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• Accurate modeling of HPOTL considering electromagnetic coupling between AC and DC lines. • Simulating all types of faults in HPOTLs, including AC, DC and inter-system faults. • Complete investigation of induced components in AC and DC transmission lines in HPOTLs in different fault conditions with different fault resistances and locations. • Investigating the possibility of the impact of faults in one of the transmission lines (AC or DC) on the adjacent line protection system. • Investigating the most severe AC, DC and inter-system faults from the point of view of induction of voltage and current components in the adjacent line. The use of Hybrid Parallel HVAC/HVDC Overhead Transmission Lines (HPOTL) on the same tower can improve the power transfer capacity and transmission line stability and reduce power transient swing, but it will also present some challenges. The most important one is the electromagnetic coupling between the HVAC and HVDC lines due to the proximity of the lines. The electromagnetic coupling phenomenon induces different voltage and current components in the lines for different conditions, including the fundamental frequency component in the DC line and the zero sequence component in the AC line. The magnitude of the induced components is much higher in fault conditions than in normal conditions. The electromagnetic coupling between the HVDC and HVAC lines has a significant influence on their equipment and protection systems. In this paper, the induced components in the normal and various fault conditions in HPOTL are investigated with the detailed modeling of the HPOTL. In addition, the effect of faulty phase(s) or pole(s) for AC, DC, and AC/DC intersystem faults, fault location, and fault resistance on the induced component in transmission lines are investigated. Simulation results show that the electromagnetic coupling can cause the mal-operation of the protection system in healthy lines. [ABSTRACT FROM AUTHOR]

In this study, a dynamic state estimation (DSE) approach is proposed for power systems based on particle filter (PF) and ant colony optimisation for continuous domains (ACOR). Usually, the Kalman-based estimators with Gaussian noise assumption are utilised for DSE. However, this assumption is questionable for real power system data. Although PF methods offer a potential solution for this issue, the basic PF algorithm is time-consuming and suffers from sample impoverishment problem and degeneracy of the propagated samples. In this study, the search capability of ACORis utilised as an adaptive probability density function estimator to overcome these shortcomings and reduce the required particle numbers. The proposed approach minimises the computational effort by reducing the required particle numbers. The ninth-order model of the synchronous generator has been applied in this study. The performance of the proposed method is investigated through a two-area-four-machine test system as well as the IEEE 39-bus (New England) test system and it is compared with several advanced Kalman filter-based and PF-based approaches. The simulation results obtained for different case studies demonstrate the effectiveness and robustness of the proposed method against noises, abrupt state changes, and gross measurement errors. [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]

• Double-circuit grounded cross-country fault location in GUPFC-compensated DCTLs. • The proposed algorithm is independent of the GUPFC's operating point and parameters. • No GUPFC output current/voltage is measured in the proposed algorithm. • The algorithm is based on phasor theory; easily applicable in industrial relays. • The performance of the proposed method is very accurate and desirable. This paper presents an accurate fault location algorithm for double-circuit grounded cross-country (DCGCC) faults in double-circuit transmission lines (DCTLs) compensated by a generalized unified power flow controller (GUPFC). The algorithm incorporates synchronous current and voltage phasors at both end buses of the line. The proposed algorithm determines the accurate location of simultaneous faults occurring in both line circuits in three basic steps. In the first step, the faulty sections are identified using a zero-sequence current analysis. In the second step, the accurate location of a fault in the circuit on which only a series converter is installed is calculated. Next, by employing the calculated zero-sequence current of this fault point, the zero-sequence current component of the other line circuit, which is equipped with series and shunt converters, is obtained. Finally, the accurate fault location in this circuit is calculated. The calculation process and the derived equations for all DCGCC fault types are described in detail. The GUPFC considered in this study along with the test network is modeled in MATLAB/Simulink environment. The simulation results confirm the accurate performance of the proposed algorithm for various fault types occurring in different operating conditions. [ABSTRACT FROM AUTHOR]

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]

