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

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.

The prominence of incorporating the renewable energy resources in a power system via microgrids has increased in the recent years, which impose a caution on conventional protection schemes. Protection schemes proposed earlier use local measurements, but fault classification for selective phase tripping using wide area measurements for microgrid has not been reported so far. This paper presents a wide area monitoring and protection of microgrid with distributed generations (DGs) using modular artificial neural networks (MANNs) for the fault detection and classification without affecting the relays in non-faulty or healthy sections of the microgrid. The distinct characteristics of the microgrid sort the proposed methodology into two stages. In stage 1, ANN 1 is developed to identify the operating mode of microgrid, whether it is operating in grid-connected mode (GCM) or islanded mode (IM). In stage 2, there are two MANNs corresponding to GCM and IM. Each MANNs consists of three separate ANNs for fault detection, classification, and section identification. A standard IEC 61850-7-420 microgrid with DGs (wind and photovoltaic) penetration is modeled in MATLAB/Simulink. The three-phase voltages and currents are measured with time synchronization considering the microphasor measurement units located at each bus. The extensive study includes different simulation scenarios such as shunt faults, high impedance fault, and dynamic situations like connection/disconnection of DGs/distribution lines. The results confirm the efficacy of the proposed methodology.

The fault location problem has been tackled mainly through impedance-based techniques, the travelling wave principle and more recently machine learning algorithms. These techniques require both current and voltage measurement. In the case of impedance-based methods they can provide multiples solutions. In the case of the travelling wave approach it usually requires high sampling frequency measurements together with sophisticated identification algorithms. Machine learning techniques require training data and re-tuning for different grid topologies. This paper proposes a new fault location method based on the fault’s transient intermediate frequency response of the system immediately after a fault occurs. The transient response is characterized by the travelling wave phenomenon together with intermediate frequencies of oscillation, which are dependent on the faulted section and the fault location. In the proposed fault location solution, an offline methodology identifies these intermediate frequencies and their dependency on the fault location is fitted using a polynomial regression. The online fault location is performed using those polynomial regressions together with voltage measurements from the system and simple signal processing techniques. The full method is tested with an EMT simulation in PSCAD, using the exact frequency dependent model for underground cables.

In recent years, the networked distribution system (NDS), which is normally connected to the distribution line (DL), was actively studied as the topology of the future distribution system for reasons such as improving supply reliability, improving line utilization, and increasing the capacity of distribution generators (DGs). However, the NDS creates new issues in terms of protection coordination because of its bidirectional power flow and fault current flow. The issues associated with conventional protection schemes in the NDS include malfunction of protective devices due to bi-directional fault currents and failure of protection coordination due to communication failures between protective devices. When applying a conventional protection method in the NDS, the protection schemes become complicated, and there is a risk of protection coordination failure due to communication failure between protective devices. To solve this problem, this paper proposes an effective and innovative non-communication-based protection algorithm for protection coordination in the NDS. The proposed protection algorithm utilizes fault impedance characteristics, which allow not only determination of whether a fault occurred, but also the ability to identify the exact fault point. Therefore, the proposed method is expected to be sustainably utilized and contribute to developing protection schemes and devices in various system topologies and scenarios in the future. Additionally, this paper addresses the overall concept of hardware-in-the-loop simulation (HILS) and directly verifies the proposed protection algorithm using HILS. Therefore, this study establishes a sustainable foundation for future research on protection coordination using HILS.

Microgrids are the localized grids which consists of number of distributed generators (DGs) with the distribution system. Introduction of DGs into distribution system cause changes in the fault current levels & directions, thus results in inaccurate operation of the existing protection system. Fault currents in the system also varies significantly following the transition of grid-connected and islanded operational modes of microgrid. Procuring a coordinated protection system which operates accurately in DGs integrated scenario is still a challenging aspect for the planners. In this paper, protection system has been proposed which is suitable for both grid-connected and islanded operational modes of microgrid. Differential evolution (DE) algorithm has been used for achieving the proper coordination of directional overcurrent relays (DOCR) in the distribution systems. IEEE-9-bus distribution system integrated with four DGs have been analysed in this paper. Discrete plug setting (PS) and time multiplier setting (TMS) has been obtained which are feasible for numerical relays. Obtained optimized relay settings provide efficient and accurate operation of relays with minimum operating time.

