Cyber-physical attacks and defences in the smart grid: a survey <s> Introduction <s> This paper describes basic principles and philosophy for wide-area protection schemes, also known as remedial action schemes (RAS) or system protection schemes (SPS). In the areas of power system automation and substation automation, there are two parallel trends in different directions: centralization and decentralization. More and more functions are moved from local and regional control centers toward the central or national control center. At the same time we also observe more and more "intelligence" and "decision-power" moving closer toward the actual power system process. We also see a great deal of functional integration, i.e., more and more functionality enclosed in the same hardware. This raises discussions concerning reliability (security and dependability). The main targets for this paper is therefore to: 1) sort out the terminology used in this area; 2) describe different application areas and related requirements; 3) illustrate different design principles-"top-down", "bottom-up", hierarchy, flat, etc., for different applications; and 4) identify similarities and differences between classic equipment protection and system protection-concerning philosophy as well as concerning product and system design. The theme of the paper is on the use of information technology to obtain more flexibility and smartness in power-system controls. <s> BIB001 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Introduction <s> For 100 years, there has been no change in the basic structure of the electrical power grid. Experiences have shown that the hierarchical, centrally controlled grid of the 20th Century is ill-suited to the needs of the 21st Century. To address the challenges of the existing power grid, the new concept of smart grid has emerged. The smart grid can be considered as a modern electric power grid infrastructure for enhanced efficiency and reliability through automated control, high-power converters, modern communications infrastructure, sensing and metering technologies, and modern energy management techniques based on the optimization of demand, energy and network availability, and so on. While current power systems are based on a solid information and communication infrastructure, the new smart grid needs a different and much more complex one, as its dimension is much larger. This paper addresses critical issues on smart grid technologies primarily in terms of information and communication technology (ICT) issues and opportunities. The main objective of this paper is to provide a contemporary look at the current state of the art in smart grid communications as well as to discuss the still-open research issues in this field. It is expected that this paper will provide a better understanding of the technologies, potential advantages and research challenges of the smart grid and provoke interest among the research community to further explore this promising research area. <s> BIB002 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Introduction <s> The development of a trustworthy smart grid requires a deeper understanding of potential impacts resulting from successful cyber attacks. Estimating feasible attack impact requires an evaluation of the grid's dependency on its cyber infrastructure and its ability to tolerate potential failures. A further exploration of the cyber-physical relationships within the smart grid and a specific review of possible attack vectors is necessary to determine the adequacy of cybersecurity efforts. This paper highlights the significance of cyber infrastructure security in conjunction with power application security to prevent, mitigate, and tolerate cyber attacks. A layered approach is introduced to evaluating risk based on the security of both the physical power applications and the supporting cyber infrastructure. A classification is presented to highlight dependencies between the cyber-physical controls required to support the smart grid and the communication and computations that must be protected from cyber attack. The paper then presents current research efforts aimed at enhancing the smart grid's application and infrastructure security. Finally, current challenges are identified to facilitate future research efforts. <s> BIB003 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Introduction <s> The Smart Grid, regarded as the next generation power grid, uses two-way flows of electricity and information to create a widely distributed automated energy delivery network. In this article, we survey the literature till 2011 on the enabling technologies for the Smart Grid. We explore three major systems, namely the smart infrastructure system, the smart management system, and the smart protection system. We also propose possible future directions in each system. colorred{Specifically, for the smart infrastructure system, we explore the smart energy subsystem, the smart information subsystem, and the smart communication subsystem.