Blog #8
Phasor Measurement Unit for Monitoring Power Systems
Radu Plamanescu – CRE
PHASOR MEASUREMENT UNIT (PMU)
Phasor measurement units (PMUs) extract phasors (magnitude and phase angle) of the voltage and current signals in a power system, with all phase angles precisely referenced to a common time frame with the aid of the GPS. In addition to the phasor values, a PMU can estimate the frequency and the ROCOF of the measured signals. A PMU can be a stand-alone device or a functional unit within another physical unit such as power system digital fault recorder (DFR), protection relay,or a meter. The process of calculation of synchrophasors for a typical commercial PMU can be further anlyzed in [1]. The calculated phasors are combined to form positive sequence measurements, and time-tagged with the timing information.
PHASOR DATA CONCENTRATOR (PDC)
A PDC is a function that combines synchrophasor data from many PMUs into a single time synchronized data stream for further processing. The functions of the PDC include monitoring the healthiness of the overall measurement system, data handling, processing, and storage as well as integrated features for power systems applications such as protection, control, and monitoring. A PDC can exchange phasor data with PDCs at other locations within a connected system. By proper placement of PDC units, multiple layers of data concentration can be implemented within a synchrophasor data system
Architecture of a Synchrophasor networks
A typical architecture of a synchrophasor network is shown in the figure. PMUs produce synchronized measurements of the phasors, frequency, and the rate of change of frequency of the voltage and current signals, and output time stamped phasor data to a communication network using a standard format at a predefined reporting rate. PMUs are generally located in different substations of a power system. Time signals from the GPS are used to synchronize the phasor measurements to a common time base, as well as to time stamp the measurements. Synchrophasor measurements transmitted from PMUs at various locations of an interconnected power system are communicated to Phasor Data Concentrators (PDCs) over a wide area communication network. PDCs might be arranged in a hierarchical order. The role of a PDC is to collect, time align and send the synchrophasor data from PMUs to higher level PDCs. Data can be stored and use the time-aligned data for wide-area monitoring applications.
[1]. A. G. Phadke and J. S. Thorp, “HISTORY AND APPLICATIONS OF PHASOR MEASUREMENTS,” 2006 IEEE PES Power Systems Conference and Exposition, Atlanta, GA, 2006, pp. 331-335, doi: 10.1109/PSCE.2006.296328.
[2]. R. Plamanescu, M. Albu, S. Gheorghe, S. Bugnar, M. Coroiu, ” PMU Cloud-based Applications for Power Systems Insight”, 54th International Universities Power Engineering Conference (UPEC), Bucharest, Romania, 2019.
