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This paper presents a new method for fault location in transmission lines with series compensation, using data from voltage and current measurements at both terminals, applied to artificial neural networks. To determine the fault location, we present the proposal of using current phasors, obtained from the oscillography recorded during the short circuit, as the input to the neural network for training. However, the method does not rely on the internal voltage values of the sources or their respective equivalent Thevenin impedances to generate training files for the neural network in a transient simulator. The source data are not known exactly at the time of the short circuit in the transmission line, leading to greater errors when neural networks are applied to real electrical systems of utility companies, which reduces the dependency on electrical network parameters. To present the new method, a conventional fault location algorithm based on neural networks is initially described, highlighting how the dependency on source parameters can hinder the application of the artificial neural network in real cases encountered in utility electrical systems. Subsequently, the new algorithm is described and applied to simulated and real fault cases. Low errors are obtained in both situations, demonstrating its effectiveness and practical applicability. It is noted that the neural networks used for real cases are trained using simulated faults but without any data from the terminal sources. Although we expect the findings of this paper to have relevance in transmission lines with series compensation, the new method can also be applied to conventional transmission lines, i.e., without series compensation, as evidenced by the results presented. [ABSTRACT FROM AUTHOR]

Protection of critical components in the power sector especially the transmission line system is very important to minimize loss of revenue, resources, and productivity. Improvement of power transfer capacity and voltage profile in smart the power grid is achieved by Series Compensation (SC). However, it poses many serious issues in the protection of compensated transmission lines. The majority of faults occurring in transmission lines are transient in nature for which service continuity can be regained by an auto-reclosing scheme. An efficient auto-reclosing scheme that can provide adaptive protection with reliable operation is required to prevent transient and permanent faults in the series compensated transmission line (SCTL). This work highlights the emulation of an Internet of Things (IoT) aided adaptive auto-reclosing scheme in association with an ESP32 controller that provides adaptive dead time control. The reclosing instance has been identified by means of a synchro-check relay. A real-time IoT-aided auto-reclosing scheme has been realized using the ESP32 controller that can generate a trip/reclosing signal instantaneously using the concepts of edge computing. The projected system has been also corroborated by simulating the modeled smart power grid network with wide variations in fault context in PSCAD. The validation of the set of rules is done in MATLAB software for the proposed auto-reclosing scheme. The extracted test outcomes of the simulation and its laboratory hardware implementation indicate an appreciable reduction in dead time which reflects the efficacy of the developed protection scheme. [ABSTRACT FROM AUTHOR]

This paper presents a magnetically controlled series compensation-fault current limiter (MCSC-FCL) which is composed of a magnetically controlled reactor (MCR) and a compensation capacitor. The device is improved from the traditional thyristor-controlled series compensation (TCSC), which has the characteristics of small output harmonics and simple control. The traditional saturated iron-core reactor is improved to increase the adjustable range of output reactance. During the fault, the MCR is connected to the grid alone to limit fault current; when the grid is normal, MCR and capacitor are used in series compensation mode. It effectively improves the utilization rate of the traditional current limiter MCR. In order to verify the effectiveness of the proposed MCSC-FCL, this paper analyzes the control characteristics of reactor models with different air gap structures by JMAG finite element analysis software, and verifies the voltage regulation characteristics and fault current limitation capabilities on MATLAB/Simulink platform. [ABSTRACT FROM AUTHOR]

Wind power has rapidly emerged as a leading renewable energy source, with doubly-fed induction generators gaining attention for their independent power control capability. Integrating doubly-fed induction generator-based wind farms into the grid requires significant upgrades to transmission and distribution infrastructure to fully harness wind energy's potential and address challenges like sub-synchronous control interaction. This phenomenon poses risks such as equipment damage and power supply interruptions. To mitigate these risks, a novel adaptive control strategy incorporating uncertainty and disturbance estimators, alongside H∞ and μ-synthesis controllers, is proposed. By introducing a time delay into the control system, oscillations can be detected and stabilized, ensuring system stability across various operational conditions. The controller parameters are optimized using a dynamic opposite learning-based enhanced mountain gazelle optimization algorithm. This algorithm is utilized to determine the optimal controller parameters that ensure system stability across different operational conditions. Simulation results conducted in MATLAB validate the effectiveness of the proposed controller in damping oscillations under different compensations and wind speeds. Specifically, it demonstrates superior damping capabilities at various wind speeds and compensations, enhancing power system stability and reliability. Results confirm the better damping capability of proposed controller under different compensations such as 75% and 45% and wind speeds such as 13 m/s, 7 m/s, and 11 m/s. This research provides better stability and reliability of power systems by dampening oscillations at 1.5 s, ensuring the sustainable integration of wind energy. [ABSTRACT FROM AUTHOR]

The induction generator effect (IGE) and the open-loop modal proximity (OLMP) are two different reasons why sub-synchronous oscillations (SSOs) in a series-compensated power system (SCPS) may occur. The IGE attributes the growing SSOs to negative resistance, while the OLMP explains the SSO mechanism from the standpoint of modal conditions. In this paper, we investigate the connections between the IGE and the OLMP through equivalent RLC circuit and open-loop modal analysis. Our investigation is conducted for two types of series-compensated power systems where either a synchronous generator or a DFIG is connected at the sending end. The investigation reveals the conditions, in which the IGE and the OLMP may jointly cause the growing SSOs, i.e., both the IGE and the OLMP can explain why the growing SSOs occur. Furthermore, the investigation indicates that the IGE and the OLMP may be totally irrelevant and lead to growing SSOs separately. This implies that it is possible that in a SCPS, the growing SSOs are only due to the IGE, and the OLMP is non-existent, and vice versa. Hence, when the growing SSOs occurs in a SCPS, examination based on both the IGE and the OLMP should be carefully conducted in order to find if the oscillatory instability is due to the IGE, or the OLMP, or both of them.

