AC Micro Grid Fault Analysis

The dynamic behavior of microgrid compromises the security and selectivity in conventional protection schemes. Islanding mode of operation provides continuous power supply to customers. Mesh configuration of microgrid can further improves the reliability. However, protection of mesh microgrid is a challenging task especially the isolation of faulted part only with rest of the system in operation. This paper presents a communication assisted protection scheme using negative sequence based voltage and current information of a microgrid. Using the change in angle difference of negative sequence voltage and current from pre-fault to fault case, method identifies the fault is internal or external. A hardware setup is established in the laboratory and performance of the relay algorithm is tested. Arduino uno microcontroller board is used as relay processor and XBee module is used for wireless communication.

To design a perfect protection scheme is a big challenge for microgrid (MG) network implementation because it can operate either grid connected mode neither islanding mode. Due to distributed generation (DGs) resources the fault current always varied steadily hence the system parameters. This research focus on two vital properties of microgrid: peer-to-peer and plug-and-play to avoid sophisticated communication network for microgrid adaptive protection schemes. A microgrid model has been proposed by conventional protection scheme and addressing all possible drawbacks along with distributed energy resources. Whole microgrid is divided into different protection zone to identify perfect fault detection techniques by analyzing corresponding system parameters. Moreover, transformer protection also considered in new proposed protection scheme.

This paper proposes a pattern recognition based differential spectral energy protection scheme for ac microgrids using a Fourier kernel based fast sparse time-frequency representation (SST or simply the sparse S-Transform). The average and differential current components are passed through a change detection filter, which senses the instant of fault inception and registers a change detection point (CDP). Subsequently, if CDP is registered for one or more phases, then half cycle data samples of the average and differential currents on either side of the CDP are passed through the proposed SST technique, which generates their respective spectral energies and a simple comparison between them detects the occurrence and type of the fault. The SST technique is also used to provide voltage and current phasors and the frequency during faults which is further utilized to estimate the fault location. The proposed technique as compared to conventional differential current protection scheme is quicker in fault detection and classification, which is least effected from bias setting, has a faster relay trip response (less than one cycle from fault incipient) and a better accuracy in fault location. The significance and accuracy of the proposed scheme have been verified extensively for faults in a standard microgrid system, subjected to a large number of operating conditions and the outputs vindicate it to be a potential candidate for real time applications.

A differential protection scheme for the ring microgrids based on the power change rate of the bus is proposed. By setting the power change rate on both sides of the bus as the differential amount, the power change rate is maximized at the moment of short-circuit, which can immediately indicate whether a fault has occurred. Compared to the protection scheme that uses the current for fault identification, the proposed scheme reduces the time for the fault current to increase to the action threshold, saves the time required for fault detection. Moreover, it is proportional to the square of the current, and the higher orders increase the speed of the change rate, meanwhile, it is proportional to the short-circuit impedance which broadens the fault identification range and improves the protection sensitivity. Finally, the results of simulations prove that the proposed protection scheme has improved speed, sensitivity, and interference resistance while maintaining good selectivity for differential protection.

The low-voltage dc (LVDC) microgrid possesses numerous benefits and their penetration in the power system has increased rapidly in recent years. However, the detection of faults in the LVDC microgrid is a challenging issue due to the large magnitude of fault currents and fault-level variation in the microgrid. The performance of the recent current and its derivative-based protection scheme is limited in case of faults in the islanding mode of operation, different microgrid topologies, varying distributed generations (DGs) penetration, and against the measurement noise. This article presents an enhanced differential protection scheme for LVDC microgrid integrated with multiple DGs and storage. The differential current and its first derivative are processed through the decision tree (DT) algorithm for fault detection and the K-nearest neighbor (KNN) technique is utilized for fault classification. The robustness of the proposed protection scheme is tested for different fault types and fault conditions with variation in microgrid topology and operating conditions. The impact of the intermittent and volatile nature of the DGs, the presence of measurement noise, and assessment during external faults and critical no-fault cases have been investigated. The proposed scheme is tested on the MATLAB/ SIMULINK and validated on the Typhoon HIL platform for the assessment of real-time performance. The test results show that the proposed scheme can detect and classify faults with high accuracy and faster response time and, thus, can be a potential candidate for providing dependable protection measures for LVDC microgrids.

The integration of DC networks including DC microgrids (DCMGs) into power systems is rapidly increasing. This is notably attributed to the distinctive fault current characteristics arising from inverter-based distributed generation resources in DCMGs, which differentiate them from conventional networks. As a result, the protection of DCMGs presents considerable challenges. Leveraging the recent strides in artificial intelligence, this paper introduces a novel multi-agent-based protection scheme for DC microgrids. Subsequently, three fault classification approaches are proposed in an intelligent protection scheme platform, employing diverse machine learning-based methods as a backup protection for fault detection and the main protection for fault location. The proposed protection scheme uses three main protection layers—namely, equipment, substation, and system—each endowed with specialized agents. In this way, the first and second fault classification approaches employ classifiers based on machine learning algorithms, such as Support Vector Machine (SVM) and Decision Tree (DT), to ascertain the microgrid status. Subsequent fault location is accomplished through various neural networks dedicated to the fault location. In the third approach, three Deep Neural Networks (DNNs) are proposed for fault classification, prompting the exclusion of classifiers from the substation layer due to the heightened training proficiency of DNNs. Intelligent Electronic Devices (IEDs) are placed at the beginning of the lines and send voltage and current information to the substation layer. Communication among agents and layers is performed by the IEC-61850 protocol. Comprehensive simulations and analyses are conducted using DIgSILENT, MATLAB, and Python (TensorFlow platform and Keras library) software. The findings underscore the efficacy of the proposed scheme and Fault Detection and Location (FDL) approaches, affirming their capability for precise fault classification and location determination.

