Symmetrical Faults Research Articles

Preventing third zone maloperation during power system stressed conditions

Abstract The back-up third zone unit of distance relay may issue nuisance tripping command during different system critical events like power swing, voltage stress/instability and load encroachment. Since, such events are system symmetry phenomenon, the protection unit will not always able to discern them from three phase (symmetrical) fault in the distance relay third-zone region. The conventional relay algorithm fails to make a proper decision and results in unwanted tripping. This may further lead to system blackout. To mitigate this problem, a new approach based on the average rate of change of current (ARCC) is proposed. The method will work in integration with the conventional distance relay impedance setting algorithm to provide better results. The main advantage of the method is that it considers only local end current information. Within one power cycle, an accurate decision can be taken by the protective relay. The proposed method is validated considering IEEE 39-bus New England test system and the Indian regional power grid model modeled using EMTDC/PSCAD software. The simulation results for various critical cases and comparative analysis with existing methods shows effectiveness of the proposed method.

Numerical Study on Transient Behaviours of a 30-kW Generator Using a Coupling Method

As research and production technologies for high-temperature superconducting (HTS) materials have become increasingly mature, many high-efficiency and low-weight electrical machines made of HTS conductors have been successfully manufactured. In this paper, a transient numerical model for processing a three-phase symmetrical short circuit in a 30-kW HTS generator is proposed. It is based on an electromagnetic and thermal model, coupling the multiphysics of the rotating machinery and magnetic, circuit, and heat transfer modules. Some macroscopic characteristics of the generator, such as the output voltage and current waveforms, can be obtained. It also simulates the microscopic current shunting phenomenon between layers and temperature variation across HTS armature coils during a three-phase symmetrical short circuit fault. Then, some parameters of HTS conductors that are relevant to the temperature rise in coils are considered in this model. This simulation is an effective tool for analysing the transient performance of HTS generators in various fault operating conditions and could correspondingly provide an important guidance for the HTS machines’ preliminary design stage.

Machine Learning-Based Intrusion Detection for Achieving Cybersecurity in Smart Grids Using IEC 61850 GOOSE Messages

Increased connectivity is required to implement novel coordination and control schemes. IEC 61850-based communication solutions have become popular due to many reasons—object-oriented modeling capability, interoperable connectivity and strong communication protocols, to name a few. However, communication infrastructure is not well-equipped with cybersecurity mechanisms for secure operation. Unlike online banking systems that have been running such security systems for decades, smart grid cybersecurity is an emerging field. To achieve security at all levels, operational technology-based security is also needed. To address this need, this paper develops an intrusion detection system for smart grids utilizing IEC 61850’s Generic Object-Oriented Substation Event (GOOSE) messages. The system is developed with machine learning and is able to monitor the communication traffic of a given power system and distinguish normal events from abnormal ones, i.e., attacks. The designed system is implemented and tested with a realistic IEC 61850 GOOSE message dataset under symmetric and asymmetric fault conditions in the power system. The results show that the proposed system can successfully distinguish normal power system events from cyberattacks with high accuracy. This ensures that smart grids have intrusion detection in addition to cybersecurity features attached to exchanged messages.

Novel multilevel STATCOM for power system stability enhancement on DFIG-based wind farms

This work proposes the evaluation of the multilevel topology based on three-phase cells with a Single DC-link Cascaded H Bridge converter (SDC-CHB) with Model Predictive Control (MPC) as Static Synchronous Compensator (STATCOM) used to support DFIG wind farm operation. The well-known Hydro-Quebec system containing a 9 MW DFIG-based wind farm was chosen as a test bench to evaluate the proposed SDC-CHB steady and transient dynamic response to contribute to the DFIG fault ride-through. Simulation results demonstrate that the proposed topology enhances the power system stability and power quality, improving the voltage profile, on average, by 10% during symmetrical and asymmetrical faults. Furthermore, the SDC-CHB and MMC-CHB parametric study is presented proving the proposed topology robustness. Both topologies present similar steady and transient dynamic responses, corroborating that the proposed multilevel converter contributes to the DFIG fault ride-through with an enhanced topology when compared with classical multilevel converters.

