Abstract:Ultra high voltage ( UHV) AC transmission system plays an important role in the long-distance, large-capacity transmission of electric energy in China. However, the phenomenon of bus power imbalance often occurs in UHV AC transmission systems, especially in substations with series compensation devices. The paper analyzes in detail the causes of power calculation errors in UHV AC transmission lines after the installation of series compensation devices, derives the corresponding correction algorithm, and verifies the practical application effect of the algorithm by taking a substation in the west as an example. The problem of bus power imbalance is solved, and theoretical and methodological support is provided for the engineering practice of UHV substations. The conclusion is that the correction method based on Kirchhoff's law can accurately calculate the actual active and reactive power of the line.