Deep spatiotemporal feature fusion using CNN-LSTM autoencoder for real-time, phase-aware anomaly identification and localization in high-voltage power transmission networks

One of the factors that affect the level of fault currents is the number of short-circuit MVA sources present during the fault. A distribution system with distributed generators (DGs) is a multi-source system, in which DGs can be connected or disconnected to meet the high or low load requirements respectively. Also, during fault conditions, DGs can get disconnected due to their low fault ride-through capabilities. These changes in connections change the number of DGs and the operational status of the system, which in turn change the fault currents seen by relays and the ranges of maximum and minimum fault currents for which the relays settings work coordinately. This paper realizes that an increase in the proliferation of DGs makes the relay coordination problem a highly constrained optimization problem, and changes in the number of DGs make the problem more complex, which can decelerate the overall performance of relays. The aim of this paper is to reduce the complexity and design a fast, robust, and adaptive protection scheme which can efficiently work in the variable environment of the DG-distribution system. This paper proposes a novel constraints reduction-based relay coordination method which selects a small set of constraints out of large set of constraints while determining the optimal relays settings. The relay coordination problem is formulated as a linear programming problem. The performance of the proposed method is tested on the both configurations, radial and meshed, of the IEEE 38-bus distribution system. Comparative studies have been conducted to highlight the advantages of the proposed approach under changing system’s configuration with variable locations and sizes of DGs.

Since microgrids should be able to smoothly operate in two distinct modes—grid-connected and islanded, their fault currents can widely fluctuate depending on the operational mode. When the microgrid is connected to the grid, the highest fault current, by far, is supplied by the utility grid. In this mode, the fault current contribution from distributed energy resources (DERs) is less than 20%. However, when the microgrid switches to the islanded mode, the fault current contribution from the utility grid is lost and DERs are the sole fault current sources. Thus, the overall fault current in the islanded mode is multiple times lower when compared to the grid connected mode. Moreover, most of the DERs are inverter-based, with limited fault currents, which further reduces the overall fault current in the islanded mode. With the rapid rise of the microgrid penetration around the globe, this phenomenon can adversely influence the relay protection, and thus the microgrid fault current needs to be precisely analyzed. Therefore, the main purpose of this paper is to thoroughly analyze the fault current differences in two distinct operation modes of a microgrid, and to consequently derive conclusions regarding the required improvements in fault calculations and relay protection analysis in emerging microgrids. A representative microgrid test bed is developed and modelled using the in-house developed software as well as in a state-of-the-art hardware-in-the-loop environment. Several different short-circuit faults were simulated and analyzed in both grid-connected and islanded modes. The results show that the fault currents significantly differ depending on the operating mode, and thus highly influence the protection system. Moreover, test results show that the fault calculation algorithms aimed at radial distribution grids, mostly used for microgrid fault calculations in the available literature, need to be further improved to provide precise and time-efficient results when the emerging microgrids are considered. These results provide a valuable insight into the current state of the microgrids’ fault calculation and protection and reveal several important directions for future research.

A distance relay scheme is commonly used for backup protection. This scheme, called a step distance protection, is comprised of 3 steps for graded zones having different operating time. As for the conventional step distance protection scheme, Zone 2 can exceed the ordinary coverage excessively in case of a transformer protection relay especially. In this case, there can be overlapped protection area from a backup protection relay and, therefore, malfunctions can occur when any fault occurs in the overlapped protection area. Distance relays and overcurrent relays are used for backup protection generally, and both relays have normally this problem, the maloperation, caused by a fault in the overlapped protection area. Corresponding to an IEEE standard, this problem can be solved with the modification of the operating time. On the other hand, in Korea, zones are modified to cope with this problem in some specific conditions. These two methods may not be obvious to handle this problem correctly because these methods, modifying the common rules, can cause another coordination problem. To overcome this problem clearly, this paper describes an improved backup protection coordination scheme using an IEC 61850-based distance relay for transformer backup protection. IEC 61850-based IED(Intelligent Electronic Device) and the network system based on the kernel 2.6 LINUX are realized to verify the proposed method. And laboratory tests to estimate the communication time show that the proposed coordination method is reliable enough for the improved backup protection scheme.