A New Method for Dynamic Analysis of Multi-Machine Power Systems Including HVDC-links due to Symmetrical and Asymmetrical Faults

A New Method for Dynamic Analysis of Multi-Machine Power Systems Including HVDC-links due to Symmetrical and Asymmetrical Faults

An adaptive cumulative sum based method for unblocking distance relays in TCSC compensated transmission lines

Fault detection in transmission lines with thyristor controlled series compensators (TCSC) can be challenging, in particular during power swing conditions. A reliable unblocking method based on the adaptive cumulative Sum (ACUSUM) is presented in this paper. This method alleviates the limitations of conventional methods and has the capability to detect all asymmetric and symmetric faults with high accuracy and speed. The proposed method measures the negative sequence of the current signal for fault detection. Two simulation case studies consisted of the single machine and infinite bus (SMIB) and the IEEE standard 9-bus and three machine systems are simulated in PSCAD/EMTDC to evaluate the proposed method. It is shown that the non-linear behavior of TCSC will not impact the accurate performance of this method.

Calculation method of steady-state fault current for offshore wind farm

In order to improve the efficiency of solving the steady-state fault current of the offshore wind farm current collection system, In this method, the equivalent model of the PMSG and the VF control converter is established by taking into account the low-voltage ride-through in the case of failure. The Newton-Raphson method is used to iteratively calculate the fault equivalent network. By establishing a simulation model under PSCAD, the symmetric and asymmetrical faults in the collector system of a grid-connected permanent magnet wind turbine connected to the VSC-HVDC are simulated. Simulation results verify the effectiveness and accuracy of the calculation method.

A control strategy of converters based on constant extinction area for UHVDC system under hierarchical connection

The Ultra High Voltage Direct Current (UHVDC) systems under hierarchical connection, while improving the voltage support and current assimilative capacity of the receiving-end system, also bring new challenges to the security and stability of the power grid. An AC short-circuit fault at the receiving-end system can easily induce commutation failures (CFs) of the high-end and low-end converter at the same time, which seriously affects the stability of the system. Therefore, it is urgent to study the coordinated control strategy for the commutation failures of UHVDC systems under hierarchical connection. This paper analyzes the coupling mechanism and CFs characteristics of the high-end and low-end converters of a UHVDC system under hierarchical connection. Based on the commutation area theory of the three-phase full-wave bridge circuit, a coordinated control strategy is proposed to suppress CFs of the non-faulty layer converter of the UHVDC system under hierarchical connection. It can reserve enough extinction area for the non-faulty layer converter after an AC system failure occurs, thus preventing the occurrence of commutation failure. Finally, based on PSCAD/EMTDC, Zhundong-Wannan ±1100 kV UHVDC was built and the effectiveness of the proposed control strategy was simulated and verified. The simulation results show that the proposed control strategy can effectively suppress the simultaneous commutation failure of inverter station converters when symmetrical faults and asymmetrical faults of different levels occur in the receiving-end grid. This has important engineering significance for improving the stability of the DC transmission system.

Detection of islanding and non-islanding fault disturbances in microgrid using LMD and deep stacked RVFLN based auto-encoder

This paper presents a hybrid AC/DC microgrid consisting of multiple distributed energy sources, modeled in MATLAB/Simulink environment that undergoes islanding and non-islanding (symmetrical and unsymmetrical Faults) disturbances. These disturbances result in various changes in circuit parameters (voltage, current, and frequency) and this paper focuses only on disturbed current signals that are extracted from the solar and wind-connected buses. Further to extract rich and useful fault features from the extracted current signals, an adaptive detection technique, local mean decomposition (LMD) is proposed that results in series of product functions (PFs). Various feature extraction indices are used to extract the underlying features of the decomposed PFs that are processed through a deep-stacked random vector functional link network (RVFLN) based auto-encoder (AE) technique for classifying the faults. The effectiveness of the proposed RVFLN based AE technique is evidenced in terms of classification accuracy (CA) and confusion matrix (CM). The performance of the proposed technique has been evaluated through reliability analysis (MAPE, MAE, RMSE, and CM) by comparison with various artificial neural networks under both islanding and non-islanding mode of operation.

