Temporary Detuning of Cablified Transmission Grids for Mitigation of Resonant Overvoltages

Changes in the power system such as an increased use of cables in transmission systems lead to lower resonance frequencies, a possible consequence being an increased risk for resonant overvoltages. This paper presents a method for protecting the power system from resonant overvoltages caused by transformer energization or fault clearing in the vicinity of large transformers. The method utilizes disconnection of cables according to a predetermined scheme that shifts the system resonance in case the harmonic voltage exceeds a threshold. Compared to other available mitigation measures, the proposed method is inexpensive, robust, and acts only when needed, thereby minimizing any impact during normal operation. The method is exemplified using a realistic network model in PSCAD, showing that by employing the method it is possible to reduce the duration of the overvoltages, and thereby the stress on surge arresters and other equipment.