Protective arrangement for an electric circuit breaker

Claim 1

IN COMBINATION WITH AN ELECTRIC CIRCUIT BREAKER HAVING A BUS TERMINAL AND A LINE TERMINAL, (A) A GAP DEVICE LOCATED EXTERNALLY OF SAID CIRCUIT BREAKER AND ELECTRICALLY CONNECTED BETWEEN SAID LINE TERMINAL AND GROUND, (B) SAID GAP DEVICE NORMALLY HAVING A SPARKOVER VOLTAGE AT A FIRST PREDETERMINED LEVEL THAT IS GREATER THAN THE PEAK VALUE OF SWITCHING SURGES TYPICALLY ENCOUNTERED AT SAID LINE TERMINAL, (C) CONTROL MEANS FOR VARYING THE SPARKOVER VOLTAGE OF SAID GAP DEVICE AND OPERABLE TO REDUCE THE SPARKOVER VOLTAGE OF SAID GAP DEVICE TO A SECOND PREDETERMINED LEVEL UPON INITIATION OF AN OPENING OPERATION OF SAID CIRCUIT BREAKER, (D) SAID SECOND PREDETERMINED LEVEL BEING SUFFICIENTLY LOW THAT WHEN THE CIRCUIT BREAKER IS OPEN ANY IMPULSE VOLTAGES REACHING SAID LINE TERMINAL THAT ARE HIGH ENOUGH TO SPARK OVER SAID GAP DEVICE WILL BE LIMITED IN VOLTAGE BY SUCH SPARKOVER TO VALUES WHICH, IN GENERAL, WILL BE INSUFFICIENT TO CAUSE AN ELECTRIC BREAKDOWN INTERNALLY OF SAID CIRCUIT BREAKER BETWEEN SAID LINE TERMINAL AND SAID BUS TERMINAL, EVEN DURING THE PORTION OF THE REDUCED DIELECTRIC STRENGTH PERIOD BEGINNING ABOUT 1/2 CYCLE AFTER THE INTERRUPTION OF CURRENTS NEAR THE MAXIMUM RATING OF SAID CIRCUIT BREAKER.