Detection techniques for data-level spoofing in GPS-based phasor measurement units

To face the ever growing demand of electricity, the smart power grid, which includes a variety of operational and energy measures, aims at providing safe and reliable power supply, effective use of renewable energy, and better efficiency of the overall power grid. Phasor Measurement Units (PMUs) are important components of the smart grid Wide Area Measurement Systems (WAMS). A PMU is a transducer that converts the three-phase analog voltage or current signals into synchronized phasor measurements, known as synchrophasors. Typically, PMUs utilize Global Positioning System (GPS) reference source to provide the required synchronization across the wide geographical areas. On the other hand, civil GPS receivers are vulnerable to a number of different attacks such as jamming and spoofing, which can lead to inaccurate PMU measurements and consequently compromise the state estimation in the electric power grid. In this paper, we propose two countermeasures against GPS spoofing attacks in PMUs. In particular, we utilize the fact that in GPS-based PMUs, unlike most of the GPS applications, the position of the PMU receivers are already fixed and known. Our first technique employs an algorithm that accurately predicts the number of theoretically visible GPS satellites from a given position on earth; if the GPS receiver detects satellites which should not be visible at the time, this signifies a spoofing attempt. The second technique is an anomaly-based detection method which assumes that the malicious errors in GPS time solution are unlikely to be consistent with the expected statistics of the typical receiver clock. The effectiveness of the proposed techniques are confirmed by simulations.