Long transmission line distance protection based on parameter identification in time domain

The traditional distance protections applied to the long transmission line have transient overreach problem caused by influence of line distribution capacitance, so a new time-domain distance protection method with parameter identification is proposed in the paper. With distributed parameter line model, the setting-point voltage and current of the protection are calculated in accordance with voltage and current measured in local terminal, and then distance protection algorithm of differential equation is used to distinguish internal fault from external fault. In addition, using linear interpolation, voltage and current distribution along the line can be calculated by data obtained with a low frequency sampling. Simulation results show that the scheme can distinguish internal fault from external fault correctly and avoid the transient overreach effectively. It needs low sampling frequency and is not affected by line distribution capacitance current and non-periodic component, so the reliability of distance protection is higher than ever. This work is supported by National Natural Science Foundation of China (No. 50677051, No. 50677061), Specialized Research Fund for the Doctoral Program of Higher Education (No. 20070698057).