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The delayed operation of distance relays zone-2 element for the faults at the end of the line is excessive. It reduces the fault clearing speed and therefore, is one of the main factors that can endanger power system stability. This paper proposes an impedance-based scheme for discrimination between the last 20% of the line length faults and the adjacent line faults, which are covered by the relay zone-2. The suggested non-pilot scheme uses a modified fault location formula for the accelerated zone-2 operation of distance relays. The negative- and zero-sequence components of local signals are utilized to calculate the accurate fault location after the remote circuit breaker (CB) operation. The proposed algorithm is independent of fault resistance, power flow direction, pre-fault condition, and it can clearly distinguish internal faults from the adjacent line faults. Simulation results show that the proposed method can identify the remote CB operation and thus can accelerate the tripping of zone-2 within a very short time for different fault locations, fault types, fault resistances, and load angles. Also, accurate fault location has been achieved under all simulation conditions. [ABSTRACT FROM AUTHOR]

The fault resistance and infeeded currents from tapped transmission lines are the two main challenges to establish correct fault location estimation in multi-terminal transmission lines. Also, fault location estimation in double-circuit lines is more complicated than single-circuit lines due to the effect of mutual coupling and inter-circuit faults. This paper proposes a negative-sequence network-based method to estimate the fault location of double-circuit multi-terminal transmission lines. In the presented method, signals are measured in the relay location and then, communication links are not required as it uses only one end measurements. Also, in conventional distance relays, six elements are needed to calculate the fault location in all types of faults. Furthermore, in this method, by using only one element for each transmission line, accurate fault location can be estimated. Also, high fault resistance, mutual coupling, and infeeded currents from tapped transmission lines do not have impact on the performance of the presented scheme. To investigate the effects of the line shunt capacitances on the proposed method, a PI model of the transmission lines is used in all the investigations. Simulation results carried out using MATLAB software indicate that the proposed scheme is able to produce excellent performance for the fault location estimation. [ABSTRACT FROM AUTHOR]

The existence of a generalized interline power-flow controller (GIPFC) in the transmission lines changes the voltage and current signals which are measured with the protection relays of power system dynamically. In this paper, the effects of the GIPFC on the measured impedance by the loss of excitation (LOE) relay of the synchronous generator are first investigated by analytical and computational methods for different operating modes of the power system. The results indicate that the presence of GIPFC causes a substantial delay on the operation of the LOE relay. It is also shown that when partial LOE occurs, the GIPFC causes to the LOE relay under-reaching. Consequently, to readjust the relay in the presence of the GIPFC, a new modified LOE protection algorithm on the basis of synchronized phasor measurements received from phasor measurement units is presented. The most important advantage of this modified algorithm is that it is a general algorithm which considers all voltage-source-converter-based flexible ac transmission systems controllers. Regarding the simulations results, it is concluded that using the modified algorithm for the LOE relay can sufficiently decrease the delay and prevent the relay from under-reaching. The impacts of the unified power-flow controller and interline power-flow controller on the LOE relay are also demonstrated. [ABSTRACT FROM AUTHOR]

By utilizing multiline voltage-source (VSC)-based flexible ac transmission system (FACTS) controllers, independent controllability over each compensated line of a multiline system can be achieved. While VSC-based multiline FACTS controllers emerged as a new opportunity to control two independent ac systems, the main constraints and limitations that are presented to the conventional transmission-line protection systems need to be investigated. In this paper, the impacts of VSC-based FACTS controllers on distance relays while controlling the power flow of compensated lines are evaluated analytically and by detailed simulations for different fault types and locations. [ABSTRACT FROM PUBLISHER]