Patent Application
20070132531
1. Field of the Invention
This invention pertains generally to circuit interrupters and, more particularly, to two pole circuit interrupters, such as two pole arc fault or ground fault circuit breakers.
2. Background Information
Circuit interrupters include, for example, circuit breakers, contactors, motor starters, motor controllers, other load controllers and receptacles having a trip mechanism. Circuit breakers are generally old and well-known in the art. Examples of circuit breakers are disclosed in U.S. Pat. Nos. 5,260,676; and 5,293,522.
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which is heated and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature, which is attracted by the sizable magnetic forces generated by a short circuit or fault, also unlatches, or trips, the operating mechanism.
In many applications, the miniature circuit breaker also provides ground fault protection. Typically, an electronic circuit detects leakage of current to ground and generates a ground fault trip signal. This trip signal energizes a shunt trip solenoid, which unlatches the operating mechanism, typically through actuation of the thermal-magnetic trip device. See, for example, U.S. Pat. Nos. 5,260,676; and 5,293,522.
Recently, there has been considerable interest in also providing protection against arc faults. Arc faults are intermittent high impedance faults which can be caused, for instance, by worn insulation between adjacent conductors, by exposed ends between broken conductors, by faulty connections, and in other situations where conducting elements are in close proximity. Because of their intermittent and high impedance nature, arc faults do not generate currents of either sufficient instantaneous magnitude or sufficient average RMS current to trip the conventional circuit interrupter. Even so, the arcs can cause damage or start a fire if they occur near combustible material. It is not practical to simply lower the pick-up currents on conventional circuit breakers, as there are many typical loads, which draw similar currents and would, therefore, cause nuisance trips. Consequently, separate electrical circuits have been developed for responding to arc faults. See, for example, U.S. Pat. Nos. 5,224,006; and 5,691,869.
There is a need for a duplex (twin) arc fault circuit interrupter (AFCI), such as a duplex (twin) arc fault circuit breaker. Due to the relatively small size of many single-pole circuit breakers, the use of two AFCI trip circuits is prohibitive based upon both power dissipation and packaging constraints.
Accordingly, there is room for improvement in arc fault circuit interrupters.
These needs and others are met by the present invention, which employs a single arc fault circuit interrupter (AFCI) or ground fault circuit interrupter (GFCI) trip circuit in combination with two poles of a duplex or twin AFCI or GFCI. Each one of the two poles of the duplex or twin AFCI or GFCI shares a common line conductor and a common neutral conductor. The single AFCI or GFCI trip circuit is employed in order to permit both poles to trip together whenever an arc fault or ground fault is electronically detected.
In accordance with one aspect of the invention, an arc fault circuit interrupter comprises: a housing; two poles in the housing, each of the poles comprising: separable contacts, an operating mechanism structured to open and close the separable contacts, and a trip mechanism cooperating with the operating mechanism to trip open the separable contacts; and a single arc fault trip circuit cooperating with the operating mechanisms of the two poles to trip open the separable contacts of the two poles whenever an arc fault is detected by the single arc fault trip circuit.
The single arc fault trip circuit may comprise a trip solenoid cooperating with the operating mechanisms of the two poles to contemporaneously trip open the separable contacts of the two poles.
As another aspect of the invention, an arc fault circuit interrupter comprises: a housing; two poles in the housing, each of the poles comprising: separable contacts comprising a line side and a load side, an operating mechanism structured to open and close the separable contacts, and a trip mechanism cooperating with the operating mechanism to trip open the separable contacts; a line conductor including a line current, the line conductor being electrically interconnected with the line side of the separable contacts of the two poles; a neutral conductor; a first load conductor electrically interconnected with the load side of the separable contacts of one of the two poles; a second load conductor electrically interconnected with the load side of the separable contacts of the other one of the two poles; a first load neutral conductor electrically interconnected with the neutral conductor, the first load neutral conductor including a first neutral current; a second load neutral conductor electrically interconnected with the neutral conductor, the second load neutral conductor including a second neutral current; a single arc fault trip circuit cooperating with the operating mechanisms of the two poles to trip open the separable contacts of the two poles, the single arc fault trip circuit comprising: (a) a shunt electrically connected in series with the line conductor and structured to sense the line current thereof, or (b) a first shunt electrically connected in series with the first load neutral conductor and structured to sense the first neutral current and a second shunt electrically connected in series with the second load neutral conductor and structured to sense the second neutral current, wherein the two poles trip together whenever an arc fault is detected by the single arc fault trip circuit.
The single arc fault trip circuit may comprise the shunt electrically connected in series with the line conductor, the shunt electrically connected in series with the line conductor may include a current signal, and the single arc fault trip circuit may further comprise an arc fault trip mechanism and a series RC circuit coupling the current signal to the arc fault trip mechanism.
The neutral conductor may be electrically interconnected with the single arc fault trip circuit, and the single arc fault trip circuit may further comprise a trip solenoid cooperating with the operating mechanisms of the two poles to trip open the separable contacts of the two poles and a contact controlled by the trip solenoid, the contact being structured to disconnect the neutral conductor from the single arc fault trip circuit.
The single arc fault trip circuit may comprise the first shunt and the second shunt. The first shunt may include a first current signal, the second shunt may include a second current signal, and the single arc fault trip circuit may further comprise an arc fault trip mechanism, a first series RC circuit coupling the first current signal to the arc fault trip mechanism and a second series RC circuit coupling the second current signal to the arc fault trip mechanism.
