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This paper revisits the generalized alpha plane (GAP) formulation applied to differential protection of multi-terminal apparatus. The GAP formulation is improved by aiming for three main goals: 1) control over the internal fault settlement region (FSR); 2) enabling a simple operation characteristic instead of a restraint characteristic; and, 3) The adjustments are not dependent to the device type. For this purpose, the GAP formulation is redefined in terms of two settings, which transform the FSR into a circumference with a controllable center and radius. Thereby, a circular operation characteristic with an adjustable radius is enabled around the FSR, for to improve security. To validate and test the performance of the improved GAP, numerous computer simulations have been carried out using Alternative Transients Program on different multi-terminal equipment (i.e., busbars, transmission lines, and power transformers). Furthermore, massive data analysis is held as a means to highlight the GAP's sensibility. The obtained results demonstrate a well-stable pre-fault point, a consistent circular FSR, and the effectiveness of the improved GAP even under severe conditions. [ABSTRACT FROM AUTHOR]

Highlights • A new power transformer differential protection based on the instantaneous-current-value negative sequence is proposed. • The ratio of the operating and restraint negative sequence current signals is integrated during the time. • A new harmonic restraint strategy is also proposed, to improve protection security for external faults with CT saturation. • The proposed method is able to detect turn-to-turn and turn-to-ground faults. • The proposed algorithm may be more sensitive and faster than the traditional differential elements. Abstract This paper proposes a new algorithm for power transformer differential protection based on the instantaneous-current-value negative sequence current signals, which are reconstructed in discrete time-domain from the negative sequence phasor for the different transformer windings. Aiming to provide a more reliable operation of the proposed method, the ratio of the operating and restraint negative sequence current signals is integrated during the time. Also, as a by product, a new instantaneous-current-value harmonic restraint strategy is also proposed, to improve protection security for external faults with current transformer (CT) saturation. In order to evaluate the performance of the proposed algorithm, a wide variety of faults are simulated in the Alternative Transients Program (ATP) by varying the fault type; short-circuited turns percentage; sources strength and the power system loading. The obtained results reveal that the proposed method is able to detect turn-to-turn and turn-to-ground faults even for 1% of short-circuited turns, in such way that it may be more sensitive and faster than the traditional differential elements widespread used by manufacturers in real world protection applications. Therefore, the developed algorithm is an excellent complement to the conventional differential functions, for the most faster and sensitive operations for internal faults involving few turns, and safe for external short circuits with CT saturation. [ABSTRACT FROM AUTHOR]

• The current mapping strategy (CMS) can improve the performance of differential protection of series-compensated transmission lines compared to the regular alpha plane. • The protection engineer can adjust the CMS according to the desired emphasis (i.e., sensitivity or security). • The CMS operates correctly even under severe outfeed conditions or subsynchronous oscillations. • Transient studies and 1340 simulations with different pre-fault and fault conditions proved the effectiveness of the CMS. This paper presents a particular case of the generalized alpha plane called current mapping strategy (CMS) formulation applied to differential protection of series-compensated transmission lines. The proposed formulation presents two unique features, control over the internal fault settlement region (FSR) and the use of an operation characteristic (OC). The FSR and the OC are two concentric circles defined on the alpha plane. Additionally, the proposed CMS allows the user to adjust the center and radius of the FSR and OC, according to the desired sensitivity and security of the protection. To validate and test the performance of the improved CMS, numerous computer simulations have been carried out using the Alternative Transients Program (ATP) on a 400 km long series-compensated, 500-kV transmission line. Furthermore, analysis of an extensive database of cases is conducted to highlight the CMS's sensitivity. The obtained results demonstrate the effectiveness of the settings of the CMS and a smooth trajectory to the FSR. The CMS also proved to be stable and reliable even under severe subsynchronous oscillations and outfeed conditions. [ABSTRACT FROM AUTHOR]