Circuit arrangements for detecting phase unbalance

Claim 1

AN ELECTRIC CIRCUIT ARRANGEMENT SUITABLE FOR DETECTING UNBALANCE BETWEEN THE RESPECTIVE PHASE CURRENTS CARRIED BY CONDUCTORS CONNECTED BETWEEN A POLYPHASE A.C. SUPPLY AND A LOAD, SAID ARRANGEMENT INCLUDING FOR EACH RESISTOR IS SMOOTHED TO PROVIDE A D.C. SIGNAL PROPORMARY WINDING OF WHICH IS ENERGISABLE BY THE PHASE CURRENT, A FULL WAVE RECTIFIER CONNECTED TO THE SECONDARY WINDING OF THE TRANSFORMER AND A RESISTOR CONNECTED ACROSS THE OUTPUT OF THE RECTIFIER TO SERVE AS A BURDEN TO THE TRANSFORMER AND A LOGIC CIRCUIT HAVING A PLURALITY OF INPUT PATHS ONE FOR EACH PHASE OF THE SUPPLY, AND AN OUTPUT PATH, AND WHEREIN IN USE THE VOLTAGE DEVELOPED ACROSS EACH RESISTOR IS SMOOTHED TO PROVIDE A D.C. SIGNAL PROPORTIONAL TO THE MEAN VALUE OF THE PHASE CURRENT, SAID SIGNALS ARE APPLIED TO RESPECTIVE INPUT PATHS OF SAID LOGIC CIRCUIT, AND A FURTHER D.C. SIGNAL IS DEVELOPED AT THE OUTPUT PATH OF THE LOGIC CIRCUIT WHEN THERE IS A DIFFERENCE BETWEEN ANY TWO OF THE D.C. SIGNALS, SAID FURTHER SIGNAL BEING PROPORTIONAL TO THE DIFFERENCE BETWEEN THE TWO D.C. SIGNALS HAVING THE HIGHEST AND LOWEST VALUES RESPECTIVELY AND MEANS UTILISING SAID FURTHER SIGNAL OR A SIGNAL DERIVED THEREFROM TO INDICATE THE PRESENCE OF UNBALANCE BETWEEN THE PHASE CURRENTS.