• Novel fault classification algorithm (FCA) for GUPFC-compensated transmission lines. • FCA is based on the loci of active and reactive powers calculated using PMU signals. • Presenting faulty area and faulty circuit detection algorithms using new indices. • The proposed method is robust and independent of the operating modes of the GUPFC. • Easily applicable in regular fault locators available in the protection industry. The paper presents a fault area detection and classification algorithm in the phasor domain for double-circuit lines compensated by a generalized unified power flow controller (GUPFC). In the first step, by defining and using a voltage index, the algorithm determines the side of the GUPFC in which the fault has occurred. In the second step, by defining and employing a current index, the algorithm will be able to identify the circuit of the line on which the fault has happened. Finally, the fault is classified. In this step, the algorithm detects the faulty phase by analyzing the loci of three-phase active and reactive powers at the line terminal. The algorithm uses the current and voltage phasors of the line terminals measured by the phasor measurement units (PMUs) in one cycle before and during the fault. The GUPFC and the test system have been modeled in MATLAB/Simulink. The presented algorithm is tested and evaluated under different conditions including different fault types and fault resistances for all normal series and shunt fault types. The results obtained from simulations verify the accurate performance of the algorithm for various fault conditions. [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]

An accurate inter‐circuit fault location algorithm for double‐circuit transmission lines compensated by a generalized unified power flow controller based on phasor analysis is presented. The proposed algorithm utilizes synchronous currents and voltages of the buses on both sides of the line to accurately calculate the fault location. Using the equations of sequence component circuits, the algorithm calculates voltage and current of the fault point on both circuits. Then, using boundary conditions equations for 98 types of inter‐circuit fault on the double‐circuit transmission lines, the accurate location of the fault is obtained. The number of boundary conditions equations varies depending on the type of faulty phases of the two circuits and the number of unknowns in the current and voltage equations of the fault point. The calculation of these boundary equations are also described. The results presented in the simulation section verify the validity and accurate performance of the proposed algorithm under different fault conditions. [ABSTRACT FROM AUTHOR]

Summary In this paper, a communication‐based selective protective scheme using the combined adaptive cumulative sum algorithm (CACUSUM) is proposed, which can be used in wide‐area protection of multi‐terminal high voltage direct current (MT‐HVDC) transmission lines. The proposed algorithm works in the time domain and uses the variation pattern of the magnitude of line currents and bus voltages for fault detection. Simulation is done in MATLAB program using a test four terminals meshed HVDC transmission system. As a robust fault detector, the proposed approach detects fault occurrence as well as determining faulty zone, either faults on the DC line or AC part of the HVDC system; the whole in less than 2 ms. Simulation results confirm the robustness of CACUSUM performance against different fault resistances and different fault locations as well as the presence of noise in the signals. Appropriate speed, adaptivity, independence from system parameters, low sampling rate, low computational burden, simplicity, no need for any complicated hardware, and ability to detect cross faults are the significant benefits of this method in comparison with other ones. [ABSTRACT FROM AUTHOR]

The rapid growth and development of manufacturing technology for controlling processors and high-power semiconductor devices has led to the enhancement of flexible AC transmission system (FACTS) controllers, thus improving the performance of power systems. The generalized unified power flow controller (GUPFC) is today introduced as the most advanced generation of the FACTS family, which is based on voltage source converter (VSC). It can, hence, control all the five parameters of a power system given above. The paper, for the first time, presents the accurate modeling of different parts of the control system and power electronics of the 72-pulse VSC-based GUPFC in detail to satisfy operation constraints and improve power quality in terms of harmonic level reduction. There is no need to use active or passive filters in the proposed model for reducing harmonic level of the GUPFC. In this regard, the calculation of four main parameters, namely D_alpha, alpha, angular speed, and sigma, as inputs of the pulse-firing system for the 72-pulse VSC is performed dynamically and optimally to meet all expected constraints in terms of operation, power quality, and harmonic reduction of a network with a GUPFC. The presented modeling is implemented on a 230 kV GUPFC-compensated double-circuit transmission line in MATLAB/Simulink environment, and the desired results of the presence of the 72-pulse VSC-based GUPFC are shown to meet the desired constraints of operators. [ABSTRACT FROM AUTHOR]

