Three-phase Short-circuit Fault Research Articles

A Fault Direction Criterion Based on Post-Fault Positive-Sequence Information for Inverter Interfaced Distributed Generators Multi-Point Grid-Connected System

In response to the poor reliability in identifying fault direction in distribution networks with Inverter Interfaced Distributed Generators (IIDGs), considering the control strategy of low-voltage ride-through, a fault direction criterion based on post-fault positive-sequence steady-state components is proposed. Firstly, the output steady-state characteristics of IIDGs considering the low-voltage ride-through capability are analyzed during grid failure, and the applicability of existing directional elements in a distribution network with IIDGs connected dispersively is demonstrated. Subsequently, for the typical structure of an active distribution grid operating under flexible modes, the positive-sequence voltage and current are examined in various fault scenarios, and a reliable direction criterion is suggested based on the difference in post-fault positive-sequence impedance angles on different sides of the lines that are suitable whether on the grid side or the IIDG side. Lastly, the reliability of the proposed direction criterion is verified by simulation and the results indicate that the fault direction can be correctly determined, whereas phase-to-phase and three-phase short circuit faults occur in different scenarios, independent of the penetration and grid-connected positions of IIDGs, fault location, and transition resistance. It is suitable for fault direction discrimination of an IIDGs multi-point grid-connected system under a flexible operation mode.

Fault probability identification method for distribution networks based on mov-MF distribution

To address the fault identification challenge in distribution networks, a method leveraging a mixture of the von Mises–Fisher (mov-MF) distribution model for fault probability identification is proposed. Initially, the synchronous phasor measuring unit is employed to gather the post-fault steady-state voltage phase quantities, and then, the voltage phase angle values are combined to form a three-dimensional feature quantity. Subsequently, the mov-MF distribution model is initialized through the spherical K-means algorithm and the minimum message length algorithm. This model is further refined via the expectation–maximization algorithm to iteratively optimize distribution parameters. The test set data are input into the mov-MF distribution model, which has been constructed using typical fault data, to discern fault types. Finally, the efficacy of the proposed method is validated through simulation verification conducted on the IEEE 33-node distribution system. The analysis of the examples demonstrates the accuracy of the mov-MF distribution model-based fault identification method in identifying single-phase ground, two-phase ground, two-phase interphase, and three-phase short-circuit faults.

Simulation and analysis of short circuit fault in ship power system based on simulink

Abstract In this paper, a short-circuit fault simulation of a ship’s electrical power system is carried out based on Simulink. According to the power system sketch of the ship, a simulation model is built, initial conditions are set, two-phase short-circuit faults and three-phase short-circuit faults are simulated, and the simulation results are analyzed. The results show that the short-circuit fault has a large impact on both the generator side and the load side, in which the impact on the load side is more serious. At the generator side, the voltage of the corresponding phase drops by about 1/3-1/2, and the current increases by about 1.5 times. At the load side, when a two-phase short circuit occurs, the voltage drops to half of the original one, and when a three-phase short circuit occurs, the voltage drops to 0. The short-circuit current has the largest value at the beginning of the short circuit, then oscillates and decays, and finally stabilizes at about 15 times the normal working current.

Research on Low Voltage Ride-through Characteristics of 300 MW VSPSH Based on BPA

Abstract With the development of new energy, the power grid scale is constantly expanding, which also brings new challenges to the stability of the grid. When some faults occur in the power grid, it leads to a voltage dip; if most of the devices are removed from the power system, it is easy to cause problems of stability and losses. Therefore, it is necessary to investigate the low voltage ride-through (LVRT) characteristics of power electronic equipment with large capacity before grid connection. Different from constant-speed pumped-storage hydropower plants (CSPSH), variable-speed pumped-storage hydropower (VSPSH) units have broad prospects for development in China due to their characteristics of frequency and voltage regulation, energy saving, and high efficiency. In this paper, the three-machine-nine-node model of 300 MW VSPSH is built based on BPA, and the large voltage dip caused by a three-phase short-circuit fault at the grid side is designed to test the LVRT capability of 300 MW doubly fed VSPSH.

