Means for determining the self or earth impedance of an electric supply system by producing an indication when the magnitude of the current exceeds that for the maximum permissible impedance

Claim 1

A DEVICE FOR TESTING THE IMPEDANCE OF THE WHOLE FAULT CURRENT PATH BETWEEN TWO SELECTED POINTS OF AN ALTERNATING CURRENT ELECTRICITY SUPPLY SYSTEM WHILE IT IS ENERGISED FROM THE MAIN SUPPLY SOURCE COMPRISING A SILICON CONTROLLED RECTIFIER, A LOAD RESISTOR OF VERY LOW VALUE, CONNECTIONS PLACING SAID RECTIFIER IN SERIES WITH SAID LOAD RESISTOR ACROSS SAID SELECTED POINTS SO THAT SHORT-CIRCUIT CONDITIONS WILL RAISE WHENEVER SAID RECTIFIER IS CAUSED TO CONDUCT CURRENT, A CAPACITOR, CHARGING MEANS NORMALLY CONNECTED TO SAID CAPACITOR TO CHANGE THE SAME WITH ENERGY FROM SAID SUPPLY SYSTEM, MANUALLY OPERABLE MEANS FOR DISCONNECTING SAID CAPACITOR FROM SAID CHARGING MEANS ANMD CONNECTING IT TO SAID RECTIFIER TO INJECT ITS STORED ENERGY THEREINTO AS AN INSOLATED CURRENT PULSE ADAPTED TO CAUSE SAID RECTIFIER TO CONDUCT HEAVY CURRENT FOR A VERY BRIEF SPACE OF TIME, THE PASSAGE OF THE RESULTANT PULSE OF HEAVY CURRENT THROUGH SAID LOAD RESISTOR CAUSING THE DEVELOPMENT ACROSS SAID RESISTOR OF AN IMPEDANCE-INDICATING POTENTIAL DIFFERENCE REPRESENTATIVE OF THE IMPEDANCE OF THE FAULT CURRENT PATH BETWEEN SAID SELECTED POINTS MEANS OPERABLE TO PRE-SELECT ANY ONE OF A NUMBER OF PREDETERMINED DIFFERENT PROPORTIONS OF SAID IMPEDANCEINDICATING POTENTIAL DIFFERENCE WHICH PROPORTIONS EACH CORRESPOND TO A DIFFERENT FUSE RATING OF THE SYSTEM UNDER TEST, A THYRATRON FROM OF VOLTAGE RESPONSIVE INDICATING DEVICE OPERABLE TO PRODUCE A PERSISTING INDICATION UPON THE APPLICATION THERETO OF A POTENTIAL DIFFERENCE OF A PREDETERMINED MAGNITUDE AND MEANS FOR APPLYING SAID PRESELECTED PROPORTION OF SAID IMPEDANCE-INDICATING POTENTIAL DIFFERENCE TO THE GRID OF SAID THYRATRON FORM OF VOLTAGE RESPONSIVE INDICATING DEVICE TO PRODUCE A PERSISTING INDICATION WHENEVER SAID APPLIED PROPORTION OF SAID IMPEDANCE-INDICATING POTENTIAL DIFFERENCE AT LEAST REACHES SAID PREDETERMINED MAGNITUDE.