Monitoring System Based on Phasor Measurement Units with Variable Reporting Rates

Abstract

Classical Wide-Area Monitoring Systems (WAMS) are characterized by a hierarchical architecture composed of Phasor Measurement Units (PMUs) and different levels of Phasor Data Concentrators (PDCs). The WAMS, based on synchrophasor technology, was originally designed for transmission systems; nevertheless, with the development of the smart grid paradigm, the benefits of this technology are being extended to the distribution network. Normally, PMUs send measurement data at a high and constant reporting rate to guarantee the monitoring of dynamic events in an electric transmission network. However, the typical communication systems expected to be used by distribution system operators will be generally shared and/or public and, in this case, the bandwidth available among PMUs and PDCs, or among the PDCs and the control centre, is strictly dependent on the type of communication channel used and on the level of network traffic. In this context, a new transmission logic for the transfer of data between PMUs and PDCs, based on the knowledge of the ongoing conditions of the electric grid, can be implemented. The strategy proposed in this paper is to increase the measurement reporting rate only when the electric system changes from a steady-state condition to a dynamic and potentially unsafe one, without modifying the overall accuracy of the PMU measurement process. The risk of losing important information related to a dynamic event is mitigated by sending to the PDC, after the event detection, also measurements relating to pre-trigger time interval in a burst of data packets that allow an insight on the signal evolution.