An improved design for virtual synchronous generator control loop based on synergy theory

Virtual synchronous generator (VSG) technology has achieved some results in distributed generation networks and enhanced system stability. For problems that may occur in the system due to ignoring parameter linkages, this paper designs a synergistic controller that establishes the connection between the active frequency and the reactive voltage control loop based on synergy theory. As the output of the synergetic controller, the derived control law u is added to the power frequency control in the form of negative feedback. Two disturbance forms, a step disturbance, and a three-phase short-circuit fault, are set up. The conventional droop control and synergetic droop control results are compared using a MATLAB simulation system. Then, the system parameter variations were studied and analyzed, and the sensitivity of the control system with different values of parameters K1, K2, and K3 in the case of a three-phase short circuit was analyzed, which provides a reference guide for selecting parameters in later control optimization. Finally, the control effectiveness of a multi-machine VSG system was tested. The simulation results show that the proposed method has a pronounced effect on making the system stabilize quickly, which illustrates the effectiveness of this technique.

Distribution network adaptive protection system based on artificial intelligence

Abstract With the continuous development of society, the requirements of enterprises and the public for the reliability of the power system are also improving, and the fault identification and protection action of the distribution network is conducive to the comprehensive analysis and overhaul of the line, which is of great significance. In this paper, a short-circuit fault identification method for distribution networks based on artificial intelligence technology is proposed to categorize and predict power system faults using an association rule algorithm. Then, a distribution network adaptive protection strategy based on the equivalent impedance of the distributed energy system is proposed, which real-time adjusts the setting value and criterion of the protection through the distribution network containing distributed energy devices connected to the grid and adjusts the working status in normal operation, realizing that the current protection of the distribution network adapts itself to the change of the working conditions of the distribution network system of IIDG. Simulation results show that when two-phase grounding and three-phase short-circuit faults occur in the distribution network under the protection of the adaptive system. The protection circuits start instantaneously in 0.005s, which realizes the functions of the fast startup, self-sustained operation, and controllable shutdown when faults occur in the distribution network. Meanwhile, the feasibility of the scheme is verified by utilizing the system to output short-circuit faults in the case of IIDG grid-connected or off-grid when the respective integrating values are greater than the positive sequence short-circuit current values.

Pilot Protection of a Distribution Network with Distributed Generators Based on 5G and Dynamic Time Warping Considering Cosine Transform

The application of 5G-based communication for pilot protection in a distribution network with distributed generators is becoming increasingly widespread, but the existence of a 5G communication transmission data delay adversely affects the rapidity and reliability of the pilot protection based on the principle of the traditional dynamic time warping distance (DTW) algorithm. Therefore, to address this problem, and according to the difference in fault currents between distributed generators and synchronous machines, a new scheme of pilot protection based on the principle of an improved DTW is proposed. The scheme firstly performs cosine transform on the fault current sequence, and then it normalizes the DTW value. Finally, the proposed scheme is verified via simulation. The simulation results show that, compared with the traditional DTW, the proposed algorithm has better anti-delay characteristics and a stronger anti-interference ability, and the scheme can quickly and reliably identify in-zone and out-of-area faults with strong noise resistance. Further, the action times for a single-phase ground fault, two-phase ground fault, two-phase-to-phase fault, and three-phase short-circuit fault were reduced by 2.9 ms, 4.54 ms, 5.81 ms, and 5.89 ms, respectively. In addition, it is also sui for a distribution network with a high wind and photovoltaic penetration rate.