This paper presents a comparative study of various grid-forming control strategies under different series compensation levels to suggest the optimal control scheme for compensated lines. Series compensation is a technique used to insert a fixed capacitor in transmission line to maximize its power-transfer capacity and enhance the stability of the power system, however it may result in sub-synchronous oscillations issues. Virtual oscillator control and matching control schemes are recently proposed grid forming control strategies to ensure the power-sharing and synchronization capability of inverters under parallel operation. The mentioned schemes are designed for grid-forming control of inverter-based resources, with keeping traditionally used droop control as a benchmark for comparison. The IEEE first-benchmarked test model is modified by inserting series capacitance and energizing it with 1000MW grid forming inverter-based source in MATLAB/ Simulink. Distinct grid forming schemes, namely droop, matching, and dispatchable virtual oscillator control are implemented and critically analyzed for sub-synchronous oscillations under the same specifications as the test model. The simulation response of subsynchronous oscillations are investigated in time domain, frequency domain, and by calculating performance indices to verify the results in every aspect. The overall analysis justifies the damped, low transient overshoot and fast settling of sub-synchronous oscillations with the virtual oscillator control scheme at various compensation levels.

This paper presents an investigation into the performance of radial distribution systems (DS) with the installation of series capacitors in feeder sections. While the use of shunt capacitors to enhance voltage profile in DS has been acknowledged, the benefits of series capacitors have only been explored to a limited extent. Load flow analysis, while commonly used for offline evaluation of DS, can at times yield inconclusive results due to convergence issues. To mitigate this, an alternative approach is proposed using Artificial Neural Networks (ANN) to directly determine system performance. The viability of the proposed technique is evaluated for IEEE 12 and IEEE 33 bus DS's having series capacitor in feeder section for voltage improvement and line loss minimization. Therefore, this paper serves to contributes to the two main novelties namely, (1) Development of efficient ANN model to directly determine the maximum voltage regulation and line losses and (2) improvement of voltage and line losses reduction through series capacitor installation in feeder section of the DS. The results show that the utilization of an ANN model enhances accuracy and speeds up predictions, while the installation of series capacitors in feeder sections improves voltage regulation and reduces line losses. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the issue of the Sub-synchronous resonance (SSR) phenomenon in a series compensated DFIG-based wind power plant and its alleviation using a Battery Energy Storage-based Damping Controller (BESSDCL). A supplementary damping signal is developed considering the angular speed deviation and is incorporated into the BESS control system. Wide-area Measurement System data is used to determine the angular speed deviation. A linearized system model is developed to perform eigenvalue analysis, and to detect and examine unstable SSR modes. The variation of wind speed and three-phase fault are also taken into consideration to validate the robustness of the controller. To further verify the efficacy of the proposed damping controller, time-domain simulations are performed using MATLAB/Simulink. The application of the proposed BESSDCL stabilizes all the unstable system modes effectively at wind speeds of 7 m/s, 9 m/s, and 11 m/s, and at 40%, 50%, and 60% series compensation levels, as well three-phase fault conditions.

With the rapidly growing population, energy demand is increasing. The power supply to consumers must be free from distortions. By injecting voltage in quadrature with line current and varying the magnitude, the SSSC offers series compensation to the line. The injected voltage, which offers the effect of inserting an inductive or else capacitive reactance in series with the transmission line, is in quadrature with the line current. Using MATLAB/Simulink software, a phasor model of a 2-machine device with SSSC integration and POD as a subsidiary controller is simulated in this paper to evaluate efficient power flow regulation. The simulation has been used to study the time domain behavior of SSSC under normal and faulty conditions. The SSSC is implemented for correcting the voltage and analyzing power responses during a low voltage fault in the power system, whereas in normal conditions, the power system's voltage stability for maintaining steady acceptable voltages at every bus is analyzed. It has been revealed that POD controller assists SSSC by supplying the reference voltage signal to damp out the low frequency power oscillations. The objective of this study is to reduce the crest outreach and clearing time during the fault thus improving the transient stability. [ABSTRACT FROM AUTHOR]

Power system reliability refers to the ability of the system to satisfy the required power demand with sufficient generation and transmission. When a contingency occurs and in order to ensure the secure operation of the power system, load shedding might be needed to avoid the violation of the system security constraints. Adding series compensation will improve the ability of the system to meet the required demand by enhancing the transmission capacity, thus avoiding or reducing the dependence on load shedding. This leads to a reduction in the load curtailment during contingencies and an improvement of the overall reliability of the transmission system. However, the impact of the series compensation on the load curtailment depends on the parameters of the transmission network. The primary aim of this paper is to study the impact of adding series compensation on the power system reliability indices such as the Expected Energy Not Supplied (EENS) and the Expected Load Curtailment (ELC) by using the contingency enumeration method and the Monte Carlo Simulation (MCS). The reliability indices are evaluated on the IEEE 30-bus system using two different load shedding techniques in order to achieve the minimum load curtailments for each transmission line contingency. The impact of series compensation on system reliability is assessed during contingencies, where the placement and the settings of the series compensation device are determined to reduce ELC and EENS indices and improve the overall reliability of the transmission system. [ABSTRACT FROM AUTHOR]

