The pumped storage power plants (PSPPs) are a special power source with flexible operation modes and various functions, which more and more have been put into operation in recent years. Compared with the traditional plants, the main wiring structure is also different in the PSPPs. Several high-voltage cables of almost one kilometer in length are usually used to connect the ground switching station and the underground main transformers. There are some abnormal or damaged accidents of transformers and high voltage cables. In this paper, we found that the long high-voltage cable and the no-load transformer cause the oscillation in the process of de-energizing. A simulation model is built by ATP-EMTP software. The field measurement of the de-energizing waveform was used to verify the correctness of the ATP-EMTP model. The results show that the number of oscillations increased to more than 15 times with a 2000 m high-voltage cable.

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