Adaptive Distance Protection Of UHV/EHV Transmission Line

EHV/UHV transmission line plays an important role in strong smart grid; distance protection has got widespread application in high voltage transmission line relay protection due to its characteristics of being less affected by the system operation mode and grid structure. By analyzing fault signal characteristics in EHV/ UHV transmission line and studying on the mechanism of the emergence of steady-state overreach and transient overreach, this paper provides a new fault signal analysis algorithm and a new adaptive distance protection criterion.First, several distance protection algorithms are analyzed and compared. Considering the fault signal with slow decayed DC component and rich high frequency components in EHV/UHV transmission line distance protection, prony algorithm is adopted to fit fault signal. In order to reduce the impact of noise on prony algorithm, the order of prony algorithm is determined by Singular Value Decomposition(SVD) method, and SVD-prony algorithm is constructed.Second, in view of the steady-state physical characteristic in EHV and UHV transmission line, the reason why steady-state overreach occur is introduced exactly and the advantage of employing power frequency distance relays in solving steady-state overreach is penetrated. Based on analyzing several power frequency distance relays criterion, unified expression of power frequency distance relays is established. By studying on the relationship of the load change and protection area, an adaptive strategy is established to adjust protection area by changing the parameters, thus, it can avoid steady-state overreach at the end of transmission line.Third, considering the transient physical characteristics in EHV and UHV transmission line, the reason