Enhancing the Dynamic Stability of Integrated Offshore Wind Farms and Photovoltaic Farms Using STATCOM with Intelligent Damping Controllers

To build a large-scale renewable energy integrated system in the power system, power fluctuation mitigation and damping measures must be implemented during grid connection. PID damping controllers and traditional intelligent controllers with pole configuration are usually used for improving damping. Integration of large wind power plants and photovoltaic power plants into the power system faces transient power oscillation and fault ride-through (FRT) capability under fault conditions. Therefore, this paper proposes a static synchronous compensator (STATCOM) damper based on a recurrent Petri fuzzy probabilistic neural network (RPFPNN) to improve the transient stability of the power system when large offshore wind farms and photovoltaic power plants are integrated into the power system, suppress power fluctuation, and increase FRT capability. To verify the effectiveness of the proposed control scheme, a three-phase short circuit fault at the connected busbar is modeled in the time domain as part of a nonlinear model. From the comparison of simulation results, the proposed control scheme can effectively slow down the transient fluctuation of power supply to the grid-connected point when the grid is faulty, reach steady-state stability within 1–1.5 s, and reduce overshoot by more than 50%. It can also provide system voltage support at an 80% voltage drop and assist in stabilizing the system voltage to increase FRT capability. It also improves stability more than PID controllers when disturbances are present. Therefore, it maximizes the stability and safety of the power grid system.

A novel non-iterative based framework for quick dynamic assessment of wind energy dominated multi-machine power system

Renewable Energy Sources have considerably expanded in recent years to address the widening energy deficit in modern power systems. Integrating these sources raises significant concerns for power system management, with transient stability constraints of networks being one of the growing issues for engineers and researchers. In this paper, the impact of Doubly Fed Induction Generators integration is analyzed to examine the transient stability on two test models. A Coupling Strength Index formulated from Network Structural Characteristics Theory is explored to detect the weakest transmission line. This method identifies line 7 to 8 and 5 to 6 as the weakest line with coupling strength index of 0.02739 and 0.105158 for IEEE 9 and 39 bus system, respectively. The system’s transient stability is then investigated with and without the Doubly Fed Induction Generators, considering a three-phase short-circuit fault applied at the middle of the identified line. Several characteristics associated with the system such as generator speed, rotor angle, and electric power were investigated. The simulation was carried out using DIgSILENT Power Factory and the results indicate that the systems are negatively impacted by the integration of Doubly Fed Induction Generators.

Recommendations on Selecting the NPP Generator Transformer VA Rating

The specific features of selecting the VA rating of a nuclear power unit step-up transformer are analyzed. The analysis is based on the provisions of the international standard IEEE C57.116-2022, which is a guide for transformers connected to turbine generators, taking into account the definition of the term “transformer VA rating” according to Russian and European standards (GOST 16110-82 and GOST 30830-2002). The definition of this term in this guide differs from that adopted in Russia and the EU member states. An example of analytical calculation of the generator step-up transformer steady-state apparent power in the reactive power generation and absorption modes (turbine generator inductive and capacitive operation modes) is considered. The calculation is confirmed by the simulation results in the ETAR software package. The inexpediency of selecting the generator step-up transformer VA rating from the standardized range of rated capacities according to GOST 17544-85 and GOST 9680-77 is substantiated. An adverse effect of overestimating the transformer VA rating on the maximum three-phase short-circuit fault current in the generator voltage circuit (in the main electrical connection circuit section between the turbine generator and step-up transformer) of a nuclear power plant unit is shown.

Dynamic State Estimation of Synchronous Machines Using Iterated Square-Root Cubature Kalman Filter and Synchrophasor Measurements

Power system dynamic state estimation is the first prerequisite for control and stability prediction under transient conditions. For a stable and reliable power system, it is crucial and helpful to have accurate, precise, and up-to-date information on the states of the synchronous machines- rotor angle and rotor speed deviation. This paper proposes an application of the Iterated Square-root Cubature Kalman filter (ISCKF) to estimate these main states of synchronous generators. The ISCKF method consists of two step modification - one is the square-root step modification of CKF and the next step is the addition of iterative approach to the square-root CKF method. To demonstrate the performance of the proposed approach during a three-phase short circuit fault, the simulation results, are compared with that of Extended Kalman Filter (EKF), Unscented Kalman Filter (UKF) and Cubature Kalman Filter (CKF). The test systems considered are a single machine infinite bus (SMIB) system, an IEEE 9-bus system and a 19-generator 42-bus test system. The estimation accuracy of the rotor angle using ISCKF method is increased by 6.8–36.54% when compared to that of the CKF method. Similarly, the improvement in accuracy is 4.4–28.57% for estimation of speed deviation.