Fault Current Limiting Operations of Three-Phase Transformer Type SFCL Using Two Common Connection Points Between Secondary Windings

Three-phase transformer type superconducting fault current limiter (SFCL) using two common connection points between secondary windings, which consisted of three-phase transformer windings wound on three legs of E-I iron core and two/three superconducting modules (SCMs), were suggested and its fault current limiting operations according to ground-fault types were analyzed. To verify the effective operation of the three-phase transformer type SFCL using two common connection points between secondary windings, the unsymmetrical ground and the symmetrical ground faults were applied into three-phase power simulated system with the suggested SFCL. For the comparison, the ground faults were generated into three-phase transformer type SFCL with two/three SCMs. Through analysis on the test results, the SFCL with two SCMs was confirmed to have no different fault current limiting operation from the SFCL with three SCMs. The structure of E-I iron core with three magnetically coupled legs and the constitution of three secondary windings with two common connection points were analyzed to be contributed to the same fault current limiting operation. Furthermore, the power consumption and the joule energy of the SCMs comprising both the SFCL with two SCMs and the SFCL with three SCMs during the fault period had shown to be almost the same except for the transient period due to the quench time difference in case of the single-line ground fault.

Application of Thyristor Bridge-Type Non-Superconducting FCL with Buck Series Charging to Improve the FRT Capability of the DFIG System

Wind power generation is observing a significant use of doubly-fed induction generator (DFIG) due to its improved efficiency, but the converter used in the configuration is sensitive to the presence of a fault in the grid. This paper presents a fault ride-through (FRT) configuration, which includes a thyristor-based bridge-type non-superconducting fault current limiter (ThyBT-NSFCL) augmented with a buck converter. It has been observed that the proposed topology works fine under a temporary symmetrical fault. The analytical analysis has been carried out to observe the operating principle of the proposed ThyBT-NSFCL under both normal and fault conditions. A comparative study with other topologies such as switched impedance transformer-type non-superconducting fault current limiter (TT-NSFCL), series dynamic breaking resistor (SDBR), and without any current limiter (WCL) have been done to show the effectiveness of the proposed topology. The simulation results show that the proposed ThyBT-NSFCL is a better fault current limiter as compared with other limiters like TT-NSFCL, SDBR, and WCL. The simulation of the proposed ThyBT-NSFCL connected in series with a DFIG system is carried out using PSCAD/EMTDC software. The performance of the proposed topology is quite good, and it can be used as a reliable limiter for future wind energy applications.

Performance of Low Voltage Ride-Through Protection Techniques for DFIG Wind Generator.(Dept.E)

Due to the increase of the number of wind turbines connected directly to the electric utility grid, new regulator codes have been issued that require Low-Voltage Ride-Through capability (LVRT) for wind turbines so that they can remain online and support the electric grid during low voltage fault events instead of direct tripping of the wind turbines. This LVRT capability will increase the stability of the network and reduce the need for load shedding after the fault clearance. Each utility has its own grid codes for this LVRT. There are many types of wind generators, and currently the Doubly Fed Induction Generator (DFIG) is the most popular type among the leading wind turbine (WT) manufacturers. In this paper five LVRT methods for protection of DFIG during LV events are implemented and compared. The five methods are Crowbar, DC Chopper, series dynamic resistances, and two hybrid methods that combine DC chopp er with Crowbar and DC chopper with series dynamic resistances respectively. These methods were tested under different types of fault including symmetrical and unsymmetrical faults and their performances were compared.

Effective power transfer and reduced-order generalized integrator sequence based fault ride through strategy in grid connected DFIG based WECS

