Ground fault protective systems with predetection neutralization of reactive currents
First Claim
1. A ground fault protective system for use with a power distribution system for supplying a.c. power to a known load from at least two supply conductors, at least one of said supply conductors exhibiting a measureable downstream reactance to ground giving rise to net reactive differential currents in said supply conductors not characteristic of a real ground fault comprising:
- differential current sensing means responsive to currents in said supply conductors for generating fault signals representing differential currents carried by said supply conductors; and
neutralizing means comprising at least one auxiliary circuit branch including predetermined impedance means so connected to at least one of said supply conductors and proportioned relative to said downstream reactance to ground as to exert a neutralizing effect on said net reactive differential currents substantially counterbalancing the effect on said fault signals of said downstream reactance to ground.
0 Assignments
0 Petitions
Accused Products
Abstract
Ground fault protective systems are disclosed in which fault signals are generated in response to differential currents carried by electrical supply lines. A circuit breaker interrupts power on the supply lines when the fault signals exceed a given magnitude and duration. Downstream reactances to ground from one or more supply lines give rise to spurious fault signals which do not characterize true ground fault conditions. These spurious fault signals are cancelled prior to detection by means of neutralizing auxiliary circuits. The resulting fault signals exhibit a high signal-to-noise ratio.
29 Citations
12 Claims
-
1. A ground fault protective system for use with a power distribution system for supplying a.c. power to a known load from at least two supply conductors, at least one of said supply conductors exhibiting a measureable downstream reactance to ground giving rise to net reactive differential currents in said supply conductors not characteristic of a real ground fault comprising:
-
differential current sensing means responsive to currents in said supply conductors for generating fault signals representing differential currents carried by said supply conductors; and neutralizing means comprising at least one auxiliary circuit branch including predetermined impedance means so connected to at least one of said supply conductors and proportioned relative to said downstream reactance to ground as to exert a neutralizing effect on said net reactive differential currents substantially counterbalancing the effect on said fault signals of said downstream reactance to ground. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
-
-
10. A ground fault protective system for use with a power distribution system for supplying a.c. power to a known load from at least two supply conductors, at least one of said supply conductors exhibiting a measurable capacitance to ground, comprising:
-
differential current sensing means comprising a magnetic core structure having a plurality of primary windings inductively associated therewith, each connected in series with one of said supply conductors, and at least one secondary winding thereon for generating ground-fault-characterizing signals in response to net magnetic fluxes induced in said core structure as a result of differential currents in said primary windings; circuit breaker means for interrupting continuity in said supply conductors; detector means having an output circuit for tripping said circuit breaker and an input circuit for receiving fault signals from said secondary winding; and means for minimizing spurious signals in said secondary winding as a result of said stray capacitance from one of such supply conductors to ground, comprising auxiliary circuit means having balancing capacitance therein proportioned to the value of said measurable capacitance and so connected to at least one of said supply conductors as to result in an ampere-turn influence on said core structure substantially equal and opposite to the effect thereon of said measurable capacitance to ground.
-
-
11. A ground fault protective system for use with a power distribution system for supplying a.c. power to a known load from at least two supply conductors, at least one of said supply conductors exhibiting a measurable stray capacitance to ground, comprising:
-
differential current sensing means comprising a magnetic core structure having a plurality of primary windings inductively associated therewith, each connected in series with one of said supply conductors, and at least one secondary winding thereon for generating ground-fault-characterizing signals in response to net magnetic fluxes induced in said core structure as a result of differential currents in said primary windings; circuit breaker means for interrupting continuity in said supply conductors; detector means having an output circuit for tripping said circuit breaker and an input circuit for receiving fault signals from said secondary winding; and means for cancelling spurious signals induced in said secondary winding as a result of said stray capacitance from one of such supply conductors to ground, comprising an auxiliary circuit branch having a balancing resistance therein proportioned to the reactance of said stray capacitance and so connected between said one supply conductor and the input circuit of said detector to neutralize said spurious signals prior to their introduction into said detector means.
-
-
12. A ground fault protective system for use with a power distribution system for supplying a.c. power to a known load from polyphase supply conductors, at least one of said supply conductors exhibiting a measurable stray capacitance to ground, comprising:
-
differential current sensing means comprising a magnetic core structure having a plurality of primary windings inductively associated therewith, each connected in series with one of said supply conductors, and at least one secondary winding thereon for generating ground-fault-characterizing signals in response to net magnetic fluxes induced in said core structure as a result of differential currents in said primary windings; circuit breaker means for interrupting continuity in said supply conductors; detector means having an output circuit for tripping said circuit breaker and an input circuit for receiving fault signals from said secondary winding; and means for minimizing spurious signals in said secondary winding as a result of said stray capacitance from such supply conductors to ground, comprising an auxiliary circuit branch having a balancing capacitance therein proportioned to the net imbalance of said stray capacitance and so connected between at least one of said supply conductors and ground downstream of said differential sensing means as to result in a ratio of voltage to capacitive impedance to ground on one ungrounded supply conductor substantially equal to the ratio of voltage to capacitive impedance to ground on each of the other supply conductors.
-
Specification