Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
1998-08-05
2001-07-10
Wachsman, Hal (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S064000, C702S066000, C702S069000, C361S063000, C361S087000, C700S292000, C700S293000
Reexamination Certificate
active
06259996
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the protection of electrical circuits and, more particularly, to the detection of electrical faults of the type known as arcing faults in an electrical circuit.
BACKGROUND OF THE INVENTION
The electrical systems in residential, commercial and industrial applications usually include a panelboard for receiving electrical power from a utility source. The power is then routed through protection devices to designated branch circuits supplying one or more loads. These overcurrent devices are typically circuit interrupters such as circuit breakers and fuses which are designed to interrupt the electrical current if the limits of the conductors supplying the loads are surpassed.
Circuit breakers are a preferred type of circuit interrupter because a resetting mechanism allows their reuse. Typically, circuit breakers interrupt an electric circuit due to a disconnect or trip condition such as a current overload or ground fault. The current overload condition results when a current exceeds the continuous rating of the breaker for a time interval determined by the trip current. A ground fault trip condition is created by an imbalance of currents flowing between a line conductor and a neutral conductor which could be caused by a leakage current or an arcing fault to ground.
Arcing faults are commonly defined as current through ionized gas between two ends of a broken conductor or at a faulty contact or connector, between two conductors supplying a load, or between a conductor and ground. However, arcing faults may not cause a conventional circuit breaker to trip. Arcing fault current levels may be reduced by branch or load impedance to a level below the trip curve settings of the circuit breaker. In addition, an arcing fault which does not contact a grounded conductor or person will not trip a ground fault protector.
There are many conditions that may cause an arcing fault. For example, corroded, worn or aged wiring, connectors, contacts or insulation, loose connections, wiring damaged by nails or staples through the insulation, and electrical stress caused by repeated overloading, lightning strikes, etc. These faults may damage the conductor insulation and cause the conductor to reach an unacceptable temperature.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an arc fault detection system and method which reliably detects arc fault conditions which may be ignored by conventional circuit interrupters.
Another object of the invention is to provide an arc fault detection system which utilizes a minimum number of highly reliable electronic signal processing components, such as a microcontroller, to perform most of the signal processing and analyzing functions, so as to be relatively simple and yet highly reliable in operation.
Other and further objects and advantages of the invention will be apparent to those skilled in the art from the present specification taken with the accompanying drawings and appended claims.
In accordance with one aspect of the invention, there is provided a method of determining whether arcing is present in an electrical circuit comprising the steps of sensing a change in current in said circuit and developing a corresponding input signal, analyzing said input signal to determine the presence of broadband noise in a predetermined range of frequencies, and producing a corresponding output signal, and processing said current signal and said output signal in a predetermined fashion to determine whether an arcing fault is present in said circuit.
In accordance with another aspect of the invention, there is provided a system for determining whether arcing is present in an electrical circuit comprising a sensor for sensing a changing current in said circuit and developing a corresponding sensor signal, a circuit for analyzing said sensor signal to determine the presence of broadband noise in a predetermined range of frequencies, and producing a corresponding output signal, and a controller for processing said sensor signal and said output signal in a predetermined fashion to determine whether an arcing fault is present in said circuit.
In accordance with another aspect of the invention, there is provided a controller for determining whether arcing is present in an electrical circuit in response to input signals, said input signals corresponding to a changing current in said circuit and to the presence of broadband noise in a predetermined range of frequencies in said circuit, said controller including a plurality of counters and wherein said controller increments said plurality of counters in a predetermined fashion in accordance with said input signals and periodically determines whether an arcing fault is present based at least in part on the state of said plurality of counters.
In accordance with another aspect of the invention, there is provided a method of determining whether arcing is present in an electrical circuit by processing input signals corresponding to a changing current in said circuit and to the presence of broadband noise in a predetermined range of frequencies in said circuit, said method comprising the steps of incrementing a plurality of counters in a predetermined fashion in accordance with said input signals, and periodically determining whether an arcing fault is present based at least in part on the state of said plurality of counters.
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patent:
Coats Alan G.
Dvorak Robert F.
Haun Andy A.
Scott Gary W.
Wong Kon B.
Golden Larry I.
Square D Company
Trfan Kareem M.
Wachsman Hal
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