Control circuit for resetting drawout circuit breaker UVR solenoid

Claim 1

A circuit for controlling an undervoltage release (UVR) solenoid having a plunger mechanically operative to trip a circuit breaker in response to a system undervoltage condition, said control circuit including, in combination: A. first and second buses having input ends coupled with an electrical distribution system for developing thereacross a DC control voltage proportional to the system voltage; B. a first control relay having an operating coil connected between said first and second buses to be picked up by said control voltage so long as said system voltage remains above a predetermined minimum level, said first control relay further including normally open first contacts connected in said first bus downstream from its operating coil; C. a dropping resistor connected in series with the UVR operating solenoid coil across said first and second buses downstream from said first control relay contacts, whereby the pickup of said first control relay closes its first contacts to apply said control voltage across the series combination of said dropping resistor and UVR solenoid coil pursuant to developing sufficient holding voltage across the UVR solenoid coil to magnetically hold its plunger in a reset position and thus preclude tripping of the circuit breaker; D. a UVR solenoid drop-out delay including an energy storage capacitor connected across said first and second buses downstream from said first control relay contacts to be charged by said DC control voltage while said first control relay is picked up and its first contacts closed, whereby upon drop-out of said first control relay in response to the system voltage falling below said predetermined minimum level, said energy storage capacitor discharges through the UVR solenoid coil to develop sufficient holding voltage to hold the plunger in its reset position for a predetermined duration pending restoration of normal system voltage; and E. a UVR solenoid resetting network including (1) a second control relay having an operating coil and normally open contacts connected in shunt with said dropping resistor, (2) a timer connected with said second control relay operating coil to effect the pickup of said second control relay for a pre-selected time interval in response to an initiating signal; (3) first means connected with said first and second buses downstream from said first control relay contacts for developing said timer initiating signal in response to the pickup of said first control relay following the dropout thereof in response to a system undervoltage condition, and (4) second means connected with said first and second buses downstream from said first control relay contacts for developing said timer initiating signal in response to the reconnection of the UVR solenoid into said control circuit while said first control relay is picked up following the disconnection therefrom as occurring on occasion when the circuit breaker is installed in a drawout configuration, (5) whereby, said second control relay is picked up under the control of said timer acting in response to said initiating signal to close said contacts thereof and thus shunt said dropping resistor for said pre-selected time interval such that virtually the full magnitude of said DC control voltage is applied across the UVR operating coil to develop sufficient magnetic attraction to draw the UVR solenoid plunger from its trip initiating, extended position back to its reset position.