Abstract As the load on distribution networks grows, system operators and planners are constantly challenged with the issue of voltage regulation or enhancing the quality of supply to customers at the load end of lengthy distribution lines. This paper presents the optimum determination of series capacitor units in a distribution system to maximize energy‐saving and enhance voltage levels. Interestingly, series capacitors can enhance the capability of transmission lines, reduce line losses, enhance the performance of buses with large induction motor loads and reduce voltage flicker. At the same time, the limitations of series compensation are taken into consideration while calculating its optimum values. To achieve the planning objective and optimal load flow objective, two strategies: The Improved Grey Wolf Optimization method (I‐GWO) and Tabu Search (TS), are hybridized to get the benefit of their advantages. The I‐GWO has a movement strategy called dimension learning‐based hunting for enhancing the balance between global and local search and maintaining diversity. The proposed (I‐GWO‐TS) algorithm can solve mixed‐integer programming to achieve the planning and the optimal load flow objectives. The proposed method can be applied to a real Egyptian distribution system that is heavily loaded, with poor voltage regulation, and also has high‐power losses. The obtained results demonstrate the capability of the proposed approach to determine optimal series capacitors’ location and sizing for maximization of energy saving. Further, the proposed method improves the network performance regarding the voltage profile and power losses, although the limitations of including series compensation were considered in the distribution system.

When ac and dc microgrids get exposed to load power changes or voltage transients, instability could occur owing to constant power loads’ (CPLs) behaviour. CPL has the negative impedance behaviour which is the reason behind such instability. A flexible alternating current transmission system (FACTS) devices are used in ac grid to help improve the power quality under such circumstances. Contrarily, dc networks doesn’t have such devices and suffers under similar situations. In this paper, the T-Type Modular Dc Circuit Breaker (T-Breaker) is proposed to act as a compensator device for dc networks when energy storage is integrated. Its compensation functions in addition to breaking and limiting a system’s current can be achieved using this single device. By implementing the T-Breaker’s shunt (current) and series (voltage) compensations, ride-through of grid transients can be achieved. T-Breaker’s series compensation function and how it can be integrated with the shunt compensation to improve the stability of a dc microgrid is the focus in this paper. In addition to modeling and simulating the system, both small signal and large signal stability are analyzed. Furthermore, a scaled down 270 V 5 kW system is utilized to validate T-Breake’s compensation functions and their influence on a microgrid’s stability.

Distance protection is popular in transmission networks and constitutes a large installed base across grid systems. The most widely accepted implementation of distance protection is based on voltage and current phasors. Today the electric grids are becoming increasingly complex and dynamic in nature. With power electronic converter interfaced systems such as renewables, HVDC, FACTS, etc., there is a need for fast, secure and reliable protection decisions. The phasor-based distance protection is prone to reliability issues in such networks and is inherently limited in speed. Recently, ultra-fast protection solutions based on fault induced traveling waves are commercially available. Although promising, such solutions may miss faults near voltage zero-crossing, falsely detects nonfaulty disturbances as faults and as such lack wider acceptance in contemporary transmission lines where protection security is a non-negotiable requirement. In comparison, time-domain based distance protection solutions have appeal in terms of reliability and speed. In addition, an ideal time-domain distance protection should be applicable to various networks such as series compensated lines, lines connected to renewables and long underground/sub-sea cables. In this paper, we propose a method for time-domain based distance protection to meet these requirements. The method operates based on current based operating quantity and a novel dynamic restraining quantity which is calculated for the fault zone boundary point. The proposed method inherently overcomes influence of series compensation, renewable integration and provides a fast and reliable identification of in-zone and out-of-zone faults. It is tested for various networks using laboratory experimental data and field records. Further it is implemented in an IED platform and tested with RTDS simulations in hardware-in-loop mode. The method is found to work satisfactorily and consistently over the extensive test scenarios.

This paper demonstrates the risk of a new control interaction phenomenon between a large-scale type-4 wind park (WP) and a 500 kV transmission grid in a super-synchronous frequency range. This study aims at (i) using the impedance-based stability assessment (IBSA) method to investigate this new interaction phenomenon, (ii) analyzing the impact of various transmission grid topologies, WP operating conditions, and wind turbine (WT) converter control parameters on the severity of the interaction. For ultimate accuracy, the frequency-dependent impedance characteristics of the WP are extracted using the electromagnetic transient (EMT)-type impedance scanning instead of a simplified analytical model. The performed analyses demonstrate that the WP generation capacity, length of the transmission lines, applied series and shunt compensation levels, presence of parallel lines, and grid side converter (GSC) control parameters of the WT can significantly affect the identified instability risk. The obtained results are validated through detailed EMT simulations. Although the type-4 WP is considered in this paper, the presented results can be generalized to any inverter-based resource (IBR) with a full-size converter (FSC), such as photovoltaic (PV) power stations.