The traditional distribution systems are radial and have unidirectional power flow. The overcurrent protection system of these networks is negatively affected by Distributed Generation (DG) units. The time and current coordination of protection devices of these systems is the most important concern in the case of high DGs penetration. Actually, DGs connection and disconnection change the short circuit level of feeders and disturb the coordination of protection devices. So, new protection schemes should be proposed which must not to be affected by DGs and should work properly in both islanded and grid connected operation modes of the micro-grid. In this paper, an adaptive protection scheme, based on fault location, is proposed for smart micro-grids. The functionality of each protection device is adaptively selected based on detected network topology and fault type. The proposed solution is simulated in the SimPower software. The results show the efficiency of the proposed protection scheme which cannot be affected by DGs.

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.

In this paper a novel concept of improving power quality (PQ) in low voltage networks with distributed generation (DG) is proposed. In contrast to traditional methods which require the application of dedicated resources to compensate for power quality disturbances, the proposed idea is simply to form a microgrid (MG) capable to isolate from the utility grid and operate islanded when a disturbance occur. In the paper conditions for island creation are discussed and a control strategy is presented for a small-scale active network with microturbine, renewable energy sources, loads and storage system. The strategy assumes using energy storage unit as a grid forming unit for islanded operation and a central controller for supervising the network operation in grid-connected and islanded modes. The part of strategy is islanding condition detection method which is based on immunity curve defined for the considered network. Performance of the proposed strategy is presented as a reaction of the network on voltage dips, however the idea is applicable to any PQ disturbance of unacceptable level occurring in the utility grid. For the considered network a simulation model has been developed using PSCAD/EMTDC platform. Simulation results are presented in the paper which illustrate the operation of the control system and show the microgrid behavior after transition from grid-connected to islanded operation mode.

The complexity of an active distribution system with distributed generation (DG) is increasing day-by-day. Therefore, a reliable protection system is very necessary to satisfy customer demand. Apart from main grid supply, active sources are also available near load centers due to which traditional protection schemes fails to function properly. The magnitude of fault current during grid connected mode of microgrid, is much higher than islanded operation. Therefore, in most of the previous works, overcurrent protection crashes if its pickup current value is not changed when microgrid is shifted to islanded mode. In this paper, the current, voltage and frequency data sampled through PMU is processed to protect the system in both the operating modes. A centralized protection scheme is employed that takes frequency data and voltage phasor to differentiate between islanding and fault condition. Further, it detects the faulted feeder and sends trip command to respective relays within a tolerant time. This method is devised to work as backup protection when main utility grid is available. However, it can work as a primary protection during islanded mode, when local overcurrent relay fails to operate due to settings based on grid connected mode. A standard IEEE 15 bus system modeled in EMTP-RV is taken as test system for every analysis.

This paper proposes a new zonal protection scheme using dual setting directional overcurrent relays, applied to micro-grids with high DG penetration, which does not require a communication infrastructure. The proposed protection scheme is formulated as a nonlinear programming problem where the main objective is to determine the optimal relay forward and reverse settings to minimize the relay overall operating time. The proposed protection scheme is applied to an IEEE 33-bus distribution system with synchronous-based DG units in an islanded mode. The performance of the proposed scheme is compared against other protection schemes for micro-grids that rely on overcurrent relays. Results show that, for micro-grid systems, dual setting directional overcurrent relays are capable of mitigating protection coordination failure without the need for communication, along with a capability to handle bidirectional fault current flow, and thus making such relays more suitable for synchronous-based micro-grids.

In a microgrid, the overcurrent relays see significant variation in the short-circuit currents during transition between grid-connected and islanded modes of operation. Further, with the disconnection of one or more distributed generators (DGs), the changes in the short-circuit currents are observed by the relays. As a consequence, the existing protection scheme may either delay the relay operation or fail to operate. This paper proposes an optimal and single protection scheme suitable for all operating modes of microgrid along with every type of phase faults in the system, i.e., three-phase symmetrical ( $3\text{-}\phi$ ), line-to-line, and double line-to-ground faults. The optimal setting of the directional overcurrent relays is obtained using a metaheuristic-based optimization algorithm. Moreover, the proposed scheme is validated using GE Multilin, model-750/760, overcurrent relay in ETAP (industrial simulation software) on the modified IEEE 9-bus 4-DG microgrid.