Patent Grant
7336146
This invention relates to a circuit breaker mechanism. In particular, the invention relates to the arrangement of a contact carrier forming part of the mechanism.
The conduction path of a circuit breaker typically includes a line terminal and a load terminal, with a set of contacts and a load sensing device between the contacts. Conventionally, the set of contacts comprises a fixed contact and a moving contact, with the moving contact being mounted on a contact carrier which is supported pivotably on a frame member of the mechanism. In known miniature circuit breakers, the contact carrier is mounted pivotably to an operating handle which in turn is supported pivotably on a handle frame of the circuit breaker mechanism. The handle frame also serves as part of the conduction path of the mechanism. A flexible conductor, known as a pig-tail, is welded to the moving contact carrier and to the handle frame and flexes with the movement of the contact carrier between a first position in which the contacts are closed and a second position in which the contacts are open.
The flexible pig-tail is typically welded to the contact carrier and the handle frame. The welding process can cause distortion of the contact carrier, resulting in the contact carrier rubbing on the shell or housing of the circuit breaker, negatively affecting the switching action of the mechanism. It will also be appreciated that the stiffness, the orientation and the length of the flexible pig-tail have a direct effect on the contact pressure and other operating characteristics of the circuit breaker mechanism.
It is an object of invention to provide a circuit breaker mechanism which reduces or does away with the need for a flexible conductor or pig-tail of the kind described above.
According to the invention there is provided a circuit breaker mechanism comprising a first terminal, a second terminal, a fixed contact connected to the first terminal, a conductive frame arranged to support an operating handle of the circuit breaker and connected electrically to the second terminal, and a moving contact assembly including a moving contact arranged to make contact with the fixed contact and a contact carrier supported pivotably on the conductive frame and connected both electrically and mechanically to said conductive frame only via a conductive pivot pin.
Typically, the first terminal is a line terminal and the second terminal is a load terminal.
The contact carrier preferably comprises a conductive member, the moving contact being supported at or near a first end of the conductive member and an opposed second end of the conductive member being shaped to engage at least one conductive pivot pin connected electrically to the conductive frame.
In a preferred embodiment of the invention, the conductive member comprises a pair of generally parallel elongate limbs connected together, the moving contact being supported at or near a first end of the conductive member and the ends of the limbs at an opposed second end of the conductive member having recesses formed therein to engage respective conductive pivot pins connected electrically to the conductive frame.
The mechanism may include a conductive bracket fixed to the conductive frame, the conductive bracket defining a pair of conductive pivot pins arranged to engage the respective ends of the limbs of the contact carrier.
The conductive bracket preferably comprises copper.
The conductive bracket may support a conductive handle pivot pin to which an operating handle of the mechanism is mounted, and which connects the conductive bracket electrically to the conductive frame.
The conductive handle pivot pin is preferably formed from copper.
The mechanism preferably includes at least one spring, which may be the main spring of the mechanism, arranged to urge the contact carrier of the moving contact assembly against said at least one conductive pivot pin.
The electrical conduction path of the circuit breaker mechanism of
The circuit breaker mechanism of the invention is illustrated in
The arrangement of the line terminal 10 and the fixed contact 12 are the same as in the mechanism of
The bracket 46 is preferably formed from copper of adequate hardness, plated with tin or silver, for example, to enhance its conductivity and provide suitable mechanical properties. The pins 40 and 42 can be formed integrally with the copper bracket, as shown, or could be brazed or otherwise fixed to the lower end of the bracket. In the latter case the pins could be formed of brass or bronze. The pins are preferably also plated with tin or silver.
The pins 40 and 42 define smoothly curved bearing surfaces on which the recesses 36 and 38 at the upper end of the contact carrier 16 pivot.
As best seen in
Welded to the end of the handle frame 26 remote from the bracket 46 is one end of a load sensing coil 54, the other end of which is welded to a load terminal 56. The current conduction path of the mechanism of
In order to ensure good contact between the upper end of the moving contact carrier 16 and the pins 40 and 42 of the bracket 46, the main spring 58 of the mechanism (shown schematically in
In a prototype version of the described mechanism, rated at 63A, a moderate temperature increase of the order of 10 degrees C. was noted in use at the rated load, compared with a conventional mechanism. However, the temperature at the load and line terminals remained substantially unchanged. If the temperature rise should be considered objectionable, the use of a copper top frame would assist in heat dissipation. It is also possible to use a pig-tail in addition to the described pivoting contact arrangement. In such a case a pig-tail can be smaller and lighter than in the case of the described prior art circuit breakers, for a given rating.
The main advantage of the described circuit breaker mechanism is that a consistent contact pressure can be maintained due to the absence of the pig-tail and any variations in the geometry of the contact carrier and other unwanted effects caused by the pig-tail. A softer main spring can be used as the variation in contact pressure and operating characteristics of the mechanism due to variations in the pig-tail characteristics is eliminated.
The described mechanism has an improved switching action due to the fact that the movement of the moving contacts is not impeded by the pig-tail, resulting in higher contact closing/opening speeds, and also by the fact that deformation of the moving contact carrier due to welding is eliminated and thus the moving contact carrier does not tend to rub on the frame or shell of the circuit breaker. Similarly, “stickiness” of the operating handle is avoided. Another advantage is that the elimination of the pig-tail allows the line terminal to be reshaped to form a closer loop with the contact carrier, improving blow-off during short circuit conditions, with a potential improvement in short circuit performance. The arrangement also provides for additional space for levers operating an “in-line trip alarm/auxiliary switch” mechanism. Finally, construction is simplified due to the absence of the welded pig-tail, with a possible cost saving.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3080462 | Casey | Mar 1963 | A |
| 3365561 | Kiesel et al. | Jan 1968 | A |
| 4931603 | Castonguay et al. | Jun 1990 | A |
| 5146194 | Altenhof et al. | Sep 1992 | A |
| 5517164 | Zoller et al. | May 1996 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20070212928 A1 | Sep 2007 | US |