During power supply swings, current and voltage waveforms are modulated with additional frequency elements which lead to maloperation of relays. This maloperation may cause cascade tripping of transmission lines, which results in the failure of electrical grid networks. Power Swing Blockers (PSBs) are employed to block and prevent maloperation of distance relays during power swing. Along with power swing, the presence of TCSC compensation in transmission line deteriorates the input signals to relays which make fault classification a complex task. During the PSB blocking period, modulated signals distorted with non-linearities of MOV operation complicate the fault diagnosis functioning. This challenge motivates to develop an algorithm for fault classification during power swings. To address aforementioned challenges, a Wigner Ville energy-based fault classification technique is proposed in this work. A modified 9 bus WSCC system with TCSC compensation is used for testing and validation of the proposed scheme. The scheme is tested for different cases like symmetrical, close-in fault, asymmetrical high resistance fault, and CT saturation, etc. The scheme is also validated against transient conditions like load and capacitor switching. The performance of proposed scheme is compared with existing schemes in literature. The above scheme is also implemented and validated on an Intel Cyclone V SOC FPGA. The results show that the proposed scheme classifies faults accurately during the simulation as well as on hardware platform. [ABSTRACT FROM AUTHOR]

This paper introduces a novel approach to fault localization in transmission lines with series compensation using nonlinear optimization. The objective function minimization provides information on the fault distance and the current at which the protective varistor starts conducting. Terminal source data, the maximum current capacity of the capacitor, and the operating curve of the metal oxide varistor protection element are not required. The proposed method successfully met the predefined objectives, with a maximum error of 1.13% in simulated scenarios. In validating the method using real cases from a Brazilian energy concessionaire, the errors were below 0.5%. [ABSTRACT FROM AUTHOR]

Series compensation is widely used to improve the electrical characteristics of long transmission lines and increase the power transfer capability. However, the insertion of a series capacitor introduces various phenomena that affect the performance of traditional distance relays. Moreover, the fault characteristics of renewable generation systems coupled with generation outputs that vary with weather patterns produce additional complications to the protection of transmission lines. This paper proposes the application of an enhanced sensitive power differential protection (SPDP) algorithm to the protection of series compensated transmission lines. The algorithm incorporates a criterion that improves the security of the protection by inhibiting the SPDP algorithm from operating for faults external to the protected line. Performance of the enhanced SPDP algorithm has been evaluated on a test system built in Digsilent Powerfactory software. Various in-zone and out-of-zone fault cases were simulated at different compensation levels and fault resistances. The results showed that the enhanced SPDP protection technique can detect in-zone faults along practically the entire transmission line (99.99 %) for compensation levels up to 90 %. The method operated reliably for faults with resistances up to 330 Ω.

This paper presents the issue of the Sub-synchronous resonance (SSR) phenomenon in a series compensated DFIG-based wind power plant and its alleviation using a Battery Energy Storage-based Damping Controller (BESSDCL). A supplementary damping signal is developed considering the angular speed deviation and is incorporated into the BESS control system. Wide-area Measurement System data is used to determine the angular speed deviation. A linearized system model is developed to perform eigenvalue analysis, and to detect and examine unstable SSR modes. The variation of wind speed and three-phase fault are also taken into consideration to validate the robustness of the controller. To further verify the efficacy of the proposed damping controller, time-domain simulations are performed using MATLAB/Simulink. The application of the proposed BESSDCL stabilizes all the unstable system modes effectively at wind speeds of 7 m/s, 9 m/s, and 11 m/s, and at 40%, 50%, and 60% series compensation levels, as well three-phase fault conditions. [ABSTRACT FROM AUTHOR]

This study presents a comparative analysis of fault detection and categorization methods in TCSC (Thyristor Controlled Series Capacitor)-compensated power systems. The analysis explores different techniques for extracting fault features from current data obtained from TCSC-compensated transmission lines. Machine learning algorithms, namely k-Nearest Neighbor (k-NN) and Support Vector Machine (SVM) are employed to categorize the extracted features, enabling fault detection and identification. To evaluate the efficacy of the proposed method, simulation tests were conducted on a test system, considering various fault scenarios. The simulations accounted for the presence of noise and TCSC correction, reflecting real-world operating conditions. The results demonstrate the efficiency of multiple approaches in accurately and swiftly detecting and classifying faults. By leveraging the capabilities of machine learning algorithms and extracting relevant features from current data, the proposed method offers a promising solution for fault detection and categorization in TCSC-compensated power systems. The ability to operate effectively even in the presence of noise and TCSC correction highlights the robustness and reliability of the proposed approach. [ABSTRACT FROM AUTHOR]

Protection engineers and academicians are continuously working towards better relaying for modern transmission structures. This has become a requirement because transmission structure, nowadays, is being updated with new technologies, e.g. flexible AC transmission system devices. In this paper, it has been observed that the differential DC plays an important role in distinguishing the internal and external faults. A criterion is then developed based on this unique feature of the differential DC for the identification of faults in modern transmission lines. The performance of the proposed criterion has been tested with the help of simulation study carried out using EMTDC/PSCAD software for a variety of fault types with variations in fault location, fault resistance, fault inception angle, and compensation level. Furthermore, the performance of the proposed algorithm is also investigated for several rare conditions such as evolving faults, cross-country faults, noise in measurement, and measurement error. The results prove that the scheme is selective, accurate, and robust for uncompensated and series-compensated lines while it is accurate for low resistance faults in the case of a shunt-compensated line. [ABSTRACT FROM AUTHOR]

In this research a new approach is introduced for detecting and classifying faults in a Thyristor-Controlled Series Capacitor (TCSC) compensated power system. Our proposed scheme utilizes both the Fast Walsh Hadamard Transform (FWHT) and machine learning algorithms. The FWHT is employed to extract fault features from current data obtained from the TCSC compensated transmission line, while machine learning algorithms such as K-Nearest Neighbor (K-NN) and Support Vector Machine (SVM) are used to classify the extracted features for the purpose of fault detection and identification. To evaluate the performance of our proposed scheme, simulation studies were conducted on a test system under various fault conditions. The simulation results demonstrate that our approach is highly effective in accurately and quickly detecting and classifying faults, even when noise and TCSC compensation are present. This scheme has the potential to enhance the reliability and efficiency of power transmission systems. [ABSTRACT FROM AUTHOR]