The line conductor may be electrically interconnected with the single arc fault trip circuit, and the single arc fault trip circuit may further comprise a trip solenoid cooperating with the operating mechanisms of the two poles to trip open the separable contacts of the two poles and a contact controlled by the trip solenoid, the contact being structured to disconnect the line conductor from the single arc fault trip circuit.
The single arc fault trip circuit may be structured to provide backfeed protection.
The line conductor may be electrically interconnected with the single arc fault trip circuit, and the single arc fault trip circuit may further comprise a contact structured to disconnect the line conductor from the single arc fault trip circuit when the single arc fault trip circuit trips open the two poles.
The single arc fault trip circuit may further comprise a trip solenoid cooperating with the operating mechanisms of the two poles to contemporaneously trip open the separable contacts of the two poles.
The trip solenoid may comprise a first flag structured to trip open one of the two poles and a second trip flag structured to trip open the other one of the two poles. The first flag may pull or push the one of the two poles to trip the one of the two poles, and the second trip flag may pull or push the other of the two poles to trip the other of the two poles.
The single arc fault trip circuit may be normally powered from the line conductor and the neutral conductor, and the single arc fault trip circuit may be unpowered after the single arc fault trip circuit cooperates with the operating mechanisms of the two poles to trip open the separable contacts of the two poles.
The single arc fault trip circuit may be powered from the line conductor and the neutral conductor when at least one of the two poles is not tripped.
As another aspect of the invention, a ground fault circuit interrupter comprises: a housing; two poles in the housing, each of the poles comprising: separable contacts, an operating mechanism structured to open and close the separable contacts, and a trip mechanism cooperating with the operating mechanism to trip open the separable contacts; and a single ground fault trip circuit cooperating with the operating mechanisms of the two poles to trip open the separable contacts of the two poles whenever a ground fault is detected by the single ground fault trip circuit.
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 statement that a part is “electrically interconnected with” one or more other parts shall mean that the parts are directly electrically connected together or are electrically connected together through one or more electrical conductors or generally electrically conductive intermediate parts. Further, as employed herein, the statement that a part is “electrically connected to” one or more other parts shall mean that the parts are directly electrically connected together or are electrically connected together through one or more electrical conductors.
The present invention is described in association with arc fault circuit breakers, although the invention is applicable to a wide range of circuit interrupters for arc fault and/or ground fault applications.
The single arc fault trip circuit 8 may include a trip solenoid 9 cooperating with the operating mechanisms 6 of the two poles 3,4 to contemporaneously trip open the separable contacts 5 of such poles.
The example trip mechanisms of the two poles 3,4 are thermal/magnetic trip mechanisms 7, although any suitable (non-arc fault) trip mechanism may be employed.
Referring to
Preferably, the single arc fault trip circuit 44 is structured to provide backfeed protection as will be discussed in greater detail, below, in connection with
The single arc fault trip circuits 44,54 of
The trip mechanisms 26,27 (e.g., as shown in
The single arc fault trip circuits 44,54 may further include a ground fault trip circuit as will be discussed, below, in connection with
The two poles 14,16 of
Although not shown, the arc fault circuit breaker 60 of
The line conductor 28 is electrically interconnected with the single arc fault trip circuit 44 through the contact 50. The trip solenoid 74 cooperates with the operating mechanisms 24,25 of the two poles 14,16 (
In this example, the arc fault trip circuit 44 includes both the AFD 82 and a ground fault detector (GFD) 92. The AFD 82 may be, for instance, of the type which detects the step increases in current which occur each time an arc is struck, although other types of arc fault detectors could also be used. Suitable arc fault detectors are disclosed, for instance, in U.S. Pat. No. 5,224,006, with a preferred type described in U.S. Pat. No. 5,691,869, which is incorporated by reference herein. In accordance with an important aspect of the invention, the AFD 82 senses the load neutral currents 40,42 (
When the time attenuated accumulation of the pulses reaches a selected level, the AFD 82 generates at its output an arc fault trip signal 96, which is active in response to arc fault(s) associated with one (or both) of the load neutral currents 40,42 (
The GFD 92 may be of the well-known dormant oscillator type in which case it utilizes at least one sensing coil, such as 98, to detect both line-to-ground and neutral-to-ground fault current conditions. If the AFD 82 detects an arc fault, the trip signal 96 is generated, which turns on a switch, such as the silicon controlled rectifier (SCR) 100, to energize the trip solenoid 74. When the GFD 92 detects a ground fault, it generates at its output a ground fault trip signal 102, which is active in response to the ground fault. The ground fault trip signal 102 is “ORed” with the arc fault trip signal 96 (i.e., an “OR” function of the outputs of the GFD 92 and the AFD 82), such that the combination of the signals 96,102 turns the SCR 100 on, energizes the trip solenoid 74 and, thereby, actuates the operating mechanisms 24,25 to open the separable contacts 18,19 in response to the arc fault or ground fault. A capacitor 104 protects the gate of the SCR 100 from voltage spikes and false tripping due to noise. An MOV or transorb 106 protects the trip solenoid 74 and SCR 100 from overvoltage conditions.
Both the AFD 82 and the GFD 92 may have test circuits (not shown). Examples of such test circuits are disclosed in U.S. Pat. Nos. 5,982,593; and 6,707,651, which are incorporated by reference herein.
The neutral conductor 30 is electrically interconnected with the single arc fault trip circuit 44 through the contact 52. The trip solenoid 74 cooperates with the operating mechanisms 24,25 of the two poles 14,16 (
The single trip circuits 44,54 may be employed by two-pole circuit interrupters for ground fault applications.
Although an analog AFD 82 is disclosed, it will be appreciated that a combination of one or more of analog, digital and/or processor-based circuits may be employed.
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.
