Inter-area oscillations: Identifying causes of poor damping using phasor measurement units

Inter-area oscillations involve wide areas of the power grid and numerous power system components. Therefore, identifying the components influencing negatively the oscillations damping is extremely challenging. The method proposed in this paper analyzes some variables monitored by phasor measurement units (PMU) in order to have a better understanding of the oscillation behavior. The influence of the following parameters is studied: the topology, the load model, power flows or the presence of fast exciters. The method works by clustering the mode frequency, the voltage angle difference between areas and the mode shapes. All of these variables can be given by PMUs. Starting from a sufficiently damped power system, the proposed clustering determines the main cause of a damping decrease. The weaknesses of the power system can then be emphasized to help the operators to take the appropriate actions to reinforce their system. The method is illustrated on a 4-machine test system.