Phase condition indicating circuit

Claim 1

A circuit for indicating unbalance between the phases in a three phase input three wire alternating current electrical line system operating at a set frequency, said circuit comprising a current transformer having an iron alloy core, primary and secondary windings for respectively connecting the three phase inputs to the indicating circuit, resistance means and capacitive means connected across said secondary windings and having an alternating current voltage appearing thereacross, said current transformer providing a first undistorted output at a first level and a second distorted output at a second level, and a threshold region existing between said first and second levels, said resistance means comprising a resistance wherein the output voltage appearing thereacross is in said threshold region, said capacitor means having a capacity less than the resonant value for the set frequency thereby to maintain a linear voltage-tocurrent relation from essentially a zero current to the current transformer saturation level at about the ten ampere input current level, means for developing an artificial neutral reference, means for developing signals proportional to the deviation of any of said phase inputs from said reference, means for developing signals proportional to the relative amplitudes of the various phase inputs, means for comparing said developed signals against selected levels, and means responsive to the energization of said comparing means thereby to indicate nonnormal phase conditions.