Overview of Various Voltage Control Technologies for Wind Turbines and AC/DC Connection Systems

Wind power generation is one of the mainstream renewable energy resources. Voltage stability is as important as the frequency stability of a power system with a high penetration of wind power generation. The advantages of high-voltage direct current (HVDC) transmission systems become more significant with the increase of both installed capacity and transmission distance in offshore wind farms. Therefore, this study discusses various voltage control methods for wind turbines and HVDC transmission systems. First, various voltage control methods of a wind farm were introduced, and they include QV control and voltage droop control. The reactive power of a wind turbine varies with active power, while the active power from each wind turbine may be different owing to wake effects. Thus, QV and voltage droop control with varying gain values are also discussed in this paper. Next, the voltage control methods for an HVDC transmission system, such as power factor control, voltage control, and Vac-Q control, are also summarized and tested in this study. When a three-phase short circuit fault occurs or a sudden reactive power load increases, the system voltage would drop immediately. Thus, various voltage control methods for wind turbines or HVDC can make the system’s transient response more stable. Therefore, this study implemented the simulation scenarios, including a three-phase short circuit fault at the point of common coupling (PCC) or a sudden increase of reactive power load, and adopted various voltage control methods, which aim to verify whether additional voltage control methods are effective to improve the performance of transient voltage. The voltage control method has been implemented in PSCAD/EMTDC, and the simulation results show that the QV control performs better than the droop control. In addition, when applying the voltage control technique during a three-phase fault, transient voltage nadir can be improved through either an HVDC transmission system or an AC transmission system.

Three-phase fault analysis of power system transient stability based on TCSC controller using FPA for its location

Preventing the power system from becoming overloaded and under stress to the point where it is on the verge of reaching the limits of its transient stability due to high power consumption. This paper proposed the dynamic security assessment for transient stability using Thyristor controlled series capacitor (TCSC) devices controller. The stability criteria are based on the severity indices for analyzing the fault in the power system. The index uses the time domain analysis simulation, making it easier and simpler to implement for the system operators to better prepare for potential disturbances by anticipating how power systems will behave. The optimal location and parameters setting of the TCSC was determined by Flower Pollination Algorithm (FPA) due to its higher convergence rate. The proposed index is tested on the IEEE 14-bus system and further discusses the effect of a three-phase short circuit fault, different fault locations, and fault clearing method. An analysis is done to determine how the short circuit faults on lines affect the transient voltage stability of the load bus and generator bus in the system. The findings show that by employing TCSC, the voltage drop was acceptable improved and stability margins were greatly increased.

Analysis of VSC-HVDC support capability for power grids with large-scale renewable energy and multi-infeed HVDC links

Henan Power Grid is located in the north of Central China Power Grid. During its energy transition, thermal power units will be decommissioned on a large scale. Therefore, the scale of the new energy grid connection and regional external power will be further greatly increased to match the load growth demand. Under this background, Henan Power Grid plans to introduce the third HVDC (High Voltage Direct Current). Based on the actual data and the current operation status of Henan Power Grid, this paper proposes an analysis strategy about VSC-HVDC (Voltage Source Converter HVDC) to improve the support capability of the receiving power grid with multi-infeed HVDC. In recent years, VSC-HVDC technology has emerged with the strengths of flexible power regulation and strong voltage support. This paper firstly analyzes the VSC-HVDC power transmission characteristics and clarifies the mechanism of the VSC-HVDC power regulation. Then, based on the actual planning of Henan power grid, the influence of two feed-in schemes (LCC-HVDC (Line Commutated Converter HVDC) and VSC-HVDC) on the voltage stability of power grid and the number of subsequent commutation failures of other conventional DC are compared and analyzed under the three-phase short-circuit fault of AC lines near HVDC terminal location by using PSD-BPA simulation software. The results show that the VSC-HVDC scheme can effectively alleviate the voltage fluctuation (duration within 1 s and fluctuation number within 2 times) after the fault and restrain the number of subsequent commutation failures of conventional DC(with 2 times and even none).

