Trustworthiness of PMU data in the presence of synchronization issues

The monitoring applications based on Wide Area Measurement Systems require a high level of synchronization for the time sources to give highly accurate synchronized measurements. The Phasor Measurement Units (PMUs) meet these requirements by providing the measurements obtained from the voltage and current signals with an absolute time reference referred to the Coordinated Universal Time, typically provided by Global Positioning System receivers. For a practical usability of the data provided by PMUs, the measurement results should be accompanied by a suitable information about their quality, so that the system operator can definitely rely on them. In this paper, the behavior of commercial PMUs under loss and restoration of the GPS signal is analyzed and discussed by means of experimental tests. The performance of the devices in terms of Total Vector Error are correlated with the time quality information sent by PMUs, according to the standard IEEE C37.118.2, together with the measurements during the transients corresponding to synchronization issues. The reported analysis allows putting in evidence important considerations about measurement accuracy and trustworthiness during synchronization issues and, in this perspective, highlights what are good practices in PMU implementation.