Risk of over frequency-overvoltage and its suppression strategies after the separation of small grid in remote areas from the main grid

With the construction of the power grids in the areas without electricity, the small power grids of remote areas, which are characterized by small hydroelectric generators and light load, are gradually connected with the main grids via the connecting lines. However, due to the remoteness, the connecting line between the small grid and the main network can often be hundreds of kilometers. Once these small grids are separated from the main grid because of failure, the excess active power in the isolated grids and the charging power of the long connecting lines may cause severe risks of over frequency and overvoltage in the isolated grids, which are worthy of attention and study. Firstly, taking the power grids of a certain Tibetan area integrated in Sichuan grid as the sample cases, this paper studies the phenomena and the mechanism of high frequency-high voltage risk after small grids separated from the main grids. Secondly, this paper discusses the influence of the control modes of the governors and excitation devices of generators on the risk of over frequency - overvoltage risk. Finally, based on the analysis of the drawbacks of the traditional suppression strategy, a novel strategy is proposed. Simulation results verified the effectiveness of the strategy.