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This paper proposes a load transfer optimization (LTO) model involving hot-spot temperature (HST) and top-oil temperature (TOT) limits of transformers. This work aims to address the overload problem and transformer HST and TOT excursions via LTO. First, the equivalent thermal model for the HST and TOT of transformers under external cooling conditions are discussed, and then the corresponding linearized HST and TOT constraints with varied thermal resistances are derived using the discretization method. Moreover, the proposed LTO model is formulated on the reconfigurable topology of high voltage distribution networks (HVDNs) in China. This proposed LTO model can achieve the optimal network reconfiguration scheme subject to temperature limits and system operation constraints, with the least switching operation cost and the maximum margins of reactive power exchange between HVDNs and transmission systems. Finally, the effectiveness of the proposed LTO model is validated by the modified IEEE-14 node system and the practical HVDNs in China. [ABSTRACT FROM AUTHOR]

Calculation of geomagnetically induced current (GIC) flowing through power system during the geomagnetic storm has attracted more attention recently. However, for high voltage power systems with transmission lines over hundreds or even thousands of kilometers, the earth model and geomagnetical field generally vary significantly. So, it is essential to take them into consideration using limited earth survey sites and geomagnetic observatories. To address this problem, a Kriging method is introduced in this paper to make earth model and geomagnetical field interpolations. It has the characteristic of spatial autocorrelation by considering not only the distances between predicted points and training points but also the distances between training points themselves. Finally, a case study of the Central China 1000 kV ultra-high voltage (UHV) grid is carried out to illustrate the applicability and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]