Series-compensated Transmission Research Articles

The Analysis of Sub-Synchronous Resonance in a Wind Farm for a Doubly-Fed Induction Generator Using Modern Analytical Method

The occurrence of Sub-Synchronous Resonance (SSR) phenomena can be attributed to the interaction that takes place between wind turbine generators and series-compensated transmission lines. The Doubly-Fed Induction Generator (DFIG) is widely recognized as a prevalent generator form employed in wind energy conversion systems. The present paper commences with an extensive exposition on modal analysis techniques employed in a series of compensated wind farms featuring Doubly Fed Induction Generators (DFIGs). The system model encompasses various components, including the aerodynamics of a wind turbine, an induction generator characterized by a sixth-order model, a second-order two-mass shaft system, a series compensated transmission line described by a fourth-order model, controllers for the Rotor-Side Converter (RSC) and the Grid-Side Converter (GSC) represented by an eighth-order model, and a first-order DC-link model. The technique of eigenvalue-based SSR analysis is extensively utilized in various academic and research domains. The eigenvalue technique depends on the initial conditions of state variables to yield an accurate outcome. The non-iterative approach, previously employed for the computation of initial values of the state variables, has exhibited issues with convergence, lack of accuracy, and excessive computational time. The comparative study evaluates the time-domain simulation outcomes under different wind speeds and compensation levels, along side the eigenvalue analysis conducted using both the suggested and non-iterative methods. This comparative analysis is conducted to illustrate the proposed approach efficacy and precision. The results indicate that the eigenvalue analysis conducted using the proposed technique exhibits more accuracy, as it aligns with the findings of the simulations across all of the investigated instances. The process of validation is executed with the MATLAB program. Within the context of the investigation, it has been found that increasing compensation levels while simultaneously decreasing wind speed leads to system instability. Therefore, modifying the compensation level by the current wind speed is advisable.

Traveling wave-based fault locators: Performance analysis in series-compensated transmission lines

In this paper, the performances of one-ended and two-ended traveling wave (TW)-based fault location techniques in series compensated transmission lines (SCTLs) are thoroughly investigated, highlighting the impact of the series capacitors (SCs) and their associated overvoltage protection on such routines. To do so, a diversity of fault simulations were carried out on a realistic Alternative Transients Program (ATP) power system model of a 500 kV/60 Hz double-circuit SCTL located in the north region of Brazil. From the carried out studies, it is demonstrated that the two-ended algorithm is not impacted when the SCs are installed at the line ends, but the single-ended routines based on correlation functions are more affected by the SCs banks, even though some promising results may be obtained depending on their adjustments.

Comparison of Impact on Turbine Shafts Torsional Behavior for Integration of Two Types of Wind Farm into a Series-Compensated Transmission System

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.

Fast Detection of SSR for Wind Parks Connected to Series-Compensated Transmission Systems

The interactions between wind parks and the series-compensated transmission lines can bring about sub- or super-synchronous resonance (SSR) incidents which jeopardize the safe operation of the entire network. In practice, such incidents may emerge under various conditions as different types of wind turbines with various parameters can be deployed at several locations in the network. Hence, it is crucial to efficiently identify the conditions that lead to adverse interactions and their subsequent SSR incidents. This paper proposes a simulation-based method, namely disturb and scan (DaS), for fast and automated detection of SSR. The proposed technique uses small-scale disturbances in time-domain electromagnetic transient (EMT) simulations to perform spectral analysis along with positive-sequence impedance scans. Numerical results are presented and validated for benchmark systems that utilize type-III and type-IV wind turbines. The system operators can adopt the developed methodology to quickly assess the risks of SSR, evaluate conditions of instability, and improve their network protection and control schemes.

Study on the characteristics of secondary arc current of UHV high compensation degree TCSC line under the fine-tuning mode

Abstract In the transmission line, the series compensation device is often used to improve the transmission capacity. However, when the fixed series capacitor (FSC) is used in high compensation series compensation device, the stability margin cannot meet the requirements. Therefore, thyristor controlled series compensator (TCSC) is often installed in transmission lines to improve the transmission capacity of the line and the stability of the system. For cost considerations, the hybrid compensation mode of FSC and TCSC is often adopted. However, when a single-phase grounding fault occurs in a transmission line with increased series compensation degree, the unreasonable distribution of FSC and TCSC will lead to the excessive amplitude of secondary arc current, which is not conducive to rapid arc extinguishing. To solve this problem, this paper is based on 1000 kV Changzhi-Nanyang-Jingmen UHV series compensation transmission system, using PSCAD simulation program to established UHV series compensation simulation model, The variation law of secondary arc current and recovery voltage during operation in fine tuning mode after adding TCSC to UHV transmission line is analyzed, and the effect of increasing series compensation degree on secondary arc current and recovery voltage characteristics is studied. And analyze the secondary arc current and recovery voltage when using different FSC and TCSC series compensation degree schemes, and get the most reasonable series compensation configuration scheme. The results show that TCSC compensation is more beneficial to arc extinguishing under the same series compensation. Compared with several series compensation schemes, it is found that with the increase of the proportion of TCSC, the amplitude of secondary arc current and recovery voltage vary greatly. Considering various factors, the scheme that is more conducive to accelerating arc extinguishing is chosen.

