Monitoring amplitude, frequency and damping of power system oscillations with PMU measurements

Since 2005, Statnett (the Norwegian transmission system operator), ABB and Sintef Energy Research, have worked together on designing, implementing and deploying a Wide Area Monitoring System (WAMS) completely integrated with Statnettpsilas SCADA system. This paper focuses on the application for on-line monitoring of amplitude, frequency and damping of power oscillations as implemented in the WAMS.The power transfer capability in the Nordic transmission system is at times limited by the risk of instability due to inter- area power oscillations. With the WAMS in operation detailed operational data is available to alert operators and support identification of potentially unstable system conditions. In the past, such power swings would often go by unnoticed, and therefore this application can be of critical importance. WAMS recordings from a recent system disturbance leading to temporary sustained power oscillations are presented and used to discuss the ability to provide early detection of power oscillations in terms of amplitude, frequency and damping of the dominant mode. The main conclusion is that the system is able to identify accurately the amplitude and frequency of the main oscillatory modes. Identification of damping is difficult in an on-line application, particularly when the magnitude of the oscillations is similar to that of random load variations. The present measurements, however, show that as the magnitude of these oscillations increase, the indicator on damping also becomes more reliable.