Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
1998-02-19
2001-06-12
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
Reexamination Certificate
active
06246556
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the protection of electrical circuits and, more particularly, to the detection of various electrical faults in an electrical circuit, for example an analysis of current flow in the circuit, detection of arcing faults and detection of ground faults.
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. Interruption of the circuit reduces the risk of injury or the potential of property damage from a resulting fire.
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 reach an unacceptable temperature. Arcing faults can cause fire if combustible materials are in close proximity.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electrical fault detection system and method which reliably detects electrical faults, including overcurrent conditions and ground faults, as well as arc fault conditions ignored by conventional circuit interrupters.
Still another object of the invention is to provide an electrical fault detection system which utilizes a minimum number of highly reliable electronic components 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 an electrical circuit fault detector comprising band-pass filter circuit means responsive to an input signal representative of an electrical signal condition in a circuit to be monitored for passing a frequency signal comprising signal components of said input signal which fall within a first predetermined frequency band; threshold detector circuit means coupled to said band-pass filters circuit means and responsive to components of said frequency signal above a predetermined threshold amplitude for producing a corresponding frequency amplitude signal; and first frequency signal conditioning circuit means coupled to said threshold detector means and responsive to said frequency amplitude signal for producing a conditioned frequency amplitude output signal in a form suitable for input to a controller.
In accordance with another aspect of the invention, there is provided an electrical fault detector system comprising a first sensor operatively coupled with a circuit to be monitored for producing an input signal representative of a signal condition in said circuit to be monitored; a ground fault sensor operatively coupled with said circuit to be monitored for producing a ground fault input signal representative of a ground fault current in said circuit to be monitored; integrator circuit means coupled with said first sensor and responsive to said input signal for developing a current signal representative of current magnitude in said circuit to be monitored; band-pass filter circuit means operatively coupled with said first sensor and responsive to said input signal for passing a frequency signal comprising signal components of said input signal in a predetermined frequency band; ground fault amplifier circuit means coupled with said ground fault sensor for amplifying said input signals to produce amplified ground fault signals; and signal conditioning circuit means coupled with said band-pass filter circuit means, said integrator circuit means and said ground fault amplifier circuit means for receiving and conditioning said current signal, said frequency signal and said amplified ground fault signal to produce conditioned output signals in a form suitable for input to a controller.
In accordance with another aspect of the invention, there is provided a method of detecting arcing faults in an electrical distribution system that includes a line conductor connected to a load, said method comprising monitoring the line conductor and producing a corresponding input signal; and band-pass filtering said input signal at two predetermined frequency bands.
In accordance with another aspect of the invention, there is provided an application specific integrated circuit comprising band-pass filter circuit means responsive to an input signal representative of a signal condition in a circuit to be monitored for passing a frequency signal comprising signal components of said input signal which fall within a first predetermined frequency band; threshold detector circuit means coupled to said band-pass filters circuit means and responsive to components of said frequency signal above a predetermined threshold amplitude for producing a corresponding frequency amplitude signal; and first frequency signal conditioning circuit means coupled to said threshold detector circuit means and responsive to said frequency amplitude signal for producing a conditioned frequency amplitude output signal in a form suitable for input to a controller.
In accordance with another aspect of the invention, there is provided an electrical fault detector circuit comprising current fault detector circuit means for developing a current signal representative of current magnitude in said circuit to be monitored; arcing fault detector circuit means for developing an arcing fault signal in response to detection of an arcing fault in said circuit to be monitored; and ground fault detector circuit means for producing a ground fault signal in response to detection of a ground fault in the circuit to be monitored.
In accordance with another aspect of the invention, there is provided an application specific integrated circuit for an electrical fault detector system comprising current fault detector circuit means for developing a current signal representative of current magnitude in said circuit to be monitored; arcing fault detector circuit means for developing an arcing fault signal in response to detection of an arcing fault signal in said circuit to be monitored; and ground fault detector circuit means for producing a ground fault signal in response to detection of a ground fault in the circuit to be monitored.
In accordance with another aspect of the invention, there is provided a
Coats Alan G.
Dvorak Robert F.
Haun Andrew A.
Scott Gary W.
Wong Kon B.
Golden Larry I.
Irfan Kareem M.
Leja Ronald W.
Square D Company
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