Grounding Distance Protection Algorithm for Long Transmission Line Based on Parameter Identification

The long transmission line compensation algorithm using the traditional distance protection ranging equation will cause overreach when high resistance grounding faults happen in the end of protection domain.To solve this problem,we put forward a grounding distance protection algorithm for long transmission line based on parameter identification in time domain.When faults happen,the algorithm calculates the voltages and currents in the end of the line using the voltages and currents at the relay location,then calculates the fault distance in the end of the transmission line using a new differential equation,which is deduced with three unknown quantities and can be used in the long transmission line of distributing parameter characteristics.When the calculated fault distance is within the protection setting range,the fault happens inside the protection zone and the protection trips.Otherwise,no protection acts.Theoretical analysis and simulation results show that the proposed algorithm avoids the impacts from distribution capacitance current and fault transient signals,and has a high responding speed and high capacity of earth-fault resistance.This protection can trip reliably under 300 Ω earth-fault resistance in 300 km long transmission line without overreach.