by turning the adjustment dial of the thermal trip mechanism according to the present invention; and

[0078] FIG. 13 is a setting status view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to maximum by turning the adjustment dial of the thermal trip mechanism according to the present invention;

DETAILED DESCRIPTION OF THE INVENTION

[0079] The above-described aspects of the present invention, the configuration of for accomplishing them, and its operational effects will be understood more clearly by the following description of an exemplary embodiment of the present invention with reference to the accompanying drawings.

[0080] FIG. 10 is a perspective view showing the configuration of a crossbar in a thermal trip mechanism according to an exemplary embodiment of the present invention. FIG. 11 is a view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to minimum by turning the adjustment dial of the thermal trip mechanism according to the present invention. FIG. 12 is a view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to medium by turning the adjustment dial of the thermal trip mechanism according to the present invention. FIG. 13 is a view showing the relative positions of the adjustment screw and crossbar and a shift in the position of the crossbar, when the distance between the adjustment screw and the crossbar is set to maximum by turning the adjustment dial of the thermal trip mechanism according to the present invention.

[0081] As illustrated in the figures, an adjustable thermal trip mechanism for a circuit breaker according to an exemplary embodiment of the present invention comprises a crossbar 20-1, bimetal strips 22, and adjustment screws 23.

[0082] In addition to these components, the adjustable thermal trip mechanism according to the present invention may further comprise the adjustment dial and heaters shown and described in FIGS. 1 to 9. Other components like terminals included in a molded-case circuit breaker are the same as those shown and described in the description of the background art, so redundant explanations or explanations will be omitted.

[0083] Referring to FIG. 10, the crossbar 20-1 is rotatable, and has dial connecting protrusions 20-1a and at least one power receiving portion (three power receiving portions in the embodiment shown in FIG. 10) 20-1b for receiving rotary power.

[0084] It is assumed that, in each of the three power receiving portions 20-1b, the side facing the adjustment screw 23 is the front side, and the opposite side is the rear side. Referring to FIG. 10, a plurality of planar portions 20-1b1, 20-1b2, and 20-1b3 are formed in such a manner that the distance from the rear side to the first planar portion 20-1b1 is a third distance T3, which is the longest distance, the distance from the rear side to the second planar portion 20-1b2 is a second distance T2, which is shorter than the third distance T3, and the distance from the rear side to the third planar portion 20-1b3 is a first distance T1, which is shorter than the second distance T2.

[0085] Referring to FIGS. 11 to 13, each of the power receiving portions 20-1b comprises a plurality of planar portions 20-1b1, 20-1b2, and 20-1b3 which are at different distances from the adjustment screw 23.

[0086] Among the planar portions 20-1b1, 20-1b2, and 20-1b3, the first planar portion 20-1b1 is spaced a first distance G1 apart from the adjustment screw 23, corresponding to the minimum setting value of reference current for over-current tripping. Among the planar portions 20-1b1, 20-1b2, and 20-1b3, the second planar portion 20-1b2 is spaced a second distance G2, longer than the first distance G1, apart from the adjustment screw 23, corresponding to the medium setting value of reference current for over-current tripping.

[0087] Among the planar portions 20-1b1, 20-1b2, and 20-1b3, the third planar portion 20-1b3 is spaced a third distance G3, longer than the second distance G2, apart from the adjustment screw 23, corresponding to the maximum setting value of reference current for over-current tripping.

[0088] Referring to FIG. 10, according to an exemplary embodiment of the present invention, the distances G1, G2, and G3 from the adjustment screw 23 to the planar portions 20-1b1, 20-1b2, and 20-1b3 form a step-like configuration throughout the lengths I1, I2, and I3, from a starting point to the terminal point.

[0089] In another exemplary embodiment of the present invention, the length I2 of the second planar portion 20-1b2 is longer than the length of the first planar portion 20-1b1 and the length I3 of the third planar portion I3. That is, I2>I1, and I2>I3.

