Faulted circuit detector having isolated indicator
First Claim
1. An apparatus for detecting the presence of faults on an electrical conductor;
- comprising;
mean for sensing an overcurrent condition in the electrical conductor, said sensing means comprising a temperature compensation circuit for negating the effect of temperature change on said sensing means;
means remote from said sensing means for indicating the presence of an overcurrent condition in the electrical conductor;
means for communicating the presence of an overcurrent condition sensed by said sensing means to said indicating means;
means for automatically resetting said indicating means;
means for disabling the automatic operation of said resetting means when a predetermined minimum voltage is not present on the electrical conductor; and
said temperature compensation circuit comprisinga current transformer having a wire coil, said wire coil having a positive temperature coefficient;
a thermistor having a negative temperature coefficient; and
a resistor connected in parallel with said thermistor, said resistor having a negligible resistance change at temperatures within the range of approximately -40 degrees C. to +85 degrees C.
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Accused Products
Abstract
A faulted circuit detector having an electrically isolated and remotely positioned indicator detects fault currents in a monitored conductor. When a fault of a predetermined magnitude is detected, a light pulse is transmitted from the detector to the indicator via a fiber optic cable where, upon receipt, the pulse is converted to an electrical pulse causing the indicator to indicate a "fault" state. A reset circuit within the indicator resets the indicator at regular intervals to the "normal" state as long as a predetermined minimum voltage is present on the monitored conductor. The detector includes a temperature compensation circuit and low pass filter circuit so as to prevent misoperation due to varying ambient temperatures or high frequency transients. A test circuit is also provided to allow service personnel to field-test the device with the monitored conductor in an energized state.
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Citations
14 Claims
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1. An apparatus for detecting the presence of faults on an electrical conductor;
- comprising;
mean for sensing an overcurrent condition in the electrical conductor, said sensing means comprising a temperature compensation circuit for negating the effect of temperature change on said sensing means; means remote from said sensing means for indicating the presence of an overcurrent condition in the electrical conductor; means for communicating the presence of an overcurrent condition sensed by said sensing means to said indicating means; means for automatically resetting said indicating means; means for disabling the automatic operation of said resetting means when a predetermined minimum voltage is not present on the electrical conductor; and said temperature compensation circuit comprising a current transformer having a wire coil, said wire coil having a positive temperature coefficient; a thermistor having a negative temperature coefficient; and a resistor connected in parallel with said thermistor, said resistor having a negligible resistance change at temperatures within the range of approximately -40 degrees C. to +85 degrees C. - View Dependent Claims (2)
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3. Apparatus for detecting a fault on a monitored electrical conductor, comprising:
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means for sensing a fault in the conductor, said sensing means including a temperature compensation circuit for negating the effect on said sensing means of temperature changes within the range of approximately -40 degrees C. to +85 degree C., and including a low pass filter circuit for filtering out undesirable high frequency transients induced in said sensing means; means for remote from said sensing means for indicating the presence of a fault in the electrical conductor; means for communicating the presence of a fault sensed by said sensing means to said indicating means; means for automatically resetting said indicating means; and means for disabling automatic operation of said resetting means unless a predetermined minimum voltage is present on the conductor; said communication means electrically isolating said sensing means from said indicating means; said resetting means continually resetting said indicating means at regular predetermined intervals unless disabled by said disabling means; said disabling means comprising a hold-off circuit for deactivating said resetting means when said predetermined voltage is not present on the conductor; and said temperature compensation circuit comprising; a current transformer having a wire coil, said wire coil having a positive temperature coefficient; a thermistor having a negative temperature coefficient; and a resistor connected in parallel with said thermistor, said resistor having a negligible resistance change at temperatures within the range of approximately -40 degrees C. to +85 degrees C.
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4. Apparatus for indicating that a fault of a predetermined current magnitude has occurred in a monitored electrical conductor on the high voltage side of an electrical distribution transformer, comprising:
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a sensor for generating a signal proportional to the current in the monitored conductor; a low pass filter for filtering high frequency transients in the signal generated by said sensor to prevent the transients from causing misoperation of the apparatus; an optic transmitter for transmitting a light pulse when a fault condition has been sensed by said sensor; an optic receiver for receiving said light pulse and transforming said pulse into an electrical pulse; an indicator for indicating the presence of a fault condition in the monitored conductor upon receipt of said electrical pulse, said indicator having first and second indication states for, respectively, displaying indications of "normal" or "fault" conditions; a reset circuit for resetting said indicator from the second of said indication states to the first of said indication states; and a hold-off circuit for delaying the reset circuit from resetting said indicator unless a predetermined minimum voltage is present on the low voltage side of the electrical distribution transformer. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An apparatus for detecting the presence of faults on an electrical conductor, comprising:
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a sensor for sensing an overcurrent condition in the electrical conductor, said sensor comprising a temperature compensation circuit for negating the effect of temperature change on said sensing means, said temperature compensation circuit comprising; a current transformer having a wire coil, said wire coil having a positive temperature coefficient; a thermistor having a negative temperature coefficient; and a resistor connected in parallel with said thermistor, said resistor having a negligible resistance change at temperatures within the range of approximately -40 degrees C. to +85 degrees C.; an indicator for indicating the presence of an overcurrent condition in the electrical conductor; and a signal transmitter for communicating the presence of an overcurrent condition sensed by said sensor to said indicator.
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Specification