Enhanced Compensation Filter to Mitigate Subsynchronous Oscillations in Series-Compensated DFIG-Based Wind Farms

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.

Evaluation of Phase Imbalance Compensation for Mitigating DFIG-Series Capacitor Interaction

The phase imbalance compensation concept is proposed in literature as an alternative way to mitigate classical subsynchronous resonance (SSR) problems in series-compensated transmission lines. However, a fundamental analysis to determine this concept’s ability to mitigate resonances between a doubly-fed induction generator (DFIG) and a series compensated transmission line, i.e., DFIG-SSR, is not reported in literature. Therefore, the objective of this paper is to investigate to which extent phase imbalance compensation is able to mitigate DFIG-SSR. For the phase imbalance compensation scheme, an analytical model that captures the relation between the level of series compensation, the degree of asymmetry between the compensated phases, and the resulting shift in resonance frequency is developed and validated using time domain simulations. Then, an optimisation framework is developed to search for an adequate level of compensation asymmetry, capable of mitigating the adverse interactions. The optimisation allows us to show that, even with the best set of parameters, phase imbalance compensation is not suitable for mitigating DFIG-SSR. The analytical model enables us to explain the underlying physical reasons for this and an attempt is made to explain why this concept is theoretically able to mitigate classical resonance issues. Lastly, directions for future research are identified.

Study and Solution of Current Differential Protection Disability for High Series Compensation Transmission Line

With the increasing day by day integration of large-size generators and tighter among the power systems, in internal fault, the fault current of Series Compensated (SC) lines could also be upturned. Therefore, the differential protection of SC transmission lines may stop working to operate because of less sensitivity. In this research article the causes for the current overturning in SC lines and its effects differential protection. The working characteristics of differential protection are analyzed by focusing on multiple-factors, for example, different series compensation degrees, types of fault, system operation mode, the difference of power angle, points of the fault, and transition resistance. An enhanced standard based on the current amplitudes and phases on both sides of the series compensated lines is proposed. Furthermore, to make stronger the operation characteristics of differential protection, the triple-fold line is chosen to get better sensitivity for internal faults in the article. The results are efficient to improve the protection sensitivity of SC lines during the internal fault. The PSCAD/EMTDC simulation and the power system dynamic physics simulation demonstrate that protection sensitivity is increased in the improved scheme. Keywords : Differential Protection, Series compensation, EHV/ UHV, Current reverse, sensitivity analysis. DOI: 10.7176/CTI/10-06 Publication date: August 31 st 2020

An improved setting method of the distance protective IEDs for series-compensated transmission lines based on a case study approach

An improved setting method of the conventional distance protective IEDs for the series compensated transmission lines based on the results of the comprehensive studies regarding the impact of a thyristor-controlled series capacitor (TCSC) is proposed in this paper. The proposed method considers the equivalent impedance of TCSC to calculate the distance protective IED setting values which can prevent the mal-operation. To verify and analyze the performance of the proposed method, the HILS(Hardware-In-the-Loop System) was constructed using RTDS and an IED. The IEC 61850-based dynamic characteristic tests were performed with this HILS.

Critical Review of Mitigation Solutions for SSO in Modern Transmission Grids

The replacement of conventional generation by power electronics-based generation changes the dynamic characteristics of the power system. This results in, among other things, the increased susceptibility to subsynchronous oscillations (SSO). First, this paper discusses three recently emerging SSO phenomena, which arise due to the interactions between (1) a doubly-fed induction generator and a series compensated transmission system; (2) a voltage source converter (VSC) and a weak grid; and (3) nearby VSCs. A fundamental review of these phenomena resulted in the requirement for a reclassification of the existing SSO phenomena. This reclassification is proposed in this work and is based on interacting components identified using participation factor analysis for the distinct phenomena. Second, a critical review of the existing mitigation measures is performed for these phenomena, highlighting the advantages and disadvantages of the solutions. The influence of the wind speed, grid strength, number of wind turbines, and several converter controller parameters are also discussed. To assist equipment manufacturers, control design engineers, and system operators in selecting and designing effective mitigation measures, the existing solutions are categorized in control solutions, hardware solutions, and solutions based on system level coordination. Finally, perspectives on open issues conclude this paper.

