Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> We describe new analytical techniques to help mitigate the disruptions to electric power grids caused by terrorist attacks. New bilevel mathematical models and algorithms identify critical system components (e.g., transmission lines, generators, transformers) by creating maximally disruptive attack plans for terrorists assumed to have limited offensive resources. We report results for standard reliability test networks to show that the techniques identify critical components with modest computational effort. <s> BIB001 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> This paper presents a solution procedure for the mixed-integer bilevel programming model of the electric grid security under disruptive threat problem, here concisely denoted by (ST-MIBLP), that was recently reported. Using results from linear programming theory and some basic linearization of products of binary-binary or binary-continuous variables, we recast (ST-MIBLP) into a standard (one-level) mixed-integer linear program (ST-MILP) with no more binary variables than in the original (ST-MIBLP). This transformation provides a framework for globally solving (ST-MIBLP) using available mixed-integer linear programming solvers. Some numerical results obtained by the new method are compared with those recently published, based on IEEE Reliability Test Systems. <s> BIB002 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> This paper generalizes the "terrorist threat problem" first defined by Salmero/spl acute/n, Wood, and Baldick by formulating it as a bilevel programming problem. Specifically, the bilevel model allows one to define different objective functions for the terrorist and the system operator as well as permitting the imposition of constraints on the outer optimization that are functions of both the inner and outer variables. This degree of flexibility is not possible through existing max-min models. The bilevel formulation is investigated through a problem in which the goal of the destructive agent is to minimize the number of power system components that must be destroyed in order to cause a loss of load greater than or equal to a specified level. This goal is tempered by the logical assumption that, following a deliberate outage, the system operator will implement all feasible corrective actions to minimize the level of system load shed. The resulting nonlinear mixed-integer bilevel programming formulation is transformed into an equivalent single-level mixed-integer linear program by replacing the inner optimization by its Karush-Kuhn-Tucker optimality conditions and converting a number of nonlinearities to linear equivalents using some well-known integer algebra results. The equivalent formulation has been tested on two case studies, including the 24-bus IEEE Reliability Test System, through the use of commercially available software. <s> BIB003 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> Abstract Previous methods for assessing the vulnerability of complex systems to intentional attacks or interdiction have either not been adequate to deal with systems in which flow readjusts dynamically (such as electricity transmission systems), or have been complex and computationally difficult. We propose a relatively simple, inexpensive, and practical method (“Max Line”) for identifying promising interdiction strategies in such systems. The method is based on a greedy algorithm in which, at each iteration, the transmission line with the highest load is interdicted. We apply this method to sample electrical transmission systems from the Reliability Test System developed by the Institute of Electrical and Electronics Engineers, and compare our method and results with those of other proposed approaches for vulnerability assessment. We also study the effectiveness of protecting those transmission lines identified as promising candidates for interdiction. These comparisons shed light on the relative merits of the various vulnerability assessment methods, as well as providing insights that can help to guide the allocation of scarce resources for defensive investment. <s> BIB004 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> We show how concepts from game theory can be used to find and evaluate strategies for defending an electric power system against antagonistic attacks. Consequently, the interaction between the antagonist and the defender of the system is envisaged as a game. In a numerical example, we study the performance of different defense strategies against a number of attack scenarios. Particularly, we study whether there is a dominant defense strategy and an optimal allocation of resources between protection of components and recovery <s> BIB005 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> This paper generalizes Benders decomposition to maximize a nonconcave objective function and uses that decomposition to solve an ldquoelectric power grid interdiction problem.rdquo Under one empirically verified assumption, the solution to this bilevel optimization problem identifies a set of components, limited by cardinality or ldquointerdiction resource,rdquo whose destruction maximizes economic losses to customers (and can thereby guide defensive measures). The decomposition subproblem typically incorporates a set of DC optimal power-flow models that cover various states of repair after an attack, along with a load-duration curve. Test problems describe a regional power grid in the United States with approximately 5000 buses, 6000 lines, and 500 generators. Solution time on a 2-GHz personal computer is approximately one hour. <s> BIB006 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> The vulnerability analysis is vital for safely running power grids. The simultaneous attack, which applies multiple failures simultaneously, does not consider the time domain in applying failures, and is limited to find unknown vulnerabilities of power grid networks. In this paper, we discover a new attack scenario, called the sequential attack, in which the failures of multiple network components (i.e., links/nodes) occur at different time. The sequence of such failures can be carefully arranged by attackers in order to maximize attack performances. This attack scenario leads to a new angle to analyze and discover vulnerabilities of grid networks. The IEEE 39 bus system is adopted as test benchmark to compare the proposed attack scenario with the existing simultaneous attack scenario. New vulnerabilities are found. For example, the sequential failure of two links, e.g., links 26 and 39 in the test benchmark, can cause 80% power loss, whereas the simultaneous failure of them causes less than 10% power loss. In addition, the sequential attack