Among different sources of alternate energy, wind and solar are two prominent and promising alternatives to meet the future electricity needs for mankind. Generally, these sources are integrated at the distribution utilities to supply the local distribution customers. If the power generated by these sources is bulk, then they are either integrated at the distribution/transmission level or may be operated in an island mode if feasible. The integration of these renewables in the power network will change the fault level and network topologies. These fault levels are intermittent in nature and existing protection schemes may fail to operate because of their pre-set condition. Therefore, the design and selection of a proper protection scheme is very much essential for reliable control and operation of renewable integrated power systems. Depending upon the level of infeed and location of the renewable integration, the protection requirements are different. For low renewable infeed at the distribution level, the existing relay settings are immune from any small change in the network fault current from new incoming renewables. However, bulk renewable infeed requires modification in the existing protection schemes to accommodate the fault current variation from the incoming renewables. For bulk penetration of the renewable, the requirement of modified/additional protection schemes is unavoidable. Adaptive relaying and non-adaptive relaying schemes are discussed in the literature for protection of power networks, which are experiencing dynamic fault currents and frequent changing network topologies. This article presents a detailed review of protection schemes for renewable integrated power networks which includes distribution, transmission and microgrid systems. The merits and demerits of these protection schemes are also identified in this article for the added interest of the readers. The visible scope of advance protection schemes which may be suitable for providing reliable protection for dynamic fault current networks is also explored.

Protection challenges under bulk penetration of renewable energy resources in power systems: A review

Data analytics are now playing a more important role in the modern industrial systems. Driven by the development of information and communication technology, an information layer is now added to the conventional electricity transmission and distribution network for data collection, storage and analysis with the help of wide installation of smart meters and sensors. This paper introduces the big data analytics and corresponding applications in smart grids. The characterizations of big data, smart grids as well as huge amount of data collection are firstly discussed as a prelude to illustrating the motivation and potential advantages of implementing advanced data analytics in smart grids. Basic concepts and the procedures of the typical data analytics for general problems are also discussed. The advanced applications of different data analytics in smart grids are addressed as the main part of this paper. By dealing with huge amount of data from electricity network, meteorological information system, geographical information system etc., many benefits can be brought to the existing power system and improve the customer service as well as the social welfare in the era of big data. However, to advance the applications of the big data analytics in real smart grids, many issues such as techniques, awareness, synergies, etc., have to be overcome.

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Big data analytics in smart grids: a review

During recent decades with the power system restructuring process, centralized energy sources are being replaced with decentralized ones. This phenomenon has resulted in a novel concept in electric power systems, particularly in distribution systems, known as Distributed Generation (DG). On one hand, utilizing DG is important for secure power generation and reducing power losses. On the other hand, widespread use of such technologies introduces new challenges to power systems such as their optimal location, protection devices' settings, voltage regulation, and Power Quality (PQ) issues. Another key point which needs to be considered relates to specific DG technologies based on Renewable Energy Sources (RESs), such as wind and solar, due to their uncertain power generation. In this regard, this paper provides a comprehensive review of different types of DG and investigates the newly emerging challenges arising in the presence of DG in electrical grids.

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Impact of distributed generation on protection and voltage regulation of distribution systems: A review

Review of major approaches to analyze vulnerability in power system

Vulnerability analysis of power systems is a key issue in modern society and many efforts have contributed to the analysis. Complex network metrics for the assessment of the vulnerability of networked systems have been recently applied to power systems. Complex network theory may come in handy for vulnerability analysis of power systems due to a close link between the topological structure and physical properties of power systems. However, a pure topological approach fails to capture the engineering features of power systems. So an extended topological method has been proposed by incorporating several of specific features of power systems such as electrical distance, power transfer distribution factors and line flow limits. This paper defines, starting from the extended metric for efficiency named as net-ability, an extended betweenness and proposes a joint method of extended betweenness and net-ability to rank the most critical lines and buses in an electrical power grid. The method is illustrated in the IEEE-118-bus, IEEE-300-bus test systems as well as the Italian power grid.

Structural vulnerability of power systems: a topological approach

This paper proposes an adaptive protection scheme for distribution systems with distributed generations (DGs). To mitigate the influences on the protection devices by DGs, an online calculation method of fault current under various system operation conditions is presented. By sampling local available measurements in the buses, a proposed optimized estimation method is used to calculate the Thevenin equivalent circuit parameters of the system dynamically. Moreover, the short-circuit current can be calculated accurately to set the overcurrent relay protection value considering the behavior of DGs during the fault. To ensure the accurate operation of the protection devices, a coordinated protection scheme, including primary and backup protection is presented. Performances of the proposed method and scheme have been verified by simulations on a sample distribution system based on PSCAD/EMTDC. The sensitivity and selectivity of the coordination between primary and backup protection are satisfied under different system operation conditions, fault locations, and types.

