Automated test system to assess reporting latency in PMUs

The accuracy of the measurements provided by a Phasor Measurement Unit (PMU), such as phasor amplitude and phase angle, frequency and rate of change of frequency (ROCOF), can be very high. Nevertheless, other factors should be considered for a proper employment of the measurement devices. In particular, sufficiently low reporting latency should be guaranteed, to ensure that the PMU measurements are made available in a fair time. Many internal and external factors affect the overall latency of the output data of a PMU connected to a phasor data concentrator (PDC). Among them, it is possible to mention the type of the measurement algorithm, the processing time and the delay due to the transmission and the communication channel. The Standard IEEE C37.118.1-2011 defines the latency pertaining directly to the PMU. This paper proposes a simple and fast method to evaluate the PMU reporting latency, considering a high number of messages at high reporting rates. The method is based on the statistic evaluation of the difference of two timestamps provided by two independent time sources. The methodology is implemented in a prototyping architecture based on a general purpose modular data acquisition platform. The characterization phase of the obtained test system is illustrated in details. The obtained results prove that the system is compliant with the definition, the observation interval and the accuracy required by the Standard IEEE C37.118.1, along with its amendment IEEE C37.118.1a. Then, the test system is used to investigate the performance of commercial PMUs with different settings. The most significant results of this study are also presented and discussed.