Main Protection Scheme for UHV Transmission Lines

Based on the construction and operation characteristics of UHV transmission lines, the main protection scheme for UHV transmission lines was proposed in this paper. It is the cooperation of a pilot protection of negative sequence with directional comparison, a pilot protection of zero sequence with directional comparison and a segregated phase compensator type directional relay based on the fault component. In order to obtain the negative sequence component, this paper presents a new algorithm, in which the digital second order RC low-pass filter is combined with the half-wave differential discrete Fourier transform. By using microprocessor, the negative sequence directional element and the zero sequence directional element can be realized, which can operate within several milliseconds after fault inception. Both directional elements can also operate during asymmetrical beginning period of three phase fault. By taking advantage of the superiority of this algorithm, this main protection scheme proposed can operate quickly during faults.