This paper deals with the control strategies of Doubly Fed Induction Generator (DFIG) based grid connected Wind Energy Conversion System (WECS) delivering power during normal and grid fault conditions. The system encompasses DFIG, Rotor Side Converter (RSC) and Grid Side Converter (GSC) connected back-to-back with a dc link, utility grid and local loads at point of common coupling. During normal system conditions, Tip Speed Ratio basedMaximum Power Point Tracking and Instantaneous Power Theory based reference current generation technique are employed for RSC, and GSC respectively to achieve maximum bidirectional power transfer and meeting the demand. Also, the power transfer operations during occasional conditions such as overloading and shorted stator winding are investigated. During grid fault conditions, a Reduced Order Generalized Integrator (ROGI) based Sequence Controller is employed to achieve stabilized real and reactive power injection to the grid by extracting the positive and negative sequence components of the grid voltages and currents. A supervisory control algorithm is developed for effecting a smooth transition of control schemes thereby avoiding system disturbances. The proposed control strategy is implemented in a simulation environment of a 10 MW grid connected DFIG based wind farm in MATLAB 2018b version. Various case studies are performed to validate the effectiveness of the proposed control strategies. The system is subjected to all possible grid faults including the most severe symmetrical fault and the controller is found to provide better grid support with appropriate real power transfer and reactive power injection. Also, the dynamic performance of the control strategy is experimentally investigated in the hardware setup of 1 kW grid connected DFIG based WECS. The system is operated under MPPT and FRT modes of operation under normal and grid fault conditions to prove the efficacious working of the proposed control strategies in DFIG based WECS.

Improved finite control set model predictive control for distributed energy resource in islanded microgrid with fault-tolerance capability

In this paper, improved finite control set model predictive voltage control (FCS-MPVC) is proposed for the distributed energy resource (DER) in AC islanded microgrid (MG). Typically, AC MGs have two or more power electronic-based DERs, which have the ability to maintain a constant voltage at the point of common coupling (PCC) as well as perform power sharing among the DERs. Though linear controllers can achieve above-mentioned tasks, they have several restrictions such as slow transient response, poor disturbance rejection capability etc. The proposed control approach uses mathematical model of power converter to anticipate the voltage response for possible switching states in every sampling period. The proposed dual-objective cost function is designed to regulate the output voltage as well as load current under fault condition. Two-step horizon prediction technique reduces the switching frequency and computational burden of the designed algorithm. Performance of the proposed control technique is demonstrated through MATLAB/Simulink simulations for single distributed generator (DG) and AC MG under linear and non-linear loading conditions. The investigated work presents an excellent steady state performance, low computational overhead, better transient performance and robustness against parametric variations in contrast to classical controllers. Total harmonic distortion (THD) for linear and non-linear load is 0.89% and 1.4% respectively as illustrated in simulation results. Additionally, the three-phase symmetrical fault current has been successfully limited to the acceptable range.

Sunflower optimization algorithm-based optimal PI control for enhancing the performance of an autonomous operation of a microgrid

This paper presents a novel application of the sunflower optimization (SFO) algorithm to enhance the performance of the inverter based microgrid. The vector cascaded control method is used to control the inverter which relies on the proportional-integral (PI) controller. The main goal is to select the parameters of the PI controller using the SFO algorithm. The multi-objective function for this research is deduced from the response surface methodology (RSM). The simulation results are tested under three different operating states which are: 1) the system conversion from grid-connected to stand-alone mode, 2) changing the load during stand-alone mode, and 3) symmetrical fault during stand-alone mode. The results verify the flexibility, justification, and applicability of the presented SFO algorithm versus the particle swarm optimization (PSO).

Certain investigations on fault analysis in a smart grid system using S-transform and their fault ride through using solid-state fault current limiter

This paper investigates certain fault analysis such as fault detection, identification and classification and their fault ride through (FRT) technique in a smart grid (SG) system using Stockwell transform (ST) and solid-state fault current limiter (SSFCL). ST when applied to symmetrical and asymmetrical faults for the detection and identification in a SG System yields a ST amplitude matrix (STA). The nature of the fault is identified through the features extracted from ST. STA with probabilistic neural network (PNN) classifier helps to detect the types of fault through the features extracted from fault signal. The outcome of PNN helps to classify the nature of fault like single-phase, two-phase and three-phase faults individually and with respect to ground fault in a SG system. Also, limiting the fault current ensures the continuous operation and reliability of SG under fault conditions. Further to avoid the disconnection of wind turbine system and solar PV system from the grid and overcome block out issue, SSFCL is employed. It improves the FRT capability of a SG system by controlling the fault current within the specified limit and retains the wind turbine system and solar PV system connected with the grid. The suggested scheme is modeled and the results are verified through the time domain simulation using MATLAB.

Finite-Time Consensus Tracking Neural Network FTC of Multi-Agent Systems.