is demonstrated to be statistically stronger than the simultaneous attack. Finally, several metrics are compared and discussed in terms of whether they can be used to sharply reduce the search space for identifying strong sequential attacks. <s> BIB007 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> Recently, the sequential attack, where multiple malignant contingencies are launched by attackers sequentially, has revealed power grid vulnerability under cascading failures. This paper systematically analyzes properties and features of N-k cascaded- based sequential line-switching attacks using a DC power flow based cascading failure simulator (DC- CFS). This paper first explains the key factors behind cascade-based attacks, then compares three adopted metrics with an original line-margin metric to compute vulnerability indexes and design sequential attacks. Two target search schemes, i.e., offline and online target search in sequential attacks, are also presented. Simulation results of N-2 to N-4 line-switching attacks have suggested that the proposed line margin metric produces stronger sequential attacks, and online target search is more effective than offline search. Reasons behind counter-intuitive load loss resulting from different metrics are also analyzed to facilitate future study on the risk of sequential attacks. <s> BIB008 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> The modern society increasingly relies on electrical service, which also brings risks of catastrophic consequences, e.g., large-scale blackouts. In the current literature, researchers reveal the vulnerability of power grids under the assumption that substations/transmission lines are removed or attacked synchronously. In reality, however, it is highly possible that such removals can be conducted sequentially. Motivated by this idea, we discover a new attack scenario, called the sequential attack, which assumes that substations/transmission lines can be removed sequentially, not synchronously. In particular, we find that the sequential attack can discover many combinations of substation whose failures can cause large blackout size. Previously, these combinations are ignored by the synchronous attack. In addition, we propose a new metric, called the sequential attack graph (SAG), and a practical attack strategy based on SAG. In simulations, we adopt three test benchmarks and five comparison schemes. Referring to simulation results and complexity analysis, we find that the proposed scheme has strong performance and low complexity. <s> BIB009 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> By exploiting the vulnerabilities in cyber components, an attacker could intrude in the wind farm supervisory control and data acquisition (SCADA) system and energy management system (EMS), and maliciously trip one or multiple wind turbines. The reliability of the overall power system could thus be impacted by the performance of wind farms. In this paper, cyber attack scenarios concerning cyber components or networks are considered in the integrated wind farm SCADA/EMS system architecture. Two Bayesian attack graph models are adopted to represent the procedures of successful cyber attacks, and a mean time-to-compromise model is used by considering different attack levels and various vulnerabilities. Frequencies of successful cyber attacks on the wind farm SCADA/EMS system are estimated. A procedure for evaluating the power system reliability is proposed by considering wind turbine trips caused by various cyber attacks. Simulations are conducted based on a typical IEEE reliability test system. Simulation results indicate that the overall system reliability decreases when the frequency of successful attacks on the wind farm SCADA/EMS system and skill levels of attackers increase. <s> BIB010 </s> Cyber-physical attacks and defences in the smart grid: a survey <s> Interdiction attacks: <s> Recent studies on sequential attack schemes revealed new smart grid vulnerability that can be exploited by attacks on the network topology. Traditional power systems contingency analysis needs to be expanded to handle the complex risk of cyber-physical attacks. To analyze the transmission grid vulnerability under sequential topology attacks, this paper proposes a Q-learning-based approach to identify critical attack sequences with consideration of physical system behaviors. A realistic power flow cascading outage model is used to simulate the system behavior, where attacker can use the Q-learning to improve the damage of sequential topology attack toward system failures with the least attack efforts. Case studies based on three IEEE test systems have demonstrated the learning ability and effectiveness of Q-learning-based vulnerability analysis. <s> BIB011
The interdiction analysis is among the earliest investigations of power transmission system vulnerability under large-scale malicious attacks BIB001 . An interdiction refers to the tripping of lines, transformers, generators, buses, and/or substations in the transmission grid. In practise, the interdiction can be conducted directly by manipulated control commands or indirectly by false measurements. On the basis of a steady-state model, a bi-level max-min optimisation problem for the interdiction analysis has been formulated as where an attacker leverages the interdiction to maximise the system operator's minimal costs of operation and load shedding. g(P, d) are the OPF constraint functions with an upper-bound vector b, c is a vector of linearised cost factors, and P are the power system dynamics subjected to physical constraints. The inner minimisation solves an OPF problem in normal operations, and the outer maximisation solves the optimal interdiction as a binary vector d in the complete interdiction set D. The solutions can be obtained by mixed-integer bi-level programming BIB002 BIB003 , greedy search BIB004 , game theory BIB005 , and generalised Benders decomposition BIB006 . An interdiction scheme targeting wind farms in the smart grid through vulnerabilities the SCADA/EMS system has been recently proposed BIB010 . While interdiction has been modelled as multiple concurrent tripping in the above investigations, sequential attack schemes have revealed the risks of blackout resulting from multi-line interdiction BIB007 BIB008 . As the timing and order of interdiction are non-trivial challenges to the formulation of an optimisation problem BIB007 BIB008 , data-driven approach based on reinforcement learning BIB011 and heuristic approach based on risk graph BIB009 have been proposed to search for the critical attack sequence. Both sequential schemes have identified effective schemes to exploit the cascading failure vulnerability that leads to massive blackouts.