Phasor Measurement Unit with Digital Inputs: Synchronization and Interoperability Issues

In recent years, electrical substations are experiencing a rapid transition toward a fully digital measurement infrastructure in terms of data acquisition, storage, and processing. The IEC Std 61850-9-2 defines the data format, also known as sampled value (SV), to be employed by instrument transformers, merging units, and controller devices. In this scenario, it is reasonable to expect that the phasor measurement units (PMUs) will be directly connected with digital instrument transformers and will be required to process directly the SV data stream. In this article, we present the design and development of a stand-alone PMU based on digital inputs. The prototype has been characterized in terms of estimation accuracy and enriched with a novel functionality that allows for monitoring the time quality of the SV data stream. In this way, the device truly becomes an intelligent electronic device (IED) that guarantees higher interoperability and a more robust management of sporadic synchronization issues. The proposed results confirm the potential of SV-based PMUs and highlight the possibility of further enhancement for synchrophasor measurements based on digital inputs only.