A Multi-Layered, Multi-Receiver Architecture

N O V E M B E R / D E C E M B E R 2 0 1 4 www.insidegnss.com Efficient power transmission and distribution would benefit from synchronized near–real-time measurements of voltage and current phasors at widely dispersed locations in an electric power grid. Such measurements also could enable effective realtime system monitoring and control, which are considered to be the key to preventing wide-scale cascading outages like the 2003 Northeast Blackout. A phasor measurement unit (PMU), also known as a synchrophasor, is a device capable of measuring power system voltage and current phasors at a rate of thousands of samples per second. The samples are time-stamped with one-microsecond or better accuracy to a common absolute time reference provided by the GPS receivers attached to PMUs. Unfortunately, low-received-power, unencrypted civil GPS signals have proven to be vulnerable to jamming and spoofing attacks. A jammer emits a high-power interfering signal at the GPS frequency in order to deny nearby GPS receivers access to the GPS signal. A spoofer broadcasts a counterfeit GPS signal that overpowers the authentic signal so as to manipulate a victim receiver’s reported position, time, or both. In a future scenario where PMU data play a significant role in power system operations, an attacker might Synchronized voltage and current phasor measurements provided by phasor measurement units (PMUs) can potentially augment power system monitoring, control, and protection functions. PMUs use GPS receivers to synchronize measurements across a wide geographical area. However, GPS signals are vulnerable to jamming, spoofing, and accidental receiver malfunctions. The authors present a multi-layered multireceiver architecture that hardens GPS-based timing against these hazards. The article describes eight countermeasures that address five known threat models and an experiment to test the viability of this approach. Analysis demonstrates high reliability and robustness for the new architecture. GPS-BASED TIMING