The application of digital relay in fault location identification for cable in steel-pipe

The Electromagnetic Transients Program (EMTP) after minor adaptation is utilized to simulate the grounded fault of a cable in a steel-pipe. The zero sequence impedance became nonlinear during the fault period, because the zero sequence current in a steel-pipe induced a magnetic saturation effect. Consequently, the zone protection of a cable in a steel-pipe has a serious error if a traditional distance relay is used. To correct this possible malfunction a novel idea using the proposed digital relay is presented. The physical zero sequence impedance will dynamically be modified according to the zero sequence current in case of a grounded fault. With such real cable data, an accurate fault location of cable in a steel-pipe is accordingly estimated.