Series compensation is a cost-efficient way to enhance the system reliability and the power transfer capabilities of long transmission lines. As a result of series compensation, the sub-synchronous oscillation (SSO) causes a severe risk of torsional interactions (TI). Therefore, SSO becomes a serious risk factor in grid-integrated renewable energy systems. Numerous researchers have evaluated SSO instances in several types of asynchronous generators in power systems. In this paper, the categorization and the overview of the SSO phenomena have been vital for the different mechanisms, sophisticated systems, analytical techniques, and multiple reviews that have been propagated. This study provides SSO analysis for various types of renewable energy power plants. Finally, while dealing with conventional and new power systems, this study summarizes recent SSO-damping and alleviation techniques for practical perception and future perspectives. [ABSTRACT FROM AUTHOR]

Series compensations have been widely used in modern power systems to extend the power transfer capacity. Since more and more renewable power generation systems are installed in power systems, the grid-connected inverters (GCIs) used by the renewable power generations may interfere with series-compensated power lines, which introduce subsynchronous resonance (SSR) causing power system failure that has been observed in real cases. The phase-locked loop (PLL) of the GCI's control system is the main factor that can cause the SSR in the series-compensated power grid. To mitigate the impact of the PLL and obtain the stable operation of the power system, a q-axis voltage feedback method has been proposed in literature to damp the harmonic oscillations in the weak power grid where, however, the series compensation is not considered. Because the real q-axis voltage cannot be obtained, the q-axis voltage output from the PLL is used as the feedback variable in literature. However, due to the dynamic response of the PLL, the q-axis voltage output from the PLL is different from the real q-axis voltage, and the direct use of it for the damping of the SSR in the power grid with series compensations is invalid, which is investigated in this article. Besides, an observed q-axis voltage feedback method is proposed in this article to damp the SSR in the series-compensated power grid with GCIs being connected. By putting an observer in the q-axis voltage feedback path, the real q-axis voltage can be estimated and applied to damp the SSR. Simulation and experimental results have been provided to verify the effectiveness of the proposed observed q-axis voltage feedback method in the damping of the SSR. [ABSTRACT FROM AUTHOR]

Deep decarbonization is the goal of modern power systems, so it is inevitable that large-scale wind farms will be integrated into systems. This also gives rise to many problems, which have been studied in detail in the literature. However, these studies basically have two deficiencies. One is to assume that traditional generator units are fully loaded, and the other is not to compare the differences in the impact of different types of wind farm. This paper discusses these two points in detail. Taking a series-compensated transmission system as the research object, and assuming that the wind farm only replaces part of the power of the traditional generator unit in the transition period of energy conversion, the difference between the torsional vibration behaviors of the traditional unit caused by adopting different types of wind farm is discussed. The results of the study show that the impact of integration of the type 3 wind farm is dominated by the induction generator effect of doubly fed induction generator units. The penetration rate as low as 19% could cause instability. However, the paralleled metal-oxide varistor can effectively improve the stability. For the type 4 wind farm, the dominant factor turns out to be the de-rating operations of the steam turbine generator unit. The allowable penetration rate depends on the turbine damping. When the turbine damping is sufficient, the penetration rate can be as high as 87.5%. In conclusion, in order to integrate wind farms into a series compensated transmission system, one should not only focus on the compensation factor to avoid the sub-synchronous torsional vibrations, but also pay attention to the types of wind farm as well as the penetration rate. The findings can be used as the decision-making basis for the integration of wind farms during the energy transition period. [ABSTRACT FROM AUTHOR]

The introduction of series capacitors in transmission lines causes problems in terms of reliability and the security of distance protection relays. As distance protection is widely used in the transmission network, the challenge of applying it to series compensated lines has been taken up by utilities and relay manufacturers in various ways. In the field of power system protection, developments are largely driven by relay manufacturers, and are often not published in the academic literature; the status and trend of the relay manufacturer’s development are better found in their product manuals and patent activity. Further insight into specific implementations by transmission utilities can be found from publications in industry-led forums and some academic journals. This article surveys the status and development of distance protection for series compensated lines, with a focus on industrial implementation and practical considerations. Factors that influence the protection of series compensated lines are presented. Implementation examples reported by utilities are summarized as examples of the different situations encountered and the methods used to deal with them. It is observed that many utilities use communication-aided protection in series compensated lines, and distance protection is used with reduced reach. Solutions described in relay manuals are presented to demonstrate the manufacturers’ approaches to problems associated with series capacitor protection. While there are methods to counter voltage inversion, current inversion seems to represent a more serious challenge. A patent overview indicates the trends in this domain to be moving towards time-domain-based faster protection methods.

Series capacitors increase the power transfer limit of transmission lines. However, the protection of series compensated lines using only local measurement is challenging. Phasor based distance protection experiences delay and directional problems in the presence of a series capacitor. This paper presents an incremental quantity based distance protection algorithm for series compensated lines. The algorithm uses instantaneous voltage and current measurements from the local bus. It consists of capacitor voltage estimation, fault detection, phase selection, directional discrimination and distance estimation. The algorithm is extensively tested based on simulations with a line-end series capacitor, considering different source impedance ratios, fault inception angle, compensation levels, and fault resistance, location and type. This time-domain method is shown to work well, with fast decision time.

