Estimation of Area-Wise Effective Inertia of a Power System Using Energy Variations

Upon a disturbance, the frequency varies due to the power imbalance present in the power system. The frequency variation immediately after the disturbance is primarily determined by the inertia of the power system. However, the load response also plays a crucial role in determining the frequency response. Following a disturbance, the voltage and frequency of the power system vary depending on the nature of the disturbance. In effect, the load also varies due to its dependence on voltage and frequency. The variation in load, in addition to inertia, affects the frequency response immediately after the disturbance. Effective inertia may be defined as the sum of the system's actual inertia and the inertia-like impact of the load change on frequency response. This paper presents a methodology to estimate the area-wise effective inertia of a power system. The energy variations calculated from the power flow through the tie-lines are used to calculate the inertia. Thus, the calculated inertia represents the inertial response of large and distributed generators and the effect of load variation on frequency response. The paper also examines how, given the system's actual inertia, the effective inertia varies in response to various system factors. Using the IEEE-39 bus test system, the proposed method is illustrated.