Factor of Security (FoS): Quantifying the Security Effectiveness of Redundant Smart Grid Subsystems

According to International Electrotechnical Commission (IEC) 61850-90-4, most smart grid substations are designed with redundancy in order to improve their availability in case of failures. Redundancy usually takes the form of having multiple subsystems with identical functionality based on the assumption that failures in one subsystem are isolated from other subsystems. However, this is not necessarily true in the case of failures caused by malicious attacks, because attackers can easily reuse their skills and tools across different subsystems under similar configurations. Taking this into consideration, this article introduces the factor of security (FoS) metrics to quantify the security effectiveness of redundant subsystems in smart grids. Specifically, we first apply the attack graph model to capture various threats in smart grids and substations; we then formally define the FoS metric and the probabilistic FoS metric, and finally we evaluate those metrics through simulations.

1 Introduction

By INTEGRATING information and communication technologies, smart grids could potentially enhance the efficiency and reliability of future power systems [1]. Such a capability grants smart grids an important role in addressing the global challenge that the demand for energy is growing faster than its supply [2]. On the other hand, the smart grid is a complex system involving many components for the generation, transmission, and distribution of energy to the end users. In particular, substations, which are responsible for protecting, monitoring and controlling the power system, represent one of the most critical components in a smart grid. This has been demonstrated in a study by the Federal Energy Regulatory Commission (FERC) which shows a coordinated attack on just nine substations (out of 55,000) can bring down the entire United States (US) power grid [3]. Also, in the real-world attack on the Ukrainian power grid, which resulted in a blackout affecting 225,000 customers and lasted for several hours [4], substations were also among the main targets.