Influence of Series Compensation Degrees on Secondary Arc Current Characteristics under the Different Series Compensation Mode

AbstractThe high compensation degree series compensation has a broad development prospects in long distance and large-capacity UHV transmission lines. But it is generating secondary arc current contains low frequency components with high amplitude when the single-phase grounding fault occurs in the series compensated transmission line, which is not conducive to rapid arc extinguishing. To solve this problem, this paper based on the mechanism of generating secondary arc by series compensation transmission lines, and using ATP – EMTP electromagnetic transient program to establish the simulation model of UHV series compensation device. And the suppression effects of small resistance short connection fault series compensation and linkage bypass series compensation measures on secondary arc current and recovery voltage under different series compensation layout mode are studied respectively. The results show that the attenuation speed of the secondary arc current is related to the series compensation arrangement modes and the time when the series compensation device is short connected or bypassed. Series compensation device short connected or bypassed before circuit breaker tripping which can accelerate the arc extinction speed, and the suppression effect is better when the series compensated double platform segmentation layout is distributed on both sides of the line. The results can be used as a reference for the engineering design of UHV with large capacity and long distance and high compensation series compensation transmission lines.

An Effective Control Scheme for Multimodal SSR Suppression via VSC-Based Controller

Multimodal sub-synchronous resonance (SSR) induced by the interactions between the generator shafts and the fixed series capacitors has become a serious threat for the power system. To overcome this, a voltage source converter (VSC) based controller for multimodal SSR suppression, named sub-synchronous resonance dynamic suppressor (SSRDS), is presented and analyzed in this paper. The controller is placed at the point of common coupling (PCC) of the power plant for multi-generator SSR suppression purpose so that the investment costs can be minimized while making sure the requirements of the SSR damping. To quantify the contribution of SSRDS to the SSR damping, the damping torque analysis is carried out, which can reveal the influences of the operating conditions and the correlated control parameters on the damping performance. Furthermore, to avoid the negative affects between the different TMs in close range as well as maximize the damping ability of SSRDS, the parameters tuning method of the mode filters and the gain and phase shifters are proposed. A detailed nonlinear simulation model is established in PSCAD/EMTDC based on the Jinjie series compensated transmission system located in China. The damping torque analysis, the eigenvalues analysis and the simulation results have fully demonstrated the effectiveness and the robustness of the proposed SSRDS for multi-generator and multimodal SSR suppression under both small and large disturbances in various operating conditions.

Nonlinear SSR Damping Controller for DFIG Based Wind Generators Interfaced to Series Compensated Transmission Systems

This paper details a nonlinear Sliding Mode Control (SMC) based Sub-Synchronous Resonance (SSR) mitigation method for Doubly Fed Induction Generator (DFIG) based wind turbines interconnected to series compensated transmission systems. The proposed method is used to control the rotor side converter to mitigate SSR while ensuring decoupled torque and reactive power control ability of the DFIG is maintained. The proposed method is implemented on the detailed DFIG wind turbine model provided in the RTDS platform for validation via simulations. Results obtained indicate the controller is successful at damping SSR when tested under varying compensation levels and wind speeds.

FDOST-Based Fault Classification Scheme for Fixed Series Compensated Transmission System

This paper proposes a new method for diagnosis of fault type and faulty phase of a series compensated transmission line. The standard deviation (SD) principle together with the fast discrete orthonormal s-transform (FDOST) and the decision tree (DT) is applied for the purpose of fault classification. The FDOST, as an efficient signal processing tool, is used for extracting the features from a half cycle window of voltage and current signals sampled from one end of the power system network. Finally, the SD of a half cycle post-fault samples of the FDOST coefficients is calculated to form the input feature vector for the DT-based classifier. The features are processed by the DT to classify faults. The practicability of the proposed method is validated by modified Western System Coordinating Council 3-machine 9-bus system simulated in the PSCAD/EMTDC software and field fault data captured from a real transmission network of Chhattisgarh state, India. The results confirm that the proposed method reliably classifies all types of faults with high efficacy.

Analysis of Subsynchronous Resonance Characteristics and Influence Factors in a Series Compensated Transmission System

Series capacitor compensation is used to improve the utilization of existing power systems. Subsynchronous resonance (SSR) can be caused by series compensated lines, which would lead to turbogenerator shaft breakdown. A novel approach was presented in this paper to analyze the characteristics and influence factors of SSR in a series compensated transmission system. The system model of SSR, including the various modules of the electromechanical network, was established, and the eigenvalue results under 70% series compensation level were analyzed by eigenvalue analysis method for the the institute of electrical and electronics engineers (IEEE) first benchmark model (FBM). Compared with the results of the power systems computer-aided design (PSCAD) modeling and simulation, the effectiveness of eigenvalue analysis method was proven. After that, the eigenvalue analysis method was used to study, in detail, the effects of system series compensation levels, synchronous generator parameters, speed governing system parameters, and excitation system parameters on SSR characteristics. The research results show that the series compensation level has the greatest influence on the torsional mode damping of the system. The parameters of generator reactance, speed governing system, and excitation system have some effect on the torsional mode damping. The parameters of excitation system significantly affect the low-frequency oscillation damping.

