Reliable Dynamic State Estimation Based Protection during Geomagnetic Disturbances

Geomagnetic disturbances (GMD) occur when intensive solar wind interacts with Earth's magnetic field. During this interaction, the geographically extensive power system is impacted by the geomagnetically induced current (GIC), which is a pseudo-DC current (0.0001 Hz to 1 Hz). GIC causes half cycle saturation of iron core circuits and subsequent distortion of current and voltage waveforms, resulting in overheating transformers and increasing reactive power consumption. In addition, the distorted waveforms may lead to substantial harmonics in measurements. As many protective relays respond drastically different under the influence of different orders of harmonics, these distorted measurements may risk the operation of protective relays. Moreover, GMD introduces DC flux in iron cores of instrumentation transformers, leading to gross distortion in measurements, which further reduces the reliability of relays. Therefore, a protective scheme with reliable performance in the presence of GMD is needed. Dynamic state estimation (DSE) based protection utilizes a high-fidelity model of the protection zone, a set of measurements from merging units, and a DSE algorithm to give the best estimates of the states of the protection zone. In this paper, we analyze the performance of the DSE based protection relays considering harmonics during GMD. The reliability of the relays is examined under different fault scenarios of transformers and capacitor banks, compared against conventional protection scheme. The simulation results show that during GMD, mis-operation is observed in conventional protection schemes, while the DSE based protection remains reliable.