Ground fault circuit interrupting device with grounded neutral detection
First Claim
1. A module for utilization in a ground fault circuit interrupting device wired into a power distribution circuit comprising at least one line conductor and a neutral conductor, said module comprising, in combination:
- A. a differential current transformer including1. a core in which is developed a magnetic flux occasioned by a current imbalance in the line and neutral conductors of the distribution circuit, and a secondary winding wound on said core;
B. an output element connected across said secondary winding for developing a signal voltage indicative of the magnitude of secondary current developed as a result of the current imbalance;
C. a normally conductive electronic switch connected across said secondary winding in shunt with said output element; and
D. a neutral transformer having a secondary winding for connection in series with the neutral conductor and a primary winding; and
E. a pulse generator connected to supply a periodic pulse output through said primary winding of said neutral transformer to render said switch non-conductive for the interval of said pulse and thereby divert said secondary current through said output element pursuant to developing said signal voltage.
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Accused Products
Abstract
The secondary winding of the differential current transformer in a ground fault circuit interrupter is normally short circuited through an electronic switch. A relaxation oscillator, including a timing capacitor, acts to periodically open the switch and divert any secondary current through a burden resistor, developing thereacross a relatively high amplitude fault signal voltage indicative of a liine ground fault. The timing capacitor discharges through the primary winding of a second transformer coupled with the neutral conductor to develop, in the event of a desensitizing neutral ground fault, a fault signal voltage across the burden resistor.
46 Citations
8 Claims
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1. A module for utilization in a ground fault circuit interrupting device wired into a power distribution circuit comprising at least one line conductor and a neutral conductor, said module comprising, in combination:
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A. a differential current transformer including 1. a core in which is developed a magnetic flux occasioned by a current imbalance in the line and neutral conductors of the distribution circuit, and a secondary winding wound on said core; B. an output element connected across said secondary winding for developing a signal voltage indicative of the magnitude of secondary current developed as a result of the current imbalance; C. a normally conductive electronic switch connected across said secondary winding in shunt with said output element; and D. a neutral transformer having a secondary winding for connection in series with the neutral conductor and a primary winding; and E. a pulse generator connected to supply a periodic pulse output through said primary winding of said neutral transformer to render said switch non-conductive for the interval of said pulse and thereby divert said secondary current through said output element pursuant to developing said signal voltage. - View Dependent Claims (2, 3)
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4. A ground fault circuit interrupting device for interrupting an electrical power distribution circuit including at least one line conductor and a neutral conductor in the event of a ground fault on either conductor of predetermined impedance characteristics, said device comprising, in combination:
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A. circuit interrupting contacts for connection in series with the line conductors; B. a trip solenoid operating, when energized, to initiate separation of said contacts and interruption of current flow in the distribution circuit; C. a differential current transformer including 1. a first primary winding for connection in series with the line conductor, 2. a second primary winding for connection in series with the neutral conductor, and 3. a secondary winding in which is developed a secondary current proportional to the imbalance in the currents flowing in said first and second primary windings; D. an output element connected across said differential transformer secondary winding; E. a normally conductive electronic switch connected across said differential transformer secondary winding in shunt with said output element; F. a neutral transformer having a secondary winding for connection in series with the neutral conductor and a primary winding; G. a pulse generator connected to supply a periodic pulse output through said primary winding of said neutral transformer to render said switch non-conductive for the interval of said pulse and thereby divert said secondary current through said output element pursuant to developing a trip signal voltage thereacross; and H. a signal processor processing said trip signal voltage and initiating energization of said trip solenoid in the event the amplitude of the signal voltage exceeds a predetermined minimum. - View Dependent Claims (5, 6, 7, 8)
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Specification