Measurement of Synchrophasors with Stand Alone Merging Units: a Preliminary Study

Power grids must be more and more capable of adapting to a range of sometimes rapidly fluctuating conditions, originating by both fast variations of absorbed and generated power, especially from renewable sources. The implementation of substation automation is rapidly increasing, fostered by the 'digitalization' of the substations themselves. In this context, where voltage and current Instrument Transformers (ITs) have digital output or their output is digitized by the Stand Alone Merging Units (SAMUs), the natural evolution of a Phasor Measurement Unit is to become all-digital, that is not to have analog input but to process directly the Sampled Values (SVs) to extract the desired quantities. However, since these instruments can be used to implement critical tasks for the power system (stability control, remote diagnostics and so on) it is very important to assure the accuracy of the measurements. Therefore, this paper presents the results of a preliminary study where the performance of a PMU implemented using the SVs from a commercial SAMU are experimentally tested in various test conditions suggested or inspired by the international standards.