} For the smart management system, we explore various management objectives, such as improving energy efficiency, profiling demand, maximizing utility, reducing cost, and controlling emission. We also explore various management methods to achieve these objectives. For the smart protection system, we explore various failure protection mechanisms which improve the reliability of the Smart Grid, and explore the security and privacy issues in the Smart Grid. <s> BIB004 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Introduction <s> A communication infrastructure is an essential part to the success of the emerging smart grid. A scalable and pervasive communication infrastructure is crucial in both construction and operation of a smart grid. In this paper, we present the background and motivation of communication infrastructures in smart grid systems. We also summarize major requirements that smart grid communications must meet. From the experience of several industrial trials on smart grid with communication infrastructures, we expect that the traditional carbon fuel based power plants can cooperate with emerging distributed renewable energy such as wind, solar, etc, to reduce the carbon fuel consumption and consequent green house gas such as carbon dioxide emission. The consumers can minimize their expense on energy by adjusting their intelligent home appliance operations to avoid the peak hours and utilize the renewable energy instead. We further explore the challenges for a communication infrastructure as the part of a complex smart grid system. Since a smart grid system might have over millions of consumers and devices, the demand of its reliability and security is extremely critical. Through a communication infrastructure, a smart grid can improve power reliability and quality to eliminate electricity blackout. Security is a challenging issue since the on-going smart grid systems facing increasing vulnerabilities as more and more automation, remote monitoring/controlling and supervision entities are interconnected. <s> BIB005
Cyber-physical systems (CPSs) are inducing profound changes in the modern society. Composed of computation, communication, and physical systems and processes, CPS integrate, and coordinate heterogeneous components with increasing intelligent, interactive, and distributed operations in the modern critical infrastructures. The emerging smart grid, being one of the most complex CPS ever built in history, witnesses such transformations during the ongoing integration of power and energy systems with information and communication technologies (ICTs)  . The fundamental changes in this critical infrastructure are leading toward far-reaching impacts on not only the energy, but also a number of critical interdependent sectors. The smart grid encompasses complex systems of power, energy, control, sensory, computing, and communication. The complexity and heterogeneity in this architecture have underscored the potential challenges to its security and resilience. On one hand, the interconnection of bulk power systems is complicating the protection against inherent physical vulnerabilities therein. On the other hand, the cyber-integration requires substantial investments on security designs and upgrades against unforeseen patterns and threats from the cyberspace. The collective research effort on cybersecurity and physical security have been striding fast and fostering a new area of CP security for the smart grid BIB003 . An essential and primary focus of CP security is the investigation of complex attack schemes. Powered by the information and computation resources in the cyberspace, malicious attackers can conceive intrigue schemes to exploit both known and zero-day vulnerabilities in the smart grid. Compared with traditional power system and communication network security, CP security is still in an 'infancy' period. However, existing investigations have already revealed some catastrophic consequences that are largely unprepared by the government, industry, and public. The assessments of vulnerability and resilience against the CP attacks are providing the cornerstones for comprehensive defensive plans and emergency responses for the critical electrical power infrastructure. In the meantime, the investigations of attack threats and the developments of defence strategies remain far from comprehensive. Inspections of cyber and physical security are essential for the security of smart grid, but neither direction alone is able to provide inclusive understandings and solutions without incorporating the other. Although many of the revealed attack threats are accompanied with protection, detection, or mitigation strategies, a large portion of the uncovered threats still remain to be addressed. Furthermore, the ongoing developments and deployments of CPS and technologies in the smart grid are continuously unveiling new vulnerabilities and schemes; the known threats also merit prompt re-evaluation in line with the new progresses. It has thereby become a task of paramount importance to keep up with the latest advances along this research frontier. To this end, this paper aims to provide a review on the state-of-the-art of CP attack schemes and defence strategies in the smart grid. Instead of enumerating all potential attack schemes, this paper will focus on the most critical schemes, where attackers have the potential to significantly disrupt or damage power system operations. The victims emerge from the critical assets in generation and transmission systems as well as the field devices of distribution systems and customers. As shown in this paper, the attack threats are substantial and prevalent, yet they may still just be the tip of the iceberg. We hope to facilitate the understanding of existing and emerging vulnerabilities and to inspire innovations and solutions for the security and resilience of the smart grid as well as other critical CPS infrastructures. In the rest of this paper, we first provide an overview of the CP