Time delay extender for static relays

Claim 2

A static relay comprising: a a current-sensing circuit; b. a charging network connected to said current-sensing circuit said charging network having input terminals connected to said current-sensing circuit, and output terminals; the voltage at said output terminals increasing with time according to a predetermined curve after said current-sensing circuit is connected to said input terminals of said charging network; c. pickup circuit means connected between said current-sensing circuit and said input terminals of said charging network; said pickup circuit means energizing said input terminals of said charging network when the output of said current-sensing means exceeds a predetermined value; d. output circuit means connected to said output terminals of said charging network and being energized when the output of said output terminals exceeds a predetermined value; e. and continuously operating switching circuit means operating between a first impedance condition and a second impedance condition at a given operating frequency with said first and second impedance conditions lasting for respective given lengths of time independently of the output of said currentsensing circuit; said continuously operating switching means connected to said input terminals of said charging network and preventing the charging of said charging network from said current-sensing circuit when said switching means is in its said first impedance condition, thereby to increase the effective time constant of said charging network.

Claim 3

The relay of claim 1 wherein said charging network consists of a resistor-capacitor network.

Claim 4

The relay of claim 1 wherein said switching circuit means comprises a free running multivibrator.

Claim 5

The relay of claim 2 wherein said switching circuit means is connected in parallel with the capacitors of said resistor-capacitor network.

Claim 6

For use in protecting current distribution networks, static overcurrent relay means responsive to overcurrent conditions for operating circuit protective devices after a predetermined time period and before the network is damaged comprising first means for generating a DC voltage representative of the current being monitored in said network; second means coupled to said first means for generating a predetermined voltage level after a predetermined time delay; third means coupled to said first means and normally inhibiting the operation of said seconD means until the output voltage level of said first means achieves a predetermined magnitude; constant voltage reference means coupled to the output of said first means for establishing a second predetermined threshold level; fourth voltage-sensitive switch means coupled to said second means and said constant voltage reference means for energizing a circuit protective device when the output voltage of said second means achieves said second predetermined threshold level; and continuously operating switching circuit means operating between a high impedance condition and a low impedance condition at a given operating frequency with said high and low impedance conditions lasting for respective given lengths of time independently of the output of said first means; said continuously operating switching means connected to said second means and permitting the energization of said second means only when said switching means is in its said high impedance condition, thereby to increase the effective time constant of said second means.

Claim 7

For use in protecting current distribution networks, static overcurrent relay means responsive to overcurrent conditions for operating circuit protective devices after a predetermined time period and before the network is damaged comprising first means for generating a DC voltage representative of the current being monitored in said network; second means coupled to said first means for generating a predetermined voltage level after a predetermined time delay; third means coupled to said first means and normally inhibiting the operation of said seconD means until the output voltage level of said first means achieves a predetermined magnitude; constant voltage reference means coupled to the output of said first means for establishing a second predetermined threshold level; fourth voltage-sensitive switch means coupled to said second means and said constant voltage reference means for energizing a circuit protective device when the output voltage of said second means achieves said second predetermined threshold level; and continuously operating switching circuit means operating between a high impedance condition and a low impedance condition at a given operating frequency with said high and low impedance conditions lasting for respective given lengths of time independently of the output of said first means; said continuously operating switching means connected to said second means and permitting the energization of said second means only when said switching means is in its said high impedance condition, thereby to increase the effective time constant of said second means.

Claim 8

For use in protecting current distribution networks, static overcurrent relay means responsive to overcurrent conditions for operating circuit protective devices after a predetermined time period and before the network is damaged, comprising: first means for generating a DC voltage representative of the current being monitored in said network; second means coupled to said first means for generating a predetermined voltage level after a predetermined time delay; third means coupled to said first means and normally inhibiting the operation of said second means until the output voltage level of said first means achieves a predetermined magnitude; fourth means coupled to said second means for energizing a circuit protective device when the output voltage of said second means achieves a second predetermined magnitude; said first means being comprised of current transformer means, and full wave rectification means connected across the output of said current transformer means for generating said DC voltage; said second means being comprised of a passive network of resistive and reactive elements for generating the desired time delay substantially in accordance with the equation where: V0 is the output voltage of said timing circuit; V1 is the input voltage to said timing circuit; t is elapsed time; and where T1 time constant of the timing circuit; and continuously operating switching circuit means operating between a first impedance condition and a second impedance condition at a given operating frequency with said first and second impedance conditions lasting for respective given lengths of time independently of the output of said first means; said continuously operating switching means connected to said second means and permitting the energization of said second means only when said switching means is in its said high impedance condition, thereby to increase the effective time constant of said second means.

Claim 9

For use in protecting current distribution networks, static overcurrent relay means responsive to overcurrent conditions for operating circuit protective devices after a predetermined time period and before the network is damaged, comprising: first means for generating a DC voltage representative of the current being monitored in said network; second means coupled to said first means for generating a predetermined voltage level after a predetermined time delay; third means coupled to said first means and normally inhibiting the operation of said second means until the output voltage level of said first means achieves a predetermined magnitude; fourth means coupled to said second means for energizing a circuit protective device when the output voltage of said second means achieves a second predetermined magnitude; said first means being comprised of current transformer means, and full wave rectification means connected across the output of said current transformer means for generating said DC voltage; said second means being comprised of a passive network of resistive and reactive elements for generating the desired time delay substantially in accordance with the equation where: V0 is the output voltage of said timing circuit; V1 is the input voltage to said timing circuit; t is elapsed time; and where T1 time constant of the timing circuit; and continuously operating switching circuit means operating between a first impedance condition and a second impedance condition at a given operating frequency with said first and second impedance conditions lasting for respective given lengths of time independently of the output of said first means; said continuously operating switching means connected to said second means and permitting the energization of said second means only when said switching means is in its said high impedance condition, thereby to increase the effective time constant of said second means.