Boundary protection for series‐compensated transmission lines

This study proposes a novel boundary protection for the series-compensated transmission lines, on the basis of the R - L differential-equation algorithm using the least square method and the theory of equal transfer process of transmission lines. This method takes the series capacitor (SC) as a boundary. The relative position of the fault with respect to the SC can be determined according to the fitting error of the least square method. This proposed protection method only uses one-terminal measurement, and the protection reach can be expanded to the total length of the series compensated line. The overreaching problem of the conventional distance relay in the series compensated transmission lines can be effectively overcome. A variety of PSCAD/EMTDC simulation tests show the validity of this new method.

Data-Driven Feature Analysis in Control Design for Series-Compensated Transmission Systems

One challenge in power-system control designs is the gap between numerical model-based analysis and complex real-world power systems. With increased data and measurements being collected from power systems, data-driven analysis (e.g., machine learning) may provide an alternative approach to reveal hidden information through learning from the real system data, and provide insights for better control scheme design during the utility planning process. In this study, data-driven feature analysis is performed to evaluate the relationships between series compensation, power generation, and path flows in a real transmission system, as well as temporal patterns. The main data-driven analysis methods, including statistical cross correlation, multinomial logistical regression, and classification and regression trees, are integrated for feature selection and developing predictive models of series compensation. Analysis results demonstrates the effectiveness of the proposed methodology in feature analysis and the potential to help improve power-system control scheme design.

SSR Analysis of DFIG-Based Wind Farm With VSM Control Strategy

The wind turbine is usually integrated into the power grid via back to back converter, and the inertia is decreased. Virtual synchronous machine (VSM) control was proposed to improve inertia of the wind farm. While for the doubly-fed induction generator (DFIG)–based wind farm with traditional control strategy, sub-synchronous resonance (SSR) has become a significant problem when it is connected to series compensation transmission lines. Therefore, the impacts of VSM control strategy for DFIG on SSR need to be investigated. In this paper, a detailed small-signal stability analysis model of the VSM control strategy is first established and eigenvalue analysis is then carried out. SSR in the wind farm with the VSM control under different series compensation levels, controller parameters and wind speeds is analyzed, and it is also compared to that in the wind farm with the conventional vector control strategy (VC). Simulations are performed in PSCAD/EMTDC to verify the result of SSR analysis.

Subsynchronous resonance assessment for a large system with multiple series compensated transmission circuits

Generators connecting to a series compensated transmission system can be exposed to subsynchronous resonance (SSR) and require a comprehensive vulnerability assessment. This study presents an SSR assessment framework and tools to more efficiently assess all types of generation in a large system with multiple generators and meshed series capacitors. The developed framework covers torsional interaction, torque amplification, and induction generator effect/control interaction and includes three assessment stages: topology screening, frequency scan, and detailed electromagnetic transient study. Topology screening based on max-flow min-cut theorem is applied to identify the set of transmission outages forming radial connections between generators and series capacitors. Frequency scan analysis is then conducted to further analyse the SSR vulnerability with all the possible combinations of transmission outages identified in the topology screening results. Nearby generators are modelled by frequency-dependent impedance tables, which consider the equivalent impedance looking into the generators over the range of 1-120 Hz. An electromagnetic transient simulation will be required to confirm the SSR vulnerability identified in the frequency scan analysis. The developed framework and tools have successfully been applied to a large power system with multiple series compensated circuits to ensure reliable generation interconnection and operation.

Investigation of subsynchronous control interaction in DFIG-based wind farms connected to a series compensated transmission line

The aim of this paper is to investigate the risk for subsynchronous control interaction (SSCI) in doubly-fed induction generator (DFIG) based wind farms connected to series-compensated transmission lines. For this purpose, a detailed analytical model of the frequency-dependent input admittance of the DFIG is derived. The developed admittance model is then used to get insights on the frequency characteristic of the DFIG wind turbine generator unit. In particular, the power-dissipation properties of the DFIG are used to identify those control parameters and operating condition that mainly impact the behaviour of the wind turbine in the subsynchronous frequency range. The admittance model of the wind farm together with the impedance model of the series-compensated transmission line are used to identify the risk for SSCI. Through the use of the Generalized Nyquist Criterion, it is shown that the closed-loop bandwidth of the current controller that regulates the rotor current has a major detrimental impact on the stability of the system. Furthermore, results show that the active power set-point and the level of series compensation also play an important role on the overall system’s stability. Time-domain simulations are conducted to validate the theoretical findings.