An Adaptive Protection Scheme for Distribution Systems With DGs Based on Optimized Thevenin Equivalent Parameters Estimation

Seven centrality indexes are first presented for identifying important nodes with topological features of a complex network and electrical characteristics of a power system considered. Then, a criteria importance through intercriteria correlation-based multi-index decision-making method, in which entropy and the Spearman’s rank correlation coefficient are integrated for reflecting the differences and correlations among multiple indexes, respectively, is presented to comprehensively identify the importance degrees of nodes in a given power grid. Finally, the proposed indexes and method are applied to actual Guangdong power system in China, and the results are compared with those attained by single-attribute and multi-attribute evaluation methods.

CRITIC-Based Node Importance Evaluation in Skeleton-Network Reconfiguration of Power Grids

Aiming at eliminating the current drawbacks that exists in condition-based maintenance (CBM) decision-making, such defects as single objective model, difficulty in controlling the process, and individual rather than group decision-making, this paper proposed a multiobjective group decision-making CBM model based on Dempster-Shafer (D-S) evidence theory by establishing maintenance decision-making framework, setting index system and quantifying all the indices. The model takes decision-making indices as evidence sources and maintenance schemes as knowledge framework, solving the problem of difficulty in demarcation of objectives and constraints. Maintenance schemes are achieved according to mean residual life prediction based on maintenance guidance and current condition quantified by health index to estimate the most appropriately maintenance interval. After that, standardized values of indices under each scheme are normalized into mass function of D-S evidence theory. Then, considering comprehensive weights of indices decision-makers, multiobjective group decision-making results of maintenance types, and time intervals are obtained. Finally, a numerical case is studied to illustrate the proposed modeling process, and demonstrates that the model can effectively realize multiobjective group decision-making, as well as considering the intentions of decision makers while all indices can reach global optimum.

Research on Multiobjective Group Decision-Making in Condition-Based Maintenance for Transmission and Transformation Equipment Based on D-S Evidence Theory

In order to analyze the fault trends more accurately, a failure rate model appropriate for general electric power equipment is established based on a nonparametric regression method, improved from stratified proportional hazards model (PHM), which can make maximum use of equipment lifecycle data as the covariates, including manufacturer, service age, location, maintainer, health index, etc. All of covariates are represented in the hierarchy process of equipment health condition, which is beneficial for processing and classifying the lifecycle data into multitype recurrent events quantitatively. Meanwhile, based on new definitions of single health cycle and time between events, recurrent inspecting events distributed with martingale process can correspond with event-specific failure function during equipment lifecycle. On this occasion, more inspecting events can be utilized in a complete cycle to predict potential risk and assess equipment health condition. Then, stratified nonparametric PHM is employed to build the multitype recurrent events-specific failure model appropriate for competing risk problem toward interval censored. Lastly, the example in terms of transformers demonstrates the modeling procedure. Results show the well asymptotic property and goodness-of-fit tested by both of graphical and analytical methods. Compared with existing failure models, such as age-based or CBF model, this improved nonparametric regression model can mine lifecycle data acquisition from asset management system, depict the failure trend accurately considering both individual and group features, and lay the foundation for health prognosis, maintenance optimization, and asset management in power grid.

Nonparametric Regression-Based Failure Rate Model for Electric Power Equipment Using Lifecycle Data

In this paper, a distance relay-based wide-area backup protection (WABP) algorithm for transmission lines is presented. The proposed WABP collects the statuses of zone 2 and zone 3 distance relays in local substation and immediate neighboring substations. When a fault has occurred, the WABP decides whether the fault is on the protected transmission line or somewhere else. Then, it determines the appropriate time delay of tripping and acts in coordination with conventional distance relays. With the proposed WABP equipped, the setting of conventional distance relays can be simplified. The requirement of coordination between the conventional relays can be loosened and the difficulty of setting calculation can be reduced. Simulation results show that the proposed WABP can coordinate with conventional distance relays set by different methods, and it can correctly detect faults and help to reduce blackout area with fault tolerance.

Huifang Wang

Papers

An Adaptive Protection Scheme for Distribution Systems With DGs Based on Optimized Thevenin Equivalent Parameters Estimation

CRITIC-Based Node Importance Evaluation in Skeleton-Network Reconfiguration of Power Grids

Research on Multiobjective Group Decision-Making in Condition-Based Maintenance for Transmission and Transformation Equipment Based on D-S Evidence Theory

Nonparametric Regression-Based Failure Rate Model for Electric Power Equipment Using Lifecycle Data

Research on a Distance Relay-Based Wide-Area Backup Protection Algorithm for Transmission Lines