Communication-less protection scheme for AC microgrids using hybrid tripping characteristic

A novel protection scheme for low voltage DC microgrid using inductance estimation

Protection of microgrid has become challenging due to the hosting of various actors such as distributed generation, energy storage systems, information and communication technologies, etc. The main protection challenges in the microgrid are the bi-directional power flow, protection blinding, sympathetic tripping, change in short-circuit level due to different modes of operation, and limited fault current contribution by converter-interfaced sources. This paper presents a comprehensive review of the available microgrid protection schemes which are based on traditional protection principles and emerging techniques such as machine learning, data-mining, wavelet transform, etc. A categorical assessment of the reviewed protection schemes is also presented. The key findings of the paper suggest that the time-domain and communication-assisted protection schemes could be suitable solutions to address the identified protection challenges in the microgrid.

The DC microgrid has become a typical distribution network due to its excellent performances. However, a well‐designed protection scheme still remains to be a challenge for DC microgrids. This paper proposes a fault distance estimation‐based protection scheme for DC loop‐type microgrids relying on two‐terminal electrical quantities. Different from the traditional methods, a small inductor is implemented at each head of the line instead of obtaining the derivative of fault current using current difference value. Thus, the derivative of currents can be calculated accurately with the measured voltages on the small inductors during faults. The presented protection method is able to realise fault location and fault isolation quickly and accurately. Furthermore, it is immune to fault resistances. The presented protection scheme has been tested and verified through PSCAD/EMTDC simulations. The results prove that the new protection scheme possesses the excellent performance.

The behavior of anomalous dielectrics : H. Jordan. ( Deutsch. Phys. Gesell. Verh., xiv, 9, 451)

A good protection system is a backbone of any grid. With the injection of distributed generators in the grid, the traditional protection system consisting of overcurrent relay is not sufficient to protect the system. It is therefore very important to understand the level of fault currents in the micro grids when they are connected to the grid and when they operate independently in the islanded mode. In this paper a micro grid consisting of different distributed generators such as wind turbine, solar panel, the fuel cell along with DC to DC converter and a 3-ϕ inverter feeding a 3-ϕ AC load is simulated in MATLAB. The simulated microgrid has been subjected to various faults in both grid connected and islanded mode and fault current levels are discussed in detail. The analysis done in this work is helpful in designing an effective and reliable protection scheme for the hybrid microgrid when operated in islanded and grid connected modes.

Microgrid protection schemes play a vital role in ensuring the reliability and efficiency of power distribution in urban and rural areas, especially as renewable distributed energy resources are increasingly integrated. This paper aims to provide a comprehensive analysis of existing microgrid protection schemes, discussing their advantages and limitations and highlighting key challenges and opportunities for future research. As microgrid systems become increasingly common, the management of power flow in small-community networks equipped with intelligent electronic devices, non-linear loads, and multiple distributed generation sources becomes more complicated. In order to address these challenges, coordination of protective schemes is required to prevent overload and damage to equipment. Firstly, the study discusses microgrid definitions and functional categories, highlighting their benefits and drawbacks. An analysis of microgrid protection literature includes adaptive protection systems as intelligent methods to address coordination challenges. Secondly, this review classifies microgrid protection techniques as modified, new knowledge-based and conventional schemes and provides a systematic analysis of optimization approaches. The study also examines the essential problems associated with the coordination of protective relays within microgrids. Finally, examining the current state of microgrid protection to identify the key research directions and opportunities for future development in this rapidly advancing field. The findings of this comprehensive analysis highlight the importance of effective microgrid protection in ensuring a stable and sustainable energy future.

The paper focuses on the study of the protection problems arising in a MV autonomous micro-grid starting from the analysis of its physical and electrical characteristics in order to asses through numerical simulations how they influence the design of suitable protection schemes. From the viewpoint of distribution operators, it is advisable for technical and economical reasons to consider as far as possible protection devices based on the same principles used for fault clearing and isolation in a traditional distribution network, bearing in mind that any micro-grid protection scheme has to be compatible with the general scheme implemented in the main MV distribution system to which the micro-grid is connected. (5 pages)

Microgrid protection schemes are different from those used in conventional distribution networks. With the incorporation of distributed generation (DG), and the ability for bi-directional power flow and island operation; the fault current and delay parameters of protective relays need to be recalculated and updated in response to the dynamic operation of microgrid. Performance evaluation (e.g. fault clearance time and recovery time) and parameter estimation (fault current and trip delay) for such a protection scheme have been difficult because they require comprehensive modeling of electrical network, IED behaviors, and IEC61850-based communication. In this paper, we present a centralized scheme with detailed modeling and co-simulation of all these aspects. We also demonstrate how the analysis of the simulation results helps overcoming the forth-mentioned difficulties.