Ground leakage differential protective apparatus

Abstract

A ground leakage differential current protective apparatus of the differential transformer type. An impedance is inserted in the grounded neutral line in series with the transformer and the load. A low impedance ground in the grounded neutral conductor still permits a potential to be developed across the grounded neutral winding so that the differential current required to initiate the tripping action is not substantially increased.

What we claim as new and desire to secure by Letters Patent of the United States is:  .[.1. An electrical load circuit protective device comprising: differential transformer means having first and second primary windings in series, respectively, with the line and neutral conductors supplying a load; circuit interrupting means in said line conductor responsive to unbalanced current flow in said primary windings to open said line conductor; and an inductance in said neutral conductor in series with said second primary winding..]..[. .[.2. The device of claim 1 wherein said inductance comprises an auxiliary transformer having an auxiliary primary winding energized from said line conductor and a secondary winding, said secondary winding being in series with said second primary winding and having a polarity in series opposition therewith..]. .[.3. The device of claim 2 wherein said auxiliary primary winding is in series with said first primary winding..]. .[.4. The device of claim 2 wherein said auxiliary primary winding is connected across said line and neutral 
     
        conductors..]. .[.5. The device of claim 1 wherein one end of each of said first and second primary windings is connected, respectively, to first and second input terminals and wherein said circuit interrupting means and said inductance are connected, respectively, in series with first and second output terminals..]..Iadd. 6. An electrical load circuit protective device comprising: differential transformer means having first and second primary windings in series, respectively, with the line and neutral conductors supplying a load; circuit interrupting means in said line conductor responsive to unbalanced current flow in said primary windings to open said line conductor; and an auxiliary transformer having first and second windings in the line and neutral conductors respectively, and connectable through the load in series-aiding relationship. .Iaddend.