Arc fault detector with diagnostic indicator

Details Arc fault detector with diagnostic indicator Arc fault detector with diagnostic indicator

2001-12-11

2003-11-25

Tso, Edward H. (Department: 2838)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific quantity comparison means

C324S500000

Reexamination Certificate

active

06654219

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to the field of arc fault detectors, and more particularly to an arc fault detector that indicates what type of arc fault is detected.
BACKGROUND OF THE INVENTION
The Underwriters Laboratories requirements for the family of arc fault circuit interrupters, as defined in their standard 1699, require the device to sense a variety of arcing conditions within a branch circuit of an AC electrical power distribution system and in appliance conductors receiving power therefrom, to be referred to as an electrical circuit, and to interrupt the flow of electrical current before an arcing condition causes flammable ignition of nearby combustibles. The ability to locate the arcing condition in the electrical circuit to mediate repair is often difficult since the arcing condition could be occurring in a portion of the electrical circuit that is hidden behind sheet rock or that is in a remote space. Even if the arcing condition is occurring in a visible portion of the electrical circuit, visibility of the arc could be denied by the arc fault circuit interrupter itself because of interrupting the arc before the arc becomes visible.
Arc faults known as “A-type” are those in which the arcing condition occurs across a discontinuity in the line or neutral conductor of the electrical circuit. Such discontinuities include a broken conductor, a frayed cord set, a loose terminal, or a poor connection within a wire nut. An A-type arc fault occurs when load current conducts intermittently through the discontinuity, commonly known as “sputtering current.” Since the current through the A-type fault is limited by the impedance of the load itself, because the fault is in series with the load, an A-type fault is also known as a “series fault.”
Arc faults known as “B-type” are a second type of arc fault condition. In a B-type arc fault, the arc occurs across two conductors in the branch circuit or any extension cords plugged into it, at a site where the insulating media separating the two conductors has been compromised. The arc may occur across the line and neutral conductors or the line and ground conductors, or in the case of reverse polarity where the line and neutral conductors are connected to the supply voltage in reverse, the arc may occur across the neutral and ground conductors. The current through the B-type fault is not limited by the impedance of the load, but instead by the available current from the supply voltage as limited by the loop impedance of the conductors and terminals between the source of supply voltage and the position of the parallel fault, i.e., specifically by the impedance of the conductive members carrying the fault current. Since B-type faults are effectively across the line, they have been known as “parallel faults.”
The arc fault circuit interrupter may be incorporated in various housings associated with electrical circuits including receptacles, circuit breakers, boxes devoid of receptacles, or plugs. Each device has a line side, also known as the upstream side, from which electrical power is received from the electrical power distribution system, and a load side, also known as the downstream side, from which electrical power is conveyed to a load.
Various circuit interrupters protect wiring circuits at different locations. Underwriters Laboratories requires downstream parallel arc faults to be interrupted by these devices: branch feeder arc fault circuit interrupter, combination arc fault circuit interrupter, outlet branch circuit arc fault interrupter, and outlet plug arc fault circuit interrupter. Loop currents in upstream parallel arc faults are not interruptible by the arc fault circuit interrupter because interrupting the circuit downstream of a parallel arc fault has no effect on the fault.
The arc fault devices must detect parallel arc faults in which the available current to the parallel fault is as high as 500 amperes, above which the overcurrent device (fuse or circuit breaker) has been determined to afford protection. Since the parallel arc fault current is established by the value of the loop impedance, the lowest value of parallel arc fault current is typically considered to be 75 amperes.
The combination arc fault circuit interrupter, the outlet branch circuit interrupter, and outlet arc fault circuit interrupter are required by UL to detect series faults in which the load is as low as 5 amperes, which was determined by UL to be the lowest current at which the risk of ignition of nearby combustibles is likely to occur. The highest series arc fault current slightly exceeds the rating of the upstream overcurrent device required by code to protect the branch circuit, for example, 30 amperes. For each of these types of arc fault circuit interrupters, the discontinuity, or series fault, can be upstream or downstream of the device.
Considering both series and parallel arc faults, the AFCI's must be able to cover a range of fault currents from 5 amperes to 500 amperes. The test methodologies in the UL standard for generating series and parallel arc faults differ in order to establish the two different types of faults. The standard allows for a longer interrupting time of the AFCI for lower energy series arcs than for higher energy parallel arcs, without sacrificing the protective benefit or risking ignition of nearby combustibles, further emphasizing that there are different types of arc faults.
Arc faults have been detected on the basis of monitoring the current or voltage of the electrical circuit to be protected. It is important to distinguish signals from arcing conditions that would result in the ignition of combustibles from arc-mimicking signals caused in normal everyday use, such as arcs produced by motor brushes or the toggling of wall switches, or by environmental factors such as lightning. The arc fault circuit interrupter may inadvertently trip in response to high energy arc-mimicking signals, occurring either upstream or downstream of the arc fault circuit interrupter, that present a signal to the arc fault detector that is normally unique to true A-type or B-type arcing conditions.
Many methods are well known in the prior art for identifying the type of arc, de-sensitizing detection of arc-mimicking noise, and determining whether the arcing condition or arc-mimicking condition is upstream or downstream, such as, for example, are disclosed in U.S. patent application Ser. No. 09/828,622 filed Apr. 6, 2001 and entitled AFCI DEVICE WHICH DETECTS UPSTREAM AND DOWNSTREAM SERIES AND PARALLEL ARC FAULTS; U.S. patent application Ser. No. 09/788,206 filed Feb. 16, 2001 and entitled ARC FAULT CIRCUIT INTERRUPTER RECOGNIZING ARC NOISE BURST PATTERNS; U.S. patent application Ser. No. 09/776,582 filed Feb. 2, 2001 and entitled AFCI WHICH DETECTS AND INTERRUPTS LINE SIDE ARCING; U.S. patent application Ser. No. 09/990,809 filed Nov. 16, 2001 and entitled ARC FAULT CIRCUIT DETECTOR HAVING TWO ARC FAULT DETECTION LEVELS; and U.S. patent application Ser. No. 09/992,055 filed Nov. 14, 2001 and entitled UPSTREAM/DOWNSTREAM ARC FAULT DISCRIMINATOR, each of which is incorporated herein by reference.
SUMMARY OF THE INVENTION
Briefly stated, a protection device for an electrical circuit having a load includes a sensor operatively associated with the electrical circuit to sense current changes and voltage fluctuations in the electrical circuit. A detector receives input from the sensor and compares the input to known arc fault signatures and arc fault mimicking signatures to determine what category of arc fault or mimicked arc fault occurs. The detector then produces an encoded output signal indicative of the category of arc fault or mimicked arc fault. Categories of arc faults include upstream or downstream series, downstream parallel, downstream line to line, and downstream line to ground.
According to an embodiment of the invention, a device for detecting an electrical fault in a power line having electrical faults includes detection means for detecting a category and location of an occurring fault; and output m

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