Interoperability of Phasor Measurement Units under Voltage Unbalance Conditions

The Phasor Measurement Unit (PMU) is a modern instrument that measures magnitude, phase angle, frequency and rate of change of frequency (ROCOF) from voltage and current signals in electric networks. It is designed to be used in the monitoring and control of electric transmission systems. For each measurement, the PMU assigns a timestamp from an accurate time source; in this way, it is possible to correlate in a common time axis all the measurements collected from different points of the electrical grid. Nowadays, the PMU is a key element of modern Wide Area Measurement Systems (WAMSs) and the number of devices installed in the field is increasing. To guarantee the interoperability of commercial PMUs from different vendors and models, the synchrophasor standard IEEE C37.118.1-2011 (along with its amendment and its predecessors) provides the tests and limits to verify compliance under different conditions. However, the standard does not cover all the conditions that might be encountered in the electric grid. In this work, in the context of a partnership between Terna and the University of Cagliari, the behavior of three different commercial PMUs compliant with three different versions of the synchrophasor standard will be analyzed to study the interoperability of PMUs under the unconventional (i.e. not considered as a mandatory test in current standards) condition of voltage unbalance.