1. Field of the Invention
This invention pertains generally to circuit interrupters and, more particularly, to calibration of circuit breakers including a thermal trip assembly. The invention also relates to methods of thermally calibrating circuit interrupters.
2. Background Information
Electrical switching apparatus, such as circuit interrupters, include an operating mechanism and a trip mechanism, such as a thermal trip assembly and/or a magnetic trip assembly. For example, the trip mechanism is automatically releasable to effect tripping operations and manually resettable following tripping operations.
Examples of circuit breakers including trip mechanisms are disclosed in U.S. Pat. Nos. 5,805,038 and 6,838,961, which are incorporated by reference herein. Such circuit breakers, commonly referred to as “miniature circuit breakers,” have been in use for many years and their design has been refined to provide an effective, reliable circuit breaker which can be easily and economically manufactured and tested. As such, the ease of test of such circuit breakers is of importance.
As is well known, circuit breakers of this type include, for example, at least one set of separable contacts disposed within a non-conductive housing. Typically, there is a fixed contact attached to the housing and a movable contact coupled to the operating mechanism. The operating mechanism includes a movable handle that extends outside of the housing. Movement of the separable contacts is accomplished by the operating mechanism. The operating mechanism typically includes components such as the previously mentioned handle, an operating arm, upon which the movable contact is disposed, a cradle, and the trip mechanism, such as the previously mentioned thermal trip assembly and/or magnetic trip assembly. The cradle is coupled to a spring and disposed between the trip mechanism and the operating arm. The components may further include a frame to which the other components are coupled.
Referring to
Typically, a circuit interrupter, such as the circuit breaker 2, which includes a thermal trip assembly such as bimetal assembly 22, prior to thermal calibration has a relatively high thermal response (i.e., it takes relatively longer to trip). Still referring to
For example, the starting angle 20 of the bimetal assembly 22 is, for example and without limitation, 8.7° before calibration. As the flat bit 12 enters the calibration slot 18 in the frame 16 and begins to turn clockwise (with respect to
In particular, the flat bit 12 deforms the upper right portion 24 of the frame 16 to the left (with respect to
When the circuit breaker 2 is closed, a persistent overload current of a predetermined value causes the bimetal 4 to become heated and deflect to the right (with respect to
There is room for improvement in methods of thermally calibrating circuit interrupters.
There is also room for improvement in circuit interrupter test systems.
These needs and others are met by embodiments of the invention, which provide for bi-directional adjustment of the circuit interrupter frame, in order to calibrate the thermal trip assembly for a subsequent thermal response, which is different than an initial thermal response, and to re-calibrate the thermal trip assembly for another thermal response, which is between the initial and subsequent thermal responses.
As one aspect of the invention, a method of thermally calibrating a circuit interrupter comprises: employing a circuit interrupter under test; including with the circuit interrupter under test a deformable frame having an elongated slot, an elongated deformable portion adjacent the elongated slot and a movable portion adjacent the elongated deformable portion; coupling a thermal trip assembly to the movable portion of the deformable frame; employing the thermal trip assembly having a first thermal response; straddling the elongated deformable portion of the deformable frame with a tool; rotating the tool in a first rotational direction and responsively deforming the elongated deformable portion and moving the movable portion of the deformable frame in a first direction, in order to calibrate the thermal trip assembly for a second thermal response, which is different than the first thermal response; and rotating the tool in a second rotational direction, which is opposite the first rotational direction, and responsively deforming the elongated deformable portion and moving the movable portion of the deformable frame in a second direction, which is opposite the first direction, in order to re-calibrate the thermal trip assembly for a third thermal response, which is between the first and second thermal responses.
The method may further comprise including with the elongated deformable portion a first side and an opposite second side; and employing as the tool a forked bit having a first fork member adjacent the first side of the elongated deformable portion and an opposite second fork member adjacent the opposite second side of the elongated deformable portion.
The method may also comprise employing as the opposite second side of the elongated deformable portion an outer edge of the deformable frame; disposing the elongated deformable portion between the elongated slot and the outer edge; disposing the first fork member in the elongated slot; and disposing the opposite second fork member adjacent the outer edge of the deformable frame.
As another aspect of the invention, a circuit interrupter test system comprises: a circuit interrupter under test, the circuit interrupter under test comprising: a deformable frame including an elongated slot, an elongated deformable portion adjacent the elongated slot and a movable portion adjacent the elongated deformable portion, and a thermal trip assembly coupled to the movable portion of the deformable frame; and a calibration device comprising: a tool straddling the elongated deformable portion of the deformable frame, wherein the thermal trip assembly has a first thermal response, wherein the calibration device is structured to rotate the tool in a first rotational direction and responsively deform the elongated deformable portion and move the movable portion of the deformable frame in a first direction, in order to calibrate the thermal trip assembly for a second thermal response, which is different than the first thermal response, and wherein the calibration device is structured to rotate the tool in a second rotational direction, which is opposite the first rotational direction, and responsively deform the elongated deformable portion and move the movable portion of the deformable frame in a second direction, which is opposite the first direction, in order to re-calibrate the thermal trip assembly for a third thermal response, which is between the first and second thermal responses.
The elongated deformable portion may include a first side and an opposite second side; and the tool may include a forked bit having a first fork member adjacent the first side of the elongated deformable portion and an opposite second fork member adjacent the opposite second side of the elongated deformable portion.
The opposite second side of the elongated deformable portion may be an outer edge of the deformable frame; the elongated deformable portion may be between the elongated slot and the outer edge; the first fork member may be in the elongated slot; and the opposite second fork member may be adjacent the outer edge.
The calibration device may further comprise a calibration apparatus structured to rotate the tool.
The opposite second side of the elongated deformable portion may be an outer edge; the thermal trip assembly may be a bimetal disposed at a first angle for the first thermal response; the second thermal response may correspond to a second angle, which is less than the first angle; and the third thermal response may correspond to a third angle, which is less than the first angle and greater than the second angle.
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “straddle” and variations thereof shall mean “astride” an object or “with a member on each side” of an object. For example and without limitation, the disclosed forked bit 40 includes a first fork member 54 on one side of an elongated deformable portion 42 and an opposite second fork member 56 on the opposite second side of the elongated deformable portion 42. Hence, the example forked bit 40 straddles the portion 42.
The invention is described in association with a single-pole circuit breaker including a thermal-magnetic trip assembly, although the invention is applicable to a wide range of circuit interrupters including any number of poles and at least a thermal trip assembly.
As shown in
It will be appreciated that clockwise rotation (with respect to
As a result of the frame deformation, the angle 20″ (
Rotating the forked calibration bit 40 in one or both directions and deforming the frame 16 in two opposite manners eliminates fall-out of certain circuit breakers after re-check, which would otherwise result from such circuit breakers being below the low end of the desired calibration range with no re-calibration being possible (as in
The elongated deformable portion 42 of the circuit breaker 2 includes a first side, which is the right side 30 of the slot 18, and an opposite second side 52. The forked bit 40 includes a first fork member 54 adjacent the right side 30 of the slot 18 and an opposite second fork member 56 adjacent the opposite second side 52 of the elongated deformable portion 42. The second side 52 of the elongated deformable portion 42 is an outer edge of the deformable frame 16. The elongated deformable portion 42 is between the elongated slot 18 and that outer edge 52. The first fork member 54 is in the elongated slot 18 and the opposite second fork member 56 is adjacent the outer edge 52.
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.