Root mean square measuring device for negative sequence current

Details Root mean square measuring device for negative sequence current Root mean square measuring device for negative sequence current

G - Physics

01

R

324/29

G01R 29/16 (2006.01) H02H 3/34 (2006.01)

Patent

CA 1237474

- 16 - ABSTRACT OF THE DISCLOSURE To protect electrical three-phase machines from damage on the appearance of an unbalanced load between the phases, so-called negative sequence current protection is used. Conventional measurement of the negative sequence current takes place in filters which contain frequency dependent LC components. Frequency variations in a three- phase supply, because of an unbalanced frequency response for harmonics in the three phase filters, may lead to an erroneous indication of negative sequence current. The invention provides a novel method for determining both the positive sequence and the negative sequence currents to a three-phase load. For grounded systems the zero-sequence current is eliminated.Measuring each phase current (IR , IS , IT) and the phase sequence, the positive sequence and/or negative sequence current are/is determined as the solution of an equation derived in advance from the electrical relationships between the phase currents. The invention also relates to a device for carrying out the method.

473681

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