Power transfer to the load through transmission and distribution network is the major role of a power system operator. Transmission line congestion management is essential for satisfactory delivery of power to the customers. In this paper, a mathematical computational algorithm is developed using Genetic Algorithm (GA) based optimization which relieves congestion in the transmission lines. GA is able to remove congestion by proposing the appropriate change required in line reactance to relieve transmission line congestion. The proposed algorithm considers series capacitance compensation thereby increasing the line loading ability. The proposed method removes congestion automatically in any line, considering its line load limit and makes the grid smart through this self-healing property. This automated technique is able to propose the change in line reactance value required to remove congestion without changing the generation and load. To validate the effectiveness of the algorithm, it is tested in 5 bus IEEE, 14 bus IEEE, and 30 bus IEEE test systems. This algorithm is also verified in scaled down laboratory model of 5 bus IEEE system available in the laboratory. The testing results prove that the proposed GA based congestion management algorithm can relieve congestion in any line of any network automatically. [ABSTRACT FROM AUTHOR]

This article presents a new grid connected induction generator (IG) system having open-end stator windings with a series reactive power compensator. The proposed scheme consists of a two-level capacitor fed voltage source inverter (VSI) connected to one side of the stator windings of the IG while the other ends of the windings are directly connected to the grid. A current phasor oriented rotating reference frame based control scheme is developed to control the operation of the VSI to ensure that it compensates the reactive power required by the IG. Thus, the IG system can supply active power to the grid without drawing reactive power from it for excitation. Unlike the shunt compensated IG systems, the proposed scheme does not require an interfacing inductor for connecting to the grid thereby reducing the hardware footprint. The proposed scheme is validated by simulation using PLECS software and the simulation results are presented in the article. A prototype of the system was developed in the laboratory to experimentally verify the proposed scheme and the experimental results are also presented in this article. [ABSTRACT FROM AUTHOR]

Replacing conventional generation by power electronics based generation changes the dynamic characteristics of the power system. This results among others in the increased susceptibility to sub synchronous oscillations (SSO). This paper proposes a systematic procedure for mitigating the interactions between a DFIG and a series compensated transmission line using the phase imbalance compensation (PIC) concept. The impact of the series and parallel PIC on the resonance behaviour of the grid is first thoroughly investigated. Then, the influence of the system strength on the capabilities of the PIC to mitigate DFIG-SSR is assessed. Based on the findings a design framework which enables the systematic assessment of the series and parallel PIC for mitigating DFIG-SSR is developed and successfully implemented in the modified IEEE 39 bus system. Comparison between both concepts reveals that the parallel PIC is better suited to mitigate DFIG-SSR. The impedance based stability analysis and detailed time domain electromagnetic transient (EMT) simulations are used to respectively screen and validate the results. [ABSTRACT FROM AUTHOR]

This paper presents a control strategy to mitigate subsynchronous oscillations (SSOs) in doubly-fed induction generator (DFIG)-based wind farms integrated into series-compensated transmission systems. The strategy has two parts: in the first one, a compensation filter based on the motion-induction amplification concept is proposed to increase the damping of the DFIG machine in the subsynchronous frequency range; in the second one, a proportional-integral (PI)-like controller is designed using an optimal quadratic technique to minimize the control effort and the additional rotor voltage required by the SSO damping action. The SSO mitigation strategy acts locally on the DFIG control system reducing the negative resistance the rotating machine presents to the grid at subsynchronous frequencies; this approach reduces the control dependence on the topology and resonance frequencies of the network. The control strategy is validated with a case study based on the Argentinian power system and evaluated in a wide range of operating conditions, showing that the DFIG control system can be enhanced to mitigate poorly damped SSOs and increase the penetration level of wind power in the system. [ABSTRACT FROM AUTHOR]

Subsynchronous oscillation (SSO) has concerned scholars who work with doubly-fed induction generator (DFIG)-based wind farms which are interfaced with series compensated power systems. The critical factors impacting SSO are compensation level KC, proportional gain of rotor side controller (RSC) current tracking control KP3, number of DFIGs, and wind speed. In this paper, we analyze the stable domain of KC and KP3 as it is impacted by variable and uncontrollable wind speeds. Eigenvalues are used to conduct comprehensive stability analyses of the power systems, in which participation factors are employed to identify oscillation modes, and the trajectories of all the oscillation modes versus KC and KP3 are presented to support the identification results, time domain simulation based on Simulink is also applied to verify the conclusions. Monte Carlo simulation is conducted to simulate the variable characteristic of wind speed by sampling the Weibull distribution. The impacts of the number of DFIGs and transmission distance on the stable domain are analyzed, the stable and SSO probabilities are employed in the stable domain under a variable wind speed. The constant stable domain of KC and KP3 is presented, the power system will remain stable under a variable wind speed in this area.

