GNSS Time Signal Spoofing Detector for Electrical Substations

Abstract

This paper introduces a novel method of GNSS spoofing detection with applications in electrical substations. Time sensitive applications in electricity substations, including Phasor Measurement Units (PMU) and Merging Units (MU), rely on Global Navigation Satellite Signals (GNSS), often GPS, for time transfer. Recently, sophisticated ‘spoofing’ attacks have become feasible due to the availability of low cost Software Defined Radio (SDR) systems. The proposed method uses multiple GNSS receive antennas placed in close proximity at the electricity substation, such that it is not possible for an attacker to target a unique spoofing signal towards each antenna. In a system employing three or more receive antennas, during a spoofing attack two or more of the GNSS receive antennas will return an estimated position in impossible locations. This is sufficient to raise alarm that time sensitive applications should use an alternative time source or holdover clock. The contributions of this paper include a detailed description of the proposed method, an experimental assessment of GNSS receiver and substation clock position estimation variance to establish the minimum separation required between receive antennas, and a validation of the method by experimental demonstration. A further benefit of the authors’ method is that it may be put into practice immediately using commercial-off-the-shelf (COTS) substation clock equipment.