Local-Measurement-Based High-Speed Protection for Half-Wavelength UHV Lines

The half-wavelength ultra-high-voltage transmission system is an alternative technique for bulk-power transmission over very long distances. However, the operations and fault-characteristics of such systems are extremely different from conventional ones. Therefore, there is an urgent need to propose a protection scheme that adapts to the characteristics of the half-wavelength line. Towards this end, a local-measurement-based approach is proposed. According to the frequency-dependent model of the half-wavelength line, this paper uses the wavelet transform to decompose the arrival of the aerial-modal surge into several frequency bands. To acquire better accuracy, a weighted average approach is employed to modify the surge arrival time in each frequency band. According to the surge arrival interval between the predefined low-frequency and high-frequency bands, all types of fault, except single-line-to-ground faults when the fault inception angle is at zero-crossings, can be identified in a very short time-window. Simulation results indicate that the proposed protection scheme has satisfactory performance against internal faults and is quite secure under external fault conditions. Using local measurement only, the reach of the proposed protection scheme is no less than 80% of the entire length of the line, and the resistive coverage is also sufficiently high for UHV transmission systems.