[0090] In another exemplary embodiment, the length I2 of the second planar portion 20-1b2 is the longest, the length I3 of the third planar portion 20-1b3 is the middle, and the length I1 of the first planar portion 201b-1 is the shortest. That is, I2>I3>I1.

[0091] The bimetallic strips 22 are elements that can bend towards the power receiving portions 20-1 b when over-current occurs to the circuit.

[0092] As described with reference to FIG. 4, the bimetallic strip 22 can be attached tightly to the heater 24 and the upper part can bend freely towards the crossbar 20-1 with a predetermined distance from the heater 24.

[0093] As described with reference to FIG. 9, the bimetallic strip 22 can be fixed such that the lower part is attached tightly to the heater 24 by a pair of rivets R.

[0094] The bimetallic strip 22 is thermally expanded when the heater 24 attached tightly to the lower part is heated by over-current on the circuit, and this allows the upper part, which is a free end, to bend towards the crossbar 20-1.

[0095] The bimetallic strip 22 may include a threaded hole portion at the upper end to mesh the adjustment screw 23 with the threaded hole portion.

[0096] The adjustment screw 23 is installed at the upper part of the bimetallic strip 22 so as to be movable back and forth, facing the power receiving portion 20-1b of the crossbar 20-1.

[0097] The adjustment screw 23 is an element for rotating the crossbar 20-1 by pushing the power receiving portion 20-1b when the bimetallic strip 22 bends.

[0098] The operation of the adjustable thermal trip mechanism for the circuit breaker according to an exemplary embodiment of the present invention having the above-described configuration will be described with reference to FIGS. 10 to 13.

[0099] First of all, when the user uses a screwdriver to turn the adjustment dial 10 to the MIN position in the circle of FIG. 1 to set the rated current to minimum, the crossbar 20-1 connected to the adjustment dial 10 through the dial connecting protrusions 20-1a is moved to the farthest left, as shown in FIG. 11.

[0100] As such, the leading ends of the three adjustment screws 23 face the first planar portions 20-1b1 of the crossbar 20-1, respectively. Hence, the leading ends of the adjustment screws 23 and the first planar portions 20-1b1 of the crossbar 20-1 are at a first distance G1 which is the minimum distance from each other.

[0101] In this case, even if an assembly error such as skewing or twisting occurs during assembly of the bimetallic strips 22, the influence on the thermal tripping can be prevented without any change in the first distance G1, as long as the error is within the length of the first planar portions 20-1b1, thereby improving the reliability of over-current tripping.

[0102] Accordingly, the thermal trip mechanism according to the exemplary embodiment of the present invention works such that, when the current flowing through the circuit is at the minimum rated current, the leading ends of the adjustment screws 23 push the first planar portions 20-1b1 of the crossbar 20-1 to rotate the crossbar 20-1. In interlocking with this, the switching mechanism operates in the trip position (to automatically break the circuit).

[0103] In other words, the thermal trip mechanism according to present invention trips most sensitively at the minimum rated current.

[0104] Next, when the user uses a screwdriver to turn the adjustment dial 10 to the MED position in the circle of FIG. 1 to set the rated current to medium, the crossbar 20-1 connected to the adjustment dial 10 through the dial connecting protrusions 20-1a is moved a certain distance to the right from the position shown in FIG. 11, as shown in FIG. 12.

[0105] As such, the leading ends of the three adjustment screws 23 face the second planar portions 20-1b2 of the crossbar 20-1, respectively. Hence, the distances between the leading ends of the adjustment screws 23 and the second planar portions 20-1b2 of the crossbar 20-1 are a second distance G2 which is the medium distance from each other. And the second distance G2 is longer than the first distance G1 and shorter than a third distance G3 to be described later.

[0106] In this case, even if an assembly error such as skewing or twisting occurs during assembly of the bimetallic strips 22, the influence on thermal tripping can be prevented without any change in the second distance G2, as long as the error is within the length of the second planar portions 20-1b2, thereby improving the reliability of over-current tripping.

