Patent Application
20080094155
The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:
a is a side view of a bimetal attached to the outside of a yoke through which two pigtail conductors are received according to an aspect of the present invention;
b is a side view of a retaining member in the yoke for securing the two pigtail conductors during a short circuit according to an aspect of the present invention; and
c is a side view of a bimetal attached to the outside of a yoke through which one pigtail conductor is received according to an aspect of the present invention.
Although the invention will be described in connection with certain preferred embodiments, it will be understood that the invention is not limited to those particular embodiments. On the contrary, the invention is intended to include all alternatives, modifications and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.
Referring now to the drawings and initially to
The bimetal 14 is mounted to the outermost surface of the yoke 16 such that the bimetal 14 is in a parallel relationship relative to the outside of the yoke 16. In other words, the bimetal 14 is mounted on the outside of the yoke such that the exterior planar surfaces of the bimetal 14 and the yoke 16 are adjacent to one another. The bimetal 14 is longer than the yoke 16 and extends along the length of the yoke 16 and beyond it. The bimetal 14 is positioned in a generally parallel relationship with the pigtail conductor 12 as it passes through the yoke 16. According to aspects of the present invention, the yoke includes a portion that is generally U-shaped, forming a U-shaped channel that receives a pigtail conductor. The ends of the U-shaped portion of the yoke forms two pole faces. According to other aspects of the present invention, the yoke includes a portion that is generally L-shaped, and the corresponding armature is also L-shaped. The end of the L-shaped portion of the yoke forms a single pole face.
The circuit breaker 10 is of the miniature type, which has an amperage rating of 10 A to 150 A. In various aspects, the width of the circuit breaker 10 may be one inch, ¾ inch, ½ inch, ⅜ inch, or less than ⅜ inch. Preferably, the length of the bimetal 14 exceeds that of the yoke 16, and the bimetal 14 extends along at least the entire length of the yoke 16. The length of the bimetals according to specific aspects of the present invention is about one and three-eighths of an inch. The width of the bimetals according to specific aspects of the present invention is about one eighth to about one quarter of one inch.
By mounting the bimetal 14 outside of the yoke 16, aspects of the present invention advantageously allow the overall width of the circuit breaker to be reduced without having to decrease the width or increase the thickness of the bimetal to attain a desired I2t performance. Any increase in the thickness in the bimetal will decrease its flexibility. Wider bimetals yield more consistent deflection movements and better force relationships among the tripping elements compared to narrower ones. The dimensions (width, thickness, length) of the bimetal 14 are optimized for both magnetic and thermal trip performance without altering the shape of the magnetic yoke size with the exception of its width. Indeed, if the circuit breaker width decreases, the width of the bimetal 14 does not need not be decreased and even its length can be increased, because there is more space available outside the yoke 16. In existing circuit breakers, the maximum width of the bimetal was constrained by the interior width of the yoke in which the bimetal was received. Increasing the bimetal length increases its overall effective travel distance, causing more rapid tripping. As the form factor of the circuit breaker decreases, there is less space to accommodate the components of the trip mechanism.
Another advantage to aspects of the present invention is that the current rating of the circuit breaker can be increased when a larger bimetal is installed outside of the yoke. The I2t capacity of the circuit breaker increases commensurate with the increase in the bimetal, resulting in a higher overall current rating.
Aspects of the present invention also advantageously allow the circuit breaker to meet a required I2t (current squared time) thermal capacity without having to sacrifice the cross-sectional area of the bimetal. Miniature circuit breakers in accordance with the present invention have performance and capacity characteristics that approach those of full-size circuit breakers. Additionally, mounting of the bimetal outside of the yoke provides more flexibility for optimizing the dimensions of the bimetal without being constrained by width and/or length dimensions of the circuit breaker in existing implementations.
By contrast, by mounting the bimetal outside of the yoke, aspects of the present invention do not suffer from the challenges faced by the prior-art arrangements where the circuit breaker's width is to be reduced. As compared to implementations where the bimetal is received inside the yoke, aspects of the present invention can easily maintain the same bimetal width even as the circuit breaker's width is reduced. Optimization of the bimetal's width, length, and thickness for both magnetic and thermal trip requirements is significantly improved according to aspects of the present invention.
For higher induced magnetic fields, it is known to wind the pigtail conductor around the magnetic yoke a number of turns commensurate with the desired increase in magnetic field. However, because the bimetal according to aspects of the present invention is mounted to the exterior of the yoke where the pigtail winding would otherwise be located, a different solution for achieving a higher magnetic field is needed.
A similar arrangement to
a-5c are side views of yoke and bimetal arrangements according to various aspects of the present invention. In
b illustrates a different way of attaching a second pigtail conductor 607 to the bimetal 602. The second pigtail conductor 607 is attached to the bimetal 602 in the manner shown to form a loop 609 before the second pigtail conductor 607 enters the yoke 600. The loop 609 forms a smoother transitional path for the current passing through the bimetal 602 as it transitions to the second pigtail conductor 607, helping to prevent the blow-apart effect caused by currents in the pigtail conductors 604, 607 on the hand and opposite-running currents in the bimetal 602 on the other hand. The opposite-running current in the bimetal 602 tends to direct the pigtail conductors 604, 607 away from the bimetal 602. A retaining member 618 holds the pigtail conductors 604, 607 in place relative to the yoke 600 during overcurrents, and prevents them from being blown away from the bimetal 602 due to the opposite-running current in the bimetal 602. By comparison, in
c illustrates an arrangement in which one pigtail conductor 604 is passed through the yoke 600, like that shown in
Additional aspects to the present invention relate to the methods by which the pigtail conductor(s) are assembled with the circuit breaker. In
While particular embodiments, aspects, and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.
