ONLINE MONITORING OF POWER SYSTEM DYNAMICS BY PHASOR MEASUREMENTS AT LOW VOLTAGE TERMINALS

摘要

Wide area measurement system has been expected to be an important infrastructure to develop an advanced power system, which can be called a smart grid. It can monitor a large-scale interconnected power system by collecting data from distributed Phasor Measurement Units (PMUs), which can correct voltage phasors as sequential data with precise time synchronization. Today, the PMU can be available for not only power system operators but also every customer because it monitors low voltage terminals. In the circumstances, the wide area measurement system based on low voltage terminals can provide chances to observe a whole power system by online. Authors and co-researchers have developed some global monitoring networks in Japan and Southeast Asian countries. Sequential voltage phasors are measured at an outlet on the wall by the PMUs and they are collected on a data server through a general information network. This paper deals with an online monitoring system which is only plotting the data on a plane of frequency versus phase difference. The method is quite simple but it has been revealed that the data clusters on the plane imply power system behaviours. This paper especially emphasizes variations of data norms on the plane. In case of global phenomena caused by a large disturbance, the data norm shows peculiar variations as compared with a case by a small local disturbance. As the data norm is a scalar quantity, continuous calculation of the data norm can be utilized as an event trigger. This paper discusses the data norm and its behaviour based on actual measurements.