The paper proposes mathematical models and algorithms to calculate processes and characteristics of induction motors in a series compensation of the reactive power. The developed algorithms are based on a mathematical model of the induction motor in phase coordinates. A complete system of differential equations of the electromechanical equilibrium of the stator and rotor circuits is used for a transient analysis. The algorithm to calculate the static characteristics is based on the projection method for solving the boundary value problem for a system of equations of the electrical equilibrium. [ABSTRACT FROM AUTHOR]

This paper introduces a fault detection and faulty phase selection technique for a double-circuit transmission line with thyristor-controlled series capacitor (TCSC). In a transmission system, the nonlinear operation of TCSC during switching modes distorted the voltage and current signals. The effect is more if the fault occurred at zero fault inception angle. An advanced protection approach to overcome these issues based on dynamic phasor estimation of current from local measurements is proposed in this work. The maximum transient component obtained from three phases is used as an index to accomplish the detection task. However, due to the nonlinear operation of different accessories connected to the controller unit such as metal oxide varistor (MOV) and thyristor circuit, identification of the exact faulty phase is still a challenge. To mitigate this issue, fuzzy decision-based rules are framed so that identification of exact faulty phases is possible. For validation, the method is tested on a 400-kV, 50-Hz power system model developed using EMTDC/PSCAD. Results obtained from simulation indicate that the method is reliable and a secure unit protection can be effectively provided to a double-circuit transmission system equipped with TCSC. [ABSTRACT FROM AUTHOR]

Summary: Integration of a series capacitor in a transmission line not only has advantages such as system stability and power factor improvements, voltage profile regulation, and power flow maximization but also shows some unwanted effects such as current and voltage inversion, change in line impedance, and subharmonic frequency that leads to mal‐operation of the conventional protection scheme. This paper introduces a fault detection method for a series‐compensated line. An algorithm is proposed that uses the extracted DC component of currents at both sending and receiving ends to detect the fault and generate a trip signal. The proposed protection criterion is successfully examined for diversified (adverse) conditions using PSCAD/EMTDC simulations. [ABSTRACT FROM AUTHOR]

Summary: Objectives: This paper explores the performance of the Single Machine Infinite Bus (SMIB) power system integrating a Photovoltaic (PV) generator when compensated by the Thyristor Controlled Series Capacitor (TCSC) and the Static Synchronous Series Compensation (SSSC) Flexible Alternating Current Transmission System (FACTS) devices. Method: The analysis is performed after the introduction of a step change in the mechanical input and excitation voltage of the synchronous generator connected in parallel with the PV generator at different levels of solar intensity. Time domain simulations based on a non‐linear dynamic mathematical model are used for numerical simulations. Results: The simulation results demonstrated the effectiveness of the addition of TCSC and SSSC FACTS devices to improve the power transfer capacity of the SMIB power system with a PV generator. Conclusion: The response of TCSC and SSSC is almost similar. Nevertheless, the introduction of the two FACTS devices does not achieve a system stable operation at 50% of the total level of solar irradiance. TCSC is more effective than SSSC in maintaining the stability of the system. [ABSTRACT FROM AUTHOR]

Summary: This paper demonstrates the functionality and control of the gate‐controlled series capacitor (GCSC), a new FACTS device composing a pair of antiparallel GTOs in parallel with a fixed capacitor, to mitigate subsynchronous resonance (SSR) in a thermal generation plant connected to a series compensated transmission line. Firstly, by the use of both small‐signal stability analysis and time‐domain simulation, it is revealed that the studied system compensated by the series fixed capacitor is potentially unstable due to the first torsional mode. Then, in order to take benefits of series compensation without the risk of SSR, the fixed capacitor is replaced by GCSC. The capability and effectiveness of the GCSC to damp SSR are validated using modal analysis and time‐domain simulation. Furthermore, GCSC is used in conjunction with a fixed series capacitor to minimize the overall cost of compensation. For this purpose, unlike previous studies, a linear controller is used to stabilize the system. In this study, the IEEE First Benchmark Model is considered as a case study, and MATLAB/Simulink is used as a tool for modeling and design of the control system. Also, time‐domain simulations are done using PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

To charge the battery of electric vehicles (EVs), inductive power transfer (IPT) system has been considered to be more appropriate than traditional plug‐in system especially for its security and convenience. This study proposes a hybrid IPT system for EVs charging applications adopting one transmitter coil with series compensation and two receiver coils with series compensation and LCL compensation. With the help of the two receiver coils and proper parameters design, the proposed system can naturally obtain constant current (CC) and constant voltage (CV) outputs and the maximum output power can be naturally limited which can prevent the system from possible overload. Therefore, the reliability of the proposed system is increased. Since the mode switching process can be automatically realised according to the value of battery equivalent load without extra control strategy and circuit, the fixed‐frequency control can be used. Therefore, not only zero phase angle condition, but also the soft switching can be achieved. The theoretical analysis is presented with the design process of the IPT coils and resonance parameters for required battery charging profile. The performance of the system is verified by a 3.3 kW experimental prototype. The experimental results coincide well with the theoretical analysis. [ABSTRACT FROM AUTHOR]

