Determining the Inter-area Modes of the Power System Network using Circuit Analogy

Power system are continuously exposed to different kinds of disturbances. These disturbances could be small or severe in nature and may cause electromechanical oscillations into the system. Depending upon the frequency of the oscillations and generators impacted, these oscillations can be categorized as inter-area, intra-area, control, and torsional oscillations. Among these, low frequency inter-area oscillations are of the major concern. These low frequency oscillations can travel large distances. Frequency of these inter-area oscillations lies in the range of 0.1 to 0.7 Hz. If these disturbances are not adequately damped then it can impact the performance of generators resulting in problems of stability and poor power quality, and in worst cases may also result in loss of synchronism. Few state of the art methods to determine the inter-area modes include small signal stability analysis, prony analysis, online mode estimation techniques. However, the complexity to determine the inter-area modes using state of the art methods may increase with an increase in the size of the system and inclusion of power electronics devices. In this paper, we present a simple and intuitive method to determine the interarea modes of the power system using circuit analogy. Interarea modes of IEEE 3 machine 9 bus system is determined using the proposed approach and results are validated with the small signal results.