security problems in the smart grid in Section 2, which will introduce the smart grid as a CPS infrastructure and the need for an integrative perspective of CP security. In Section 3, we will review the critical CP attack schemes revealed by extensive investigations. Section 4 reviews the defence strategies developed against these revealed attack threats. Section 5 discusses the challenges and opportunities to address the security of smart grid based on the existing attack schemes and defence strategies. The conclusions are provided in Section 6. traditional paradigm of power system operations, the electricity is generated in power plants and delivered along the transmission systems to customers in the distribution systems. Energy management systems (EMSs) located in control centres monitor and control this unidirectional process through supervisory control and data acquisition (SCADA) systems. The SCADA systems are usually hosted on dedicated communication infrastructures comprising wide-area networks, field area networks, and local area networks. Networked sensors in the system collect measurements, e.g. voltage and currents, and transmit the data to the control systems through remote terminal units (RTU) in the SCADA system. The RTU are also responsible for the operation of actuators to adjust topology and parameters of the dynamic system. The physical systems of generation, transmission, and distribution are interconnected through transmission lines and substations deployed in the field. On top of these infrastructures, regional transmission organisations and independent system operators coordinate the system operations among service providers and consumers in the electricity market. An overview of the entire smart grid infrastructure has been shown in Fig. 1 , which contains seven domains of generation, transmission, distribution, operation, electricity markets, service providers, and customers, as defined by the National Institute of Standards and Technologies (NIST)  . Innovative systems and technologies in the smart grid have been transforming the traditional power systems in numerous areas BIB002 BIB004 BIB005 . The growing integration of renewable energy systems (RESs) improves the sustainability and economics of generation systems. Distributed energy resources (DERs) allow customer-side power generation and management with more flexibility and reliability, reshaping the existing patterns of power flows from unidirectional into bidirectional. The phasor measurement unit (PMU) utilises global positioning system (GPS) to provide more frequent, accurate, and reliable synchronised measurements in the transmission systems, enabling the implementation of wide-area monitoring, protection, and control (WAMPAC) over high-speed communication networks BIB001 . The advanced metering infrastructure (AMI) systems with millions of smart meters in the distribution systems provide innovative two-way, real-time (RT) communications in the smart grid, which promote numerous benefits from demand response, energy management, and consumer engagement. In addition, the increasing presence of energy storage, electrical vehicles, and other emerging techniques are consistently introducing new changes to the generation, transmission, and distribution of electricity. The information, computation, and communication systems in smart grid have instituted a ubiquitous cyber infrastructure interwoven with the PSs. Measurements and commands are constantly generated and transmitted between cyber and PSs. The measurements from the PSs are primarily composed of status data and analogue data: the status data contain the topological connectivity of power grid components; the analogue data are measurements of the system dynamics. On the basis of the measurements, operators determine the optimal control policies and issue the control commands to coordinate actuators in the PSs. In the presence of a fault or disturbance, diagnostic logs are recorded by supplementary recording devices to support the location, evaluation, mitigation, and restorations during emergencies. Sensor measurements are processed by centralised and distributed computation devices deployed at different levels and locations in the smart grid. In the traditional centralised operations, critical computations in EMS, including the state estimation (SE), optimal power flow (OPF), economic dispatch (ED), and automatic generation control (AGC), among others, are hosted in the control centres. In pursuit of better efficiency, resiliency, and flexibility, latest developments in intelligent electronic devices and programmable logic circuits have increased the utilisation of distributed and localised computations in the smart grid. Communications in the smart grid have been primarily hosted on proprietary SCADA systems and networks. Industrial protocols such as IEC 61850 and DNP3 have been developed for communications between and within control centres and substations. New communication standards are being introduced in the smart grid to accommodate the integration of renewable energies, energy storage, and PMUs. Meanwhile, with the increasing efficiency requirements and cost pressures, the smart grid also increasingly relies on public communication infrastructures. Industrial control systems are accessing the Internet via ICT interfaces. Two-way communications between service providers and customers are also widely established through the AMI system, allowing flexible demand response for reliability and economic benefits.