Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Automatic circuit-interrupting devices
Reexamination Certificate
2000-02-15
2001-10-23
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Automatic circuit-interrupting devices
C335S018000, C335S021000, C335S038000, C335S041000, C335S172000, C335S174000
Reexamination Certificate
active
06307453
ABSTRACT:
RELATED APPLICATION
Commonly owned, concurrently filed application entitled “Circuit Breaker with Latch and Toggle Mechanism Operating in Perpendicular Planes” and identified by 09/504,421 U.S. Pat. No. 6,225,883.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to circuit breakers of the type having a trip motor energized by a trip circuit responsive to selected fault conditions producing overcurrents smaller in magnitude than short circuit currents. In particular, it relates to a circuit breaker that couples the magnetic flux generated by short circuit currents into the magnetic circuit of the trip motor to trip the circuit breaker open independently of energization of the trip motor coil by the trip circuit. Such an arrangement is particularly advantageous in providing an instantaneous trip function for subminiature circuit breakers, but can also be applied to larger circuit breakers.
2. Background Information
One use of subminiature circuit breakers is in aircraft electrical systems where they not only provide overcurrent protection but also serve as switches for turning equipment on and off. As such, they are subjected to heavy use and therefore must be capable of performing reliably over many operating cycles. They also must be small to accommodate the high density layout of circuit breaker panels which make circuit breakers for numerous circuits accessible to a user. Subminiature circuit breakers can be used in an environment where they are subject to vibration. The circuit breaker must trip consistently within tolerance yet not be tripped out by vibration or shock loading.
Typically, subminiature circuit breakers have only provided protection against persistent overcurrents implemented by a latch triggered by a bimetal responsive to I
2
R heating resulting from the overcurrent. Some aircraft systems have also provided ground fault protection, but through the use of additional devices, namely current transformers which in some cases are remotely located from the protective relay. There is a growing interest in providing additional protection, and most importantly arc fault protection. Currently available subminiature circuit breakers do not respond to arc faults which are typically high impedance faults and can be intermittent. Nevertheless, such arc faults can result in a fire. Finally, there is an interest in providing an instantaneous trip in response to very high overcurrents such as would be drawn by a short circuit.
While larger circuit breakers, even the “miniature” circuit breakers used in residential applications provide multiple protection functions, the currently available subminiature circuit breakers do not have such combined features. Again, the challenge is to provide alternative protection in a very small package which will operate reliably with heavy use over a prolonged period. A device which meets all the above criteria and can be automatically assembled is desirable.
SUMMARY OF THE INVENTION
The present invention is directed to a circuit breaker which can be miniaturized yet provides multiple protection functions. The circuit breaker has a main current conductor connected in series with the separable contacts and routed to induce magnetic flux in a trip motor which can be separately energized by an electronic trip circuit to actuate the latch member of a latchable operating mechanism to trip the separable contacts of the circuit breaker open. An overcurrent through the main current conductor of at least a predetermined magnitude, such as would be associated with a short circuit, actuates the latch member independently of energization of the trip motor coil to provide an instantaneous trip function for the circuit breaker.
More particularly, the circuit breaker comprises a housing, separable contacts mounted in the housing, a latchable operating mechanism including a latch member which when actuated unlatches to open the separable contacts, and a trip motor which actuates the latch member when energized. The circuit breaker further has an overcurrent assembly which includes a main current conductor connected in series with the separable contacts and routed to induce magnetic flux in the magnetic circuit of the trip motor to actuate the latch member in response to an overcurrent through the main current conductor of at least a predetermined magnitude. Finally, the circuit breaker includes a trip circuit energizing the trip motor in response to predetermined current conditions below the overcurrent of predetermined magnitude. Preferably, these predetermined current conditions can be for instance an arc fault.
The trip motor includes a coil and a magnetic circuit with the main current conductor being routed at least partially through this magnetic circuit so that magnetic flux generated by current in the main current conductor is coupled into the magnetic circuit thereby actuating the latch member. Preferably the main conductor is a flexible conductor and the trip motor further includes a bracket which extends the magnetic circuit of the trip motor at least partially around the flexible conductor. In the exemplary embodiment of the invention a frame which supports the latchable operating mechanism cooperates with the bracket to guide the flexible conductor through the magnetic circuit of the trip motor. The bracket is magnetically permeable to enhance the magnetic coupling of the flux generated in the flexible shunt into the magnetic circuit of the trip motor. Preferably, the latch member of the latchable operating mechanism forms the armature of the trip motor which is attracted by flux generated in the magnetic circuit either by energization of the trip coil or a current of at least the predetermined magnitude in the main current conductor.
REFERENCES:
patent: 4812799 (1989-03-01), Cobb, III et al.
patent: 5224006 (1993-06-01), MacKenzie et al.
patent: 5757602 (1998-05-01), Meili et al.
patent: 5886860 (1999-03-01), Chen et al.
Juds Mark Allan
Moldovan Peter Klaus
Rollmann Paul Jason
Wellner Edward Louis
Barrera Ramon M.
Eaton Corporation
Union Marvin L.
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