Mutual inductor current sensor

Claim 1

In a three phase ac line having a ground and in which positive, negative and zero sequence currents can exist for providing power to an electrical load, a three phase current sensor for providing a signal indicative of the three phase current and phase imbalance of the load, comprising: an electrically insulated, current carrying conductor for each phase with one end of each conductor forming a line side connection and the other end of each conductor forming a load side connection, each conductor having a substantially U-shaped configuration having leg portions and a bight portion, the conductors positioned proximate one another and having the bight portions thereof overlapping forming a cylindrical cup having a bottom portion and a wall portion, the bottom portion formed by the bight portions of the conductors and the wall portion formed by the leg portions of the conductors, the leg portions of each of the conductors being substantially parallel to a longitudinal axis of the cup and radially positioned approximately 60 degrees from the leg portions of the other conductors in the cup; signal generator means positioned within the cup and including a pair of magnetic sensors positioned substantially parallel to and centered about the longitudinal axis of the cup and substantially orthogonal with respect to one another for sensing a magnetic field produced by a current flow in the conductors of the cup, the sensors of the signal generator means producing outputs that when squared and summed have a dc term indicative of the sum of the squares of the currents flowing in the conductors of the cup and an ac term indicative of the phase imbalance whereby processing of the dc and ac terms of the output results in the dc term being substantially proportional to the average value of the sum of the squares of the current flowing in the conductors and the ac term being substantially at twice the frequency of the current and substantially proportional to the product of the positive and negative sequence currents; and Faraday shield means substantially enclosing the signal generator means and electrically connected to the ground, the Faraday shield means providing electrostatic shielding of the signal generator means.