Impact of large-scale photovoltaic-energy storage power generation system access on differential protection of main transformer under symmetrical faults

The low voltage ride-through (LVRT) requirements demand large-scale photovoltaic (PV) power generation system remain connected to the grid during faults. It results in considerable impact on the characteristics of fault current. This paper combines charge-discharge characteristics of the energy storage (ES) with PV generation system to enhance the LVRT capability. Based on the inverter control strategy and specific LVRT requirements, fault current characteristics of the PV-ES power generation system is discussed in this paper. In order to analyze the fault characteristic, the fault current expression as three-phase short-circuit faults occurs on both sides of the main transformer is calculated. Furthermore, taking the winding connection of the transformer into account, the ratio of differential current to braking current is further derived to find out the factors influencing the performance of the transformer differential protection. It is found that factors influencing the transformer differential protection include the rated capacity of the PV-ES generation system, fault severity, the length of transmission line and so on. And as the rated capacity of the PV-ES power generation system increase, the transformer differential protection would experience reduced sensitivity or even do not trip. The findings of this paper can lay a foundation for further improvement of the transformer differential protection. The elaborate performance evaluation of transformer differential protection, including the operation condition of the second harmonic braking element, is presented and verified by simulation using MATLAB/Simulink.

Research and Improvement of Electromechanical Transient Performance of Power System Based on SIMULINK

The research on electromechanical transient stability of power systems is of great significance. Analyzing the parameters of the simulation system and its improved system with typical short-circuit faults, this paper studies the transient stability of power systems and its improvement. Firstly, based on the SIMULINK of MATLAB, a double-loop simulation with the single-machine-infinite-bus system is built. The simulation experiments of the system under the circumstances of three-phase short circuit and single-phase grounding short circuit faults are then carried out to analyze the parameters such as limit cutting time and voltage. Besides, this paper explores how the controllable series capacitor compensation device and reducing mechanical power output by prime mover improve the transient stability of the system. Experiments show that the stability after fault is under conditions where the fault is removed before the critical clearing time, which can increase the threshold to gain more response time for relay protection devices. Thus, the value of researching and improving system transient stability is proved.

Optimal Tuning of Power System Stabilizers for a Multi-Machine Power Systems Using Hybrid Gorilla Troops and Gradient-Based Optimizers

This work discusses the production of a novel hybrid algorithm by combining the gorilla troops optimizer (GTO) with the gradient-based optimizers (GBO) approach. The novel approach is called GTO-GBO, it is offered as a useful tool for optimizing the power system stabilizer (PSS) used in the IEEE four-generator, two-area multi-machine power system subjected to a three-phase short-circuit fault. MATLAB/Simulink software was utilized to carry out the assessments. The suggested approach is initially evaluated using multiple benchmark functions with unimodal and multimodal properties. The results are then compared to other competing algorithms (artificial ecosystem optimizer, artificial rabbits optimizer, Coati Optimization Algorithm, and northern goshawk optimization). The comparisons with various algorithms reveal the developed hybrid GTO-GBO algorithm’s considerable promise. This demonstrates the GTO-GBO algorithm’s improved balance of global and local search stages. The proposed GTO-GBO algorithm’s performance is also evaluated by developing an optimum performing PSS for further examination, allowing observation of its capabilities for difficult real-world engineering challenges. To illustrate the applicability and superior performance of the suggested hybrid algorithm for such a complicated real-world engineering problem, the PSS damping controller is formulated as an optimization problem, and the developed GTO-GBO algorithm is used to search for optimal controller parameters. The latter case’s findings are compared to the competitive optimization algorithms where the GTO-GBO demonstrates the efficiency and robustness of this suggested optimization algorithm to enhance power system stability.