The finite-time consensus fault-tolerant control (FTC) tracking problem is studied for the nonlinear multi-agent systems (MASs) in the nonstrict feedback form. The MASs are subject to unknown symmetric output dead zones, actuator bias and gain faults, and unknown control coefficients. According to the properties of the neural network (NN), the unstructured uncertainties problem is solved. The Nussbaum function is used to address the output dead zones and unknown control directions problems. By introducing an arbitrarily small positive number, the "singularity" problem caused by combining the finite-time control and backstepping design is solved. According to the backstepping design and Lyapunov stability theory, a finite-time adaptive NN FTC controller is obtained, which guarantees that the tracking error converges to a small neighborhood of zero in a finite time, and all signals in the closed-loop system are bounded. Finally, the effectiveness of the proposed method is illustrated via a physical example.

Enhanced Fault Ride-Through of Power Converters Using Hybrid Grid Synchronization

Inaccurate phase-angle jump (PAJ) estimation of the grid voltage during faults is one of the major causes for poor fault ride-through (FRT) performance of converters. To overcome this issue and make the converter’s current controller robust, this article proposes a hybrid grid synchronization transition technique. In this concept, a synchronous reference frame-based phase-locked loop (SRFPLL) grid synchronization method is used during normal grid operation and switched to an arctangent-based phase-angle estimation during grid faults. Simultaneously frequency estimation is switched to the arctangent derived frequency. A common transition method, which depends on the phase-angle error between the two-phase estimation techniques, is proposed to ensure a smooth transition between the hybrid phase-angle and frequencies. The transition technique is implemented using the current control of a three-phase voltage source converter in the SRF. The performance of the converter during both symmetrical and asymmetrical grid faults along with the FRT strategies is tested using real-time experiments. It is observed that the transition-based hybrid grid synchronization technique reduces the loss of synchronism duration. Additionally, it offers a more robust converter current control performance compared to the SRFPLL technique over a wide range of voltage sags and PAJs.

DC grids DC fault detection using asymmetric pole inductors

DC fault isolation is recognized as the major obstacle against widespread development of multi-terminal meshed DC grids. To fulfill DC grid protection requirements a fast, discriminative, and seamless DC fault detection and isolation mechanism is needed. This paper presents a DC grid protection system based on using asymmetrical pole inductors (APIs) for fault detection, and hybrid DC circuit breakers (HDCCBs) for fault isolation. The pole inductors are those normally used in series with cable-end HDCCBs to limit rate of fault current development. An intentional mismatch between positive and negative poles’ inductors is proposed for autonomous fault detection using the difference between positive and negative poles’ DC voltage magnitudes measured at all cable-ends. Better accuracy in discriminative symmetrical fault detection, and less sensitivity against fault impedance are achieved using lower series inductors compared to rate of change of voltage (ROCOV) technique as the most effective approach proposed so far. In order to investigate the proposed technique, a 2 GW symmetrical monopole DC grid equipped with proposed protection system is modeled in PSCAD. Simulation results are demonstrated to show the capabilities of the proposed protection system in fast and discriminative DC fault detection.

Application of the Automatic Segmented Hilbert Huang Transform Method for the Evaluation of the Single-Event Characteristics of Voltage Sags in Power Systems

Depending on the type of the electrical network, the source of the voltage sag (or dip), and the settings of the protective devices, the magnitude, duration, and phase of the voltage sag (or dip) during an event may behave differently. Because of the nonstationary characteristics of the voltage sag, the conventional fast Fourier transform (FFT) and Hilbert Huang transform (HHT) methods show ambiguities at the starting and at the recovery points of the voltage sag waveform. This can lead to errors in the calculation of the single-event characteristics (SEC) of the voltage sag. This article investigates the application of a novel automatic segmented HHT (SHHT) method for evaluating the SEC of the voltage sag caused by different types of symmetrical and unsymmetrical faults in both transmission and distribution networks. It also investigates the influence of several factors on the three important parameters of the voltage sag-the magnitude, the phase angle, and the point-on-wave (POW) of the voltage sag waveform. These factors include the types of fault, the location of the fault, and the X/R ratio of the lines before and after the fault, the transformer and load connections, and the POW of the sag initiation. The simulation results and tests with real data validate the effectiveness of the SHHT method in the evaluation of the SEC of the voltage sag when compared with those obtained using the traditional FFT and the analytical method.