Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
2003-04-17
2004-11-23
Deb, Anjan (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S509000, C324S424000
Reexamination Certificate
active
06822458
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electrical testing devices. More particularly, the present invention relates to devices for simulating arcing conditions for testing devices such as arc fault circuit interrupters.
BACKGROUND OF THE INVENTION
Arcing in electrical circuits results when electricity discharges from an area of high voltage potential to an area of lower voltage potential across a conductive path. Series type arcing is the low level arcing events that are generally caused by loose or dirty contacts, low contact pressure, or breaks in wire lengths. For example, a break in a wire caused by it being hit by a nail can cause arcing from one side of the broken wire to the other across the air gap. Series type electrical arcing can also result at the point of connection of wires where the connection is corroded or improperly installed.
Some protection against arcing is provided by over current protection devices such as circuit breakers or fuses. As depicted in
FIG. 1
a graph
10
of the trip characteristics of an exemplary circuit breaker or fuse is provided. As depicted, the graph
10
is divided generally into a must hold region
12
, a may trip region
14
, and a must trip region
16
.
In the must hold region
12
the circuit breaker or fuse will not trip even if the current exceeds the rated current of the circuit protection device as long as the duration of such over current is sufficiently short. For example, if the current is seven times the rated current for less than two tenths of a second, the device will not trip.
In the must trip region
16
, the circuit protection device will always trip when the current exceeds the rated current for a sufficiently long duration. For example, when the current exceeds six times the rated current for one second or more the device must trip.
In between the must hold region
12
and must trip region
16
the circuit protection device may or may not trip. It is noted that the performance of such circuit protection devices is temperature dependent and thus the upper and lower boundaries drift upward as the temperature drops, i.e., the same over current condition must exist for a longer period in order for the device to trip. Conversely, the boundaries drift downward as the temperature rises.
Arcing conditions that exist in the must trip region
16
will be protected against by typical circuit breakers and fuses: However, most arcing occurs in the must hold region and thus, these devices do not protect against most arcing conditions.
Protection is also provided, to some extent, by ground fault circuit interrupters which can detect current leakage to ground. Particularly, ground fault circuit interrupters detect differentials in the current flow through the hot and neutral wires. Where a difference exists in current flow through both wires above a set threshold, as would exist where electricity is arcing from the hot wire to a neighboring surface, the circuit is interrupted. Ground fault circuit interrupters are also not particularly effective, however, at detecting series type arcing events where no current path exists to ground.
Arc fault circuit interrupters do provide significant protection against damage caused by series type arcing. These devices utilize discrete electronics to monitor and analyze fluctuations in the current in a circuit and interrupt the circuit if an unwanted arc is detected. Because there is arcing which occurs normally in circuits, such as when a light switch is operated, the algorithms used to analyze the current fluctuations in arc fault circuit interrupters allow these devices to detect and react only to unwanted arcing events. Because of their efficacy, the 2002 National Electrical Code now mandates use of arc fault circuit interrupters for new home construction.
With the development of arc fault circuit interrupters, there is a consequent need for arc fault circuit interrupter test devices. This is particularly true for arc fault circuit interrupters used in applications such as aircraft circuitry. A number of such test devices have therefore been developed which simulate series type arcing.
An example of such a device is the opposed carbon rod series arc detector which is described in the Underwriters Laboratory specification UL 1699. In this type of device, a test starts with two carbon electrodes in physical contact with each other, completing an electrical circuit. The circuit is energized and current is allowed to flow through the carbon electrodes. With one electrode held fixed, the other electrode is slowly drawn away from the first, thus producing a sustainable series arc.
Drawbacks of these types of devices include the exposed arc which contains lethal voltage/current levels, produces ultraviolet light, noxious fumes, and intense light. The high temperatures caused by the arcs are also an ignition source for flammable and explosive materials around the test device.
Another drawback of this type of device is that it produces an arc that does not mimic the randomness associated with series arcing caused by loose or dirty contacts, low pressure, or breaks in wire lengths. Further, the electrodes used in these devices deteriorate with use causing uncontrolled variation of the arcing profile.
Another type of testing device that has been developed utilizes vibrating loose terminals to simulate series type arcs. In this type of device, an electrical terminal strip is attached to a vibration table and wires with crimped rings are loosely attached to the terminal strip by placing the rings around conductive posts protruding from the terminal strip. When the circuit is energized, and the table is vibrating, the loose terminals begin to arc randomly.
Because this type of device generates exposed arcs, it suffers the same drawbacks described above with respect to the exposed arc of the opposed carbon rod series arc generator. In addition, the vibrating loose terminal testing device suffers the problem of precise alignment of the terminals being necessary to initiate arcing.
Vibrating loose terminal test devices are costly to build owing to the use of expensive equipment, a vibration table. These devices are also costly to operate because the oxidation which occurs on the ring terminals and terminal strip requires these components to be replaced at the start of each test.
A third type of existing arc fault circuit interrupter test device generates arcs using electronic components such as silicon controlled rectifiers, field effect transistors, and solid state relays. In these devices, random half cycles of current are switched out to mimic arcing events. The drawbacks of these devices are that no actual arcing occurs and thus the test is not representative of real arcing events.
Accordingly, it is desirable to provide an apparatus and method for simulating series type arcing events that does not generate exposed arcs and thus does not have parts subject to oxidation. It is also desirable that such an apparatus and method generate actual arcs so that real arcing events are simulated.
SUMMARY OF THE INVENTION
The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect an apparatus is provided that in some embodiments simulates an arcing event in a circuit using motion sensitive switches secured in an housing which is moveable in a plane. Movement of the housing causes current disruptions within the switches which mimic arcing events.
In accordance with one aspect of the present invention, an arc simulating apparatus is provided having a housing. A number of motion sensitive switches are connected in series and secured within the housing. A first terminal wire is connected to a first pole of the series circuit of switches and a second terminal wire is connected to a second pole of the series circuit of switches.
In accordance with another aspect of the invention, a method of simulating an arc in a circuit is provided wherein a housing containing a series connection of a number of motion sensitive switches is moved in order to interrupt a c
Baker & Hostetler LLP
Benson Walter
Deb Anjan
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