• Presenting a single end-based fault location method for hybrid parallel HVAC/HVDC overhead transmission lines (HPOTL). • Accurate modeling of HPOTL considering electromagnetic coupling between AC and DC lines. • Low sampling frequency and high accuracy in fault location estimation. • Determining the faulty half of transmission line using a robust method. • The proposed method is robust and independent of fault resistance, noise and fault angle. In this paper, a single ended traveling wave based fault location method is presented for Hybrid Parallel HVAC/HVDC Overhead Transmission Lines (HPOTLs) on the same tower using Discrete Wavelet Transform (DWT). In HPOTLs, the AC and DC transmission lines are adjacent to each other from the sending to the receiving end of the lines and there is electromagnetic coupling between them. Fault detection and classification algorithms in HPOTLs are presented in another paper. Therefore, in order to summarizing, in this paper, it is assumed that the fault is detected in the HVAC or/and HVDC lines and faulty line is identified. HPOTL faults include AC faults, DC faults and AC/DC intersystem faults. AC and DC voltage signals on sending end of the transmission line with a sampling frequency of 100 kHz are used for fault location in this paper. In order to minimize the noise effect, the squared wavelet transform coefficients (WTC2) is used for proposed fault location method. Finally, Bewley-Lattice diagrams are checked for the traveling wave pattern and locate the fault. At the end of paper, it has been shown that the proposed method has high accuracy, noise immunity, robustness against fault inception angles, and high impedance faults. [ABSTRACT FROM AUTHOR]

Active superconducting fault current limiter (ASFCL) is a new type of FCLs which can limit the fault current at different levels. It also has a particular ability to compensate for voltage series in the electrical power systems. In this paper, an optimal coordination method is proposed to calculate both optimal setting parameters of overcurrent relays (OCRs) and limiting the impedance of ASFCL. The optimal parameters of OCRs are obtained using the maximum pickup current and minimum trip time method. In the next step, by applying a new DG unit to the microgrid, the optimal limiting impedance of ASFCL is obtained so that all OCRs could be coordinated without changing the relay setting parameters. Using MATLAB software, a typical distribution system connected to a microgrid with ASFCL is simulated and the simulation results are evaluated in terms of the fault current limitation and OCRs coordination. Simulation results confirm the appropriate performance of the proposed ASFCL for the above-mentioned purposes. [ABSTRACT FROM AUTHOR]

• This paper presents a new method to discriminate internal fault from other cinditions. • Important features are extracted using the Clark's transform and modified hyperbolic S-transform. • The proposed method shows desirable performance in the events accompanied by current transformer. • The proposed method is not affected by the noise. In this paper, a new method is proposed for discriminating internal faults from other abnormal conditions in power transformers such as inrush currents, external faults, over-excitation, and ultra-saturation. Since the differential current signals are non-stationary, a powerful tool such as S-transform is needed for their time-frequency analysis. In this study, some important characteristics are extracted using the Clark's transform and modified hyperbolic S-transform according to which different conditions are distinguished and classified. These features include energy contour of first level, variance index, standard deviation of second harmonic component, and a special criterion. In this paper, all possible transient conditions and the effects of the saturation of current transformers are considered. Various simulations for different operating conditions of transformer are performed via PSCAD/EMTDC software. Also, the entire process of modified hyperbolic S-transform and the proposed algorithm are done in MATLAB software. Simulation results show that the proposed algorithm can be reliably used for the identification and classification of different faults in transformers. [ABSTRACT FROM AUTHOR]

The open-phase fault in vector-controlled drives is known as one of the most prevalent failures that require immediate detection. It is still challenging to develop a trustable fault diagnosis scheme at light load, transients, and low-speed regions. This paper presents a novel open-phase fault diagnosis strategy for three-phase induction motor drives over the entire speed range and for different load conditions. By taking advantage of the second-order rotational park transformation (SORP), new fault indices are proposed to identify the open-phase location without using any additional sensors or electric equipment. Comparing with root-mean-square (RMS) calculation-based methods, the proposed method detects the fault at least twice faster, with minimal system resources. The presented scheme may be implemented simply and is robust against the operating point changes. Proof of the proposed fault detection and localization method has been shown through experimental tests on a 250-W three-phase induction machine which is controlled by TI-DSP F28335. [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]

Ground fault in the rotor winding of generators can cause serious damage to the generators and consequently, to the power plant. This paper proposes a practical online technique to determine the ground fault location in the rotor winding of a synchronous generator. The proposed technique is based on the analysis of the measured voltage and input/output currents of the rotor winding. The main distinguishing feature of the proposed technique is that, contrary to the existing technique, it is applicable to various types of excitation system. The accuracy and applicability of the proposed technique is demonstrated through both computer simulations and experimental tests. The experimental tests have been carried out using a new device which works based on the proposed technique. The results show that the proposed technique can determine ground fault locations with a higher accuracy compared with the existing techniques. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]