Protection of the Future Harbor Area AC Microgrids Containing Renewable Energy Sources and Batteries

A significant share of global carbon emissions is related to marine vessels running solely on fossil fuels. The hybrid or fully electrified marine vessels using battery energy storage systems (BESS) both for onboard propulsion system and for cold-ironing during docking at harbor areas will significantly reduce marine related carbon emissions. However, the transformation of marine vessels’ operations from diesel engines to BESS will necessarily require charging stations and other electric power infrastructure at harbor areas. The sustainable and cheap energy of renewable energy sources like wind turbine generators (WTGs), photovoltaic (PV) systems and related BESS could be used at harbor areas for charging depleted vessel-BESS and supplying power to cold-ironing loads. For this purpose, two new harbor area smart grid or AC microgrid models have been developed by our research group. This paper presents a comprehensive analysis of three-phase short-circuit faults for one of the proposed AC microgrid models using PSCAD/EMTDC simulations. The fault study of harbor area AC microgrid-1 is done for both grid-connected and islanded modes. The main purpose of the fault study is to check if grid-connected mode overcurrent settings of intelligent electronic devices (IEDs) will also be valid for different islanded mode fault cases with different fault current contributions from converter-based distributed energy resources (DERs) including WTG, PV and BESS. The extent of fault current contribution from DERs and BESS to avoid adaptive protection settings and to ensure definite-time protection coordination and fast fuse operations during different islanded modes is investigated.

DC Commutation Failure Analysis for the Sending-Side System Fault in Hybrid UHV Half-Wavelength and UHV DC Transmission System

Commutation failure (CF) caused by the failure which occurs on the sending side of the ultra-high voltage (UHV) half-wavelength AC (HWAC) transmission system is studied. Firstly, a hybrid UHV HWAC and UHV DC transmission system model is built, and the essence of CF is revealed regarding the influences of various factors on occurrence probability of CF. Then, the mechanism of CF of the UHV DC transmission system caused by the fault at the HWAC line in the hybrid system is explored. The steady-state operation characteristics are obtained through characteristic analysis according to the quasi-steady-state model of the HWAC line, and a three-phase short-circuit fault is assumed on the sending-side of a HWAC line and its voltage characteristics are deeply analyzed. In the actual power system, the specific situation of DC CF caused by the fault of the HWAC line is verified and analyzed based on a large quantity of transient stability calculations. Comparative analysis of the effects on UHV DC lines of the faults which occur on different locations of a HWAC line is presented. The conclusions can provide a useful reference and reliable technical support for the development of HWAC system and maintain power grid security and stability.

Research on the Torsional Vibration Response Characteristics of Parallel Operation Steam Turbine Generator Unit Shafting

With the continuous increase of unit capacity and the widespread application of series compensation devices in power transmission systems, the risk of coupling oscillation between units and power grids and between units has increased significantly, which seriously endangers the safe operation of units and power grids. In this paper, the torsional vibration response of each unit after grid failure is calculated by establishing a lumped mass model of the shafting torsional vibration of the parallel unit. The effects of fault type, series compensation degree and fault location on the torsional vibration of parallel unit shafting are studied. The results show that the three-phase short-circuit fault in the grid has a greater impact on the unit; the influence of series compensation degree on the torsional vibration of the shaft system decreases first and then increases; when the transmission line fails, it will produce a certain torsional vibration excitation effect on the shafting of all units; when a short-circuit fault occurs at the outlet of a generator, the torsional vibration excitation of the unit is the largest, but it will also produce a certain degree of torsional vibration excitation to other units in the same network.