Mitigating the impacts of geomagnetic disturbances on the small signal stability

Geomagnetically induced currents (GICs) caused by geomagnetic disturbances (GMDs) flow through the transformers, which lead to the increase of reactive power loss (QGIC ). As reactive loads added to the system, QGIC causes the change of power flow distribution, which connects GMDs with small signal stability. Installing blocking devices (BDs) in the neutral points can reduce the negative effects on the grids. Obtaining the best effect is challenging, because the amplitude and direction of induced geoelectric fields (IGFs) are uncertain and non-stationary. Taking the credibility of damping ratio less than 0.05 as an index, the impact of GMDs on small signal stability is quantitatively evaluated. It is found that when intense GMDs occur, the risk of small signal instability increases significantly. Based on the voltage/damping ratio sensitivity joint feature space, the sensitivity scenario is obtained through scenario clustering. Moreover, upon optimal placement of BDs based on joint sensitivity (JS) scenarios, it is observed that the risk index can be significantly reduced compared to that in constant induced geoelectric fields (CIGF) and varying induced geoelectric fields (VIGF) scenarios.