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A novel digital distance scheme has been implemented on a 32-bit digital signal processor board. The scheme is tested on a physical model of double circuit lines of equal impedance with a source at each end. Two relays instead of four are proposed for the two lines. Each relay is fed by three voltage and six current signals. The technique is based on the comparison of the measured impedance of the corresponding phases. Tests conducted on the physical model for various faults show that high fault resistance, current in-feed, balance-point location, out-of-step operation, and far-end faults are solved. Moreover, 100% of the line is protected.
Date of Publication: Oct. 2004