It has become a great challenge to mitigate the unstable subsynchronous control interaction (SSCI) in practical series compensated wind power systems, mainly because of the system-wide influential factors, such as the constantly changing wind speed, number of in-service wind turbines, and operating conditions. In an effort to address the challenge, this paper proposes a simple yet practical grid-side subsynchronous damping controller (GSDC), which consists of a subsynchronous damping controller (SDC) supplemented to a subsynchronous current generator (SCG). The GSDC utilizes bus voltages and line currents as feedback signals and injects currents at the subsynchronous frequency into the system to provide active damping. The parameters of the SDC and SCG can be optimized for any system facing SSCI issues. In this paper, a GSDC is developed and optimized over an EMT model of a realistic system. The proposed scheme has demonstrated its effectiveness and robustness through controller-hardware-in-the-loop tests for mitigating SSCI over a wide range of operating conditions. This paper has paved the way for the commissioning of a practical GSDC in a real-world system that has experienced unstable SSCI incidents. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive solution to mitigate the sub-synchronous oscillation (SSO) in wind farms connected to series-compensated transmission lines. The concept of motion-induction amplification (MIA) is introduced to reinterpret the physical root cause of the negative resistance in doubly-fed induction generators (DFIGs). Based on this new interpretation, a novel control scheme called motion-induction compensation (MIC) is proposed to counteract the MIA effect. The MIC control eliminates the negative resistance in DFIGs across the entire frequency range, and makes the Type-III (DFIG) generator behave like a Type-IV generator in dynamics. The proposed solution provides wide-range SSO damping and also shows excellent robustness against model and measurement errors. [ABSTRACT FROM AUTHOR]

The protection of mutually coupled series capacitor-compensated (SCC) parallel transmission lines is a more complicated task than uncompensated lines due to the effect of mutual coupling, inter-circuit faults, and non-linearity of effective impedance of SCC line. A method that can overcome these issues and still work efficiently is a supervised learning-based method which is an adaptive technique. Hence, in this work, various supervised learning-based intelligent schemes like artificial neural network (ANN), support vector machines (SVM), and decision tree (DT) are employed to find a suitable method for the protection of series capacitor-compensated lines. Discrete wavelet transform has been used to process the three-phase current signals of the parallel lines measured at one terminal only. A moving window of 20 samples is selected, and approximate wavelet coefficient is calculated up to level 1 using DB-4 mother wavelet. The resultant is then given as input to the intelligent schemes (ANN, SVM, and DT). The proposed intelligent schemes have been tested with variety of fault conditions such as inter-circuit faults, cross-country faults, transforming faults, single-circuit operation, and high resistance faults. A large number of fault simulation studies corroborate that DT-based fault classification method is better than ANN and SVM. The accuracy of faulty phase and ground identification scheme is 100% for all the tested fault cases. Hence, the proposed supervised learning-based intelligent method can be implemented in real power system network effectively. [ABSTRACT FROM AUTHOR]

To avoid the under/over-reaching problems of distance protection of extra high voltage/ultra high voltage transmission lines (TLs) in the presence of series compensation, pilot relaying scheme can be preferred. In this article, a pilot relaying scheme is proposed which is unaffected by source-to-line impedance ratio variations and is based on the estimated phase error (EPE) of shunt charging component of the TL. For external fault, EPE is very small or close to pre-fault EPE while for internal fault, EPE is more than 10 times of pre-fault EPE. This scheme can be used to protect the series-compensated line as well as an uncompensated line with the same threshold value. The prerequisites for this scheme are the parameters of the TL which is to be protected. The scheme has been tested using power system computer aided design/electromagnetic transient and DC simulations for three different types of test power systems. The proposal is found to be accurate for different test systems, fault types, variations in compensation level, source impedance, fault location and fault resistance. [ABSTRACT FROM AUTHOR]

This study introduces a fault location technique for three-terminal series-compensated untransposed parallel transmission lines utilizing the three terminals' synchronized data. The proposed technique is applicable for short or long lines as distributed parameter line model is employed and the potential couplings are considered. The fault location for both uncompensated line sections is obtained adopting previously introduced fault location technique. The faulty phases are required initially to be recognized for series-compensated transmission line. The adopted fault location technique for series-compensated line section is derived based on the resistive nature of the fault impedance. The obtained fault locations for each line section are compared with each other to distinguish the faulty branch and obtain the fault location. DIgSILENT Power Factory and MATLAB programs are utilized for simulation studies and required calculations. The obtained results prove the efficacy of the introduced technique. [ABSTRACT FROM AUTHOR]

The paper presents a novel approach for classification of faults in Extra High Voltage (EHV) transmission line with series compensation. The proposed algorithm utilizes single end currents extracted from three phases of a transmission line given to a fault detection and classification system. A detailed model is constructed to analyze fault patterns occurring on a dual feed system with multiple series compensation provided on EHV transmission line. The algorithm uses a full cycle of post-fault currents. A Multiresolution Analysis Wavelet-based decomposition technique is used to provide a joint time frequency analysis. Extensive study is done by designing different fault classifiers using Support Vector Machine (SVM) with different feature vector groups. The SVMs with different parameters are compared to show performance of SVMs in given feature space of faults. A new algorithm is proposed with Ensemble method having group of different classifiers, namely, Artificial Neural Network (ANN), K-Nearest Neighborhood (KNN) and SVM. A combination of feature selection with Ensemble Classifiers is trained and tested on a wide range of fault patterns. A significant improvement in performance is obtained with different combination of features in Ensemble Classifier using subspace partition method.The proposed Ensemble Classifier provides an accuracy of 99.5%. [ABSTRACT FROM AUTHOR]

When wind farms, which is based on double fed induction generator (DFIG), are connected to the series compensation power system, the phenomenon of sub-synchronous oscillation (SSO) may occur. In order to study the sub-synchronous oscillation in wind power connected to series compensated power system and its influencing factors, we used RT-LAB to establish a simulation model concerning wind power connected to series-compensation power system. This model take a wind power connected to series compensation power system in north China as prototype. All influence factors of wind power SSO are simulated and analyzed by using time domain analysis method. The simulation results show that the effects of wind speed, series compensation degree and proportional control coefficient of rotor side converter (RSC) are most obvious.