[0107] Accordingly, the thermal trip mechanism according to the exemplary embodiment of the present invention works such that, when the current flowing through the circuit reach the medium rated current, the leading ends of the adjustment screws 23 push the second planar portions 20-1b2 of the crossbar 20-1 to rotate the crossbar 20-1. In interlocking with this, the switching mechanism operates in the trip position (to automatically break the circuit).

[0108] In other words, the thermal trip mechanism according to the exemplary embodiment of the present invention trips at the medium rated current.

[0109] Next, when the user uses a screwdriver to turn the adjustment dial 10 to the MAX position in the circle of FIG. 1 to set the rated current to maximum, the crossbar 20-1 connected to the adjustment dial 10 through the dial connecting protrusions 20-1 a is moved a certain distance further to the right from the position shown in FIG. 12, as shown in FIG. 13.

[0110] As such, the leading ends of the three adjustment screws 23 face the third planar portions 20-1b3 of the crossbar 20-1, respectively. Hence, the distance between the leading ends of the adjustment screws 23 and the third planar portions 20b-2 of the crossbar 20-1 are a third distance G3 which the maximum distance from each other And the third distance G3 is longer than the second distance G2.

[0111] In this case, even if an assembly error such as skewing or twisting occurs during assembly of the bimetallic strips 22, the influence upon thermal tripping can be prevented as there is no change in the third distance G3, as long as the error is within the length of the third planar portions 20-1b3, thereby improving the reliability of over-current tripping.

[0112] Accordingly, the thermal trip mechanism according to the exemplary embodiment of the present invention works such that, when the current flowing through the circuit is at the maximum rated current, the leading ends of the adjustment screws 23 push the third planar portions 20-1b3 of the crossbar 20-1 to rotate the crossbar 20-1. In interlocking with this, the switching mechanism operates to the trip position (to automatically break the circuit).

[0113] In other words, the thermal trip mechanism according to the exemplary embodiment of the present invention trips at the maximum rated current.

[0114] As described above, in the adjustable thermal trip mechanism for the circuit breaker according to the present invention, each power receiving portion of the crossbar comprises a plurality of planar portions which are at different distances from the adjustment screw. Thus, even if an assembly error such as skewing or twisting occurs during assembly of the bimetal strips, the influence upon thermal tripping can be prevented, as long as the error is within the length of each planar portion. Therefore, the reliability of over-current tripping can be improved.

[0115] In the adjustable thermal trip mechanism for the circuit breaker according to the present invention, the planar portions form a step-like configuration. Thus, even if an assembly error such as skewing or twisting occurs during assembly of the bimetal strips, the influence upon thermal tripping can be prevented, as long as the error is within the area of the same stepped portion. Therefore, the reliability of over-current tripping can be improved.

[0116] In the adjustable thermal trip mechanism for the circuit breaker according to the present invention, the plurality of planar portions comprise a first planar portion spaced a first distance apart from the adjustment screw, a second planar portion spaced a second distance, longer than the first distance, apart from the adjustment screw, and a third planar portion spaced a third distance, longer than the second distance, apart from the adjustment screw. Thus, over-current tripping can be performed, corresponding to the maximum, medium, and minimum values of reference current for over-current tripping. Thus, even if an assembly error such as skewing or twisting occurs during assembly of the bimetal strips, the influence upon thermal tripping can be prevented, as long as the error is within the lengths of the first, second, and third planar portions, since there are no changes in the first, second, and third distances. Therefore, the reliability of over-current tripping can be improved.

[0117] In the adjustable thermal trip mechanism for the circuit breaker according to the present invention, the plurality of planar portions have different lengths, especially the second planar portion has the longest length. Thus, setting the rated current to the medium value of reference current for over-current tripping can widen the area where there is no change in the second distance even if an assembly error such as skewing or twisting occurs during assembly of the bimetal strips. Therefore, the influence upon thermal tripping can be prevented, and the reliability of over-current tripping can be improved.

[0118] In the adjustable thermal trip mechanism for the circuit breaker according to the present invention, the crossbar is coupled to the adjustment dial. Thus, the horizontal position of the power receiving portions can be moved in interlocking with the rotation of the adjustment dial, thereby changing the distance from the adjustment screw.