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This paper presents a fault detection and faulty area identification algorithm in double-circuit transmission lines (DCTLs) compensated by the generalized unified power flow controller (GUPFC) for the first time. The topology of the GUPFC-compensated DCTL is threatened by three types of faults: single-circuit faults, inter-circuit faults, and grounded double-circuit cross-country faults. In the first step, the suggested scheme can determine the time of fault in this type of topology using a very fast method that is based on the analysis of a current index called the current jump index. In the second step, the fault type and area are identified with the help of two other indices, i.e., voltage difference index and current difference index. The test network presented in this paper, which includes a DCTL and a GUPFC, along with the proposed algorithm, is implemented in the MATLAB software package. The results of the simulation and sensitivity analysis of the algorithm confirm the correct performance of the algorithm. [ABSTRACT FROM AUTHOR]

In the modern power systems operating at lower stability margins, conventional non-adaptive schemes cannot offer adequate protection for securing the power system, especially against combinational events. For major disturbances, the active power deficit is usually accompanied by reactive power deficit and frequency stability and voltage stability of the system are jeopardized simultaneously. In this paper, three adaptive combinational load shedding methods are proposed to improve operation of the conventional underfrequency load shedding scheme in order to enhance power system stability following severe disturbances. The proposed methods use locally measured frequency and voltage signals to counteract such events. In the proposed algorithms, load shedding is started from the locations which have higher voltage decay for longer period of time. The speed, location, and amount of load shedding are changed adaptively depending on the disturbance location, voltage status of the system, and the rate of frequency decline. Operation of the conventional and the proposed load shedding methods have been simulated in an actual large network. Obtained simulation results confirm that the proposed methods provide considerable enhancement in the power system voltage stability margin, and by using the proposed algorithms, various power system blackouts could be prevented. [ABSTRACT FROM AUTHOR]

• Fault location (FL) algorithm for three-terminal series capacitor compensated lines. • Phasor-based FL equations derived for different fault types in any line section. • Fault location using asynchronously measured phasors at all three terminals. • Independent of the parameters of series capacitor compensator and its protections. • Not requiring a high sampling rate or training process for implementation. In this study, a new algorithm for fault location in series capacitor compensated three-terminal transmission lines using the distributed line model is proposed. The proposed algorithm uses the sampled data of currents and voltages of all the three terminals, which are transferred asynchronously using telecommunication lines. All data transmission delays are calculated in terms of line parameters as well as the measured values of currents and voltages of the three terminals. Based on the data received from the three terminals, current and voltage equations of different points of the network are constituted for different types of faults. By solving these equations according to their boundary conditions, accurate locations of faults are estimated. One of the salient features of the suggested algorithm is that the schemed equations are independent of the model of the series capacitor compensator during fault occurrence and its protective circuitry. Also, based on the sensitivity analyses performed in this paper, the presented algorithm works perfectly against the errors caused by measurements and parameters. The test system and the suggested algorithm were realized in MATLAB environment. The obtained simulation results for different fault types occurring in various places in the line verify the accurate performance of the algorithm. [ABSTRACT FROM AUTHOR]

The high penetration of Renewable Energy Sources into electric networks shows new perspectives for the network's management: among others, exploiting them as resources for network's security in emergency situations. The paper focuses on the frequency stability of a portion of the grid when it remains islanded following a major fault. It proposes an optimization algorithm that considers the frequency reaction of the relevant components and minimizes the total costs of their shedding. The algorithm predicts the final frequency of the island and the active power profiles of the remaining generators and demands. It is formulated as a Mixed-Integer Non-Linear Programming problem and the high computation time due to a large-size problem is mitigated through a simplified linear version of the model that filters the integer variables. The algorithm is designed to operate on-line and preventively compute the optimal shedding actions to be engaged when islanding occurs. The algorithm is validated for a typical distribution grid: the minimum amount of shedding actions is obtained while the most frequency reactive resources are maintained in operation to assure a feasible frequency. Finally, time-domain simulations show that the optimal solution corresponds to the one at the end of the network's transients following the islanding. [ABSTRACT FROM AUTHOR]