Patent ID: 6507184
Filing Date: 2003-01-14
Classification: G01R,H02H

Abstract:
A method for measuring the differential current between a first terminal of a device in a three-phase power system and a second terminal of the device, wherein the device introduces a phase shift between said first and second terminals on each phase of the power system, the method comprising:obtaining, for each phase, a measure of the current through the first terminal of the device and a measure of the current through the second terminal of the device; normalizing the measured currents of each phase of the first and second terminals in order to compensate for changes in at least one of phase and magnitude introduced by the device, said normalization being performed in accordance with the following transformation: G(&thgr;)=cos(&thgr;)U+sin(&thgr;)J where G( ) is a generalized normalization transform comprising a quadrature combination of U and J, U represents a unit zero degree phase shift with zero sequence components removed, and J represents a unit ninety degree phase shift with zero sequence components removed; andcalculating from the normalized measured currents a differential current for each phase.