Patent ID: 8451574
Filing Date: 2013-05-28
Classification: G01R,H02H

Abstract:
1. A method for fault detection analysis in a power device positioned along a power line having one or more phases which is operatively associated with a differential protection unit, said power device having at least one input side and one output side through which an input current flows into the power device and an output current flows out from the power device, respectively, the method comprising for each of said one or more phases of said power line: generating a first signal and a second signal which are each representative of said input current flowing on said power line for an associated one of said one or more phases of said power line, and a third signal and a fourth signal which are each representative of said output current flowing on said power line for said one or more phases of said power line for which said first and second signals are generated, wherein said first signal and said second signal are constituted by the magnitude of a first current phasor representing said input current and the change of the magnitude of said first current phasor in a determined period of time, respectively, and wherein said third signal and said fourth signal are constituted by the magnitude of a second current phasor representing said output current and the change of magnitude of said second current phasor in a determined period of time, respectively; generating a fifth signal and a sixth signal which are each representative of a relationship between said input current flowing on said power line for said associated one of said one or more phases of said power line for which said first and second signals are generated and said output current flowing on said power line for said associated one of said one or more phases of said power line for which said first and second signals are generated, wherein said fifth signal is representative of the phase angle α formed between a first current phasor representing said input current and a second current phasor representing said output current, the first current phasor being taken as reference, and wherein said sixth signal represents the magnitude of a phasor obtained by summing a first current phasor representing said input current and a second current phasor representing said output current; comparing said first signal and said third signal with a first threshold and said fifth signal with a second threshold expressed in terms of angular values, and when said first signal and said third signal exceed said first threshold and said fifth signal exceeds said second threshold at the same time, producing a first output signal indicative of a potential fault external for said associated one of said one or more phases of said power line for which said first and second signals are generated to the power device; comparing said second signal and said fourth signal with a third threshold and said sixth signal with a fourth threshold, and when said second signal and said fourth signal exceed said third threshold and said sixth signal exceeds said fourth threshold at the same time, producing a second output signal indicative of a potential fault for said associated one of said one or more phases of said power line for which said first and second signals are generated external to the power device; and when at least one of said first output signal for said associated one of said one or more phases of said power line for which said first and second signals are generated and said second output signal associated with said first output signal indicative of a potential fault external to the power device is still present after a predetermined period of time is elapsed, generating a disabling signal for said associated one of said one or more phases of said power line for which said first and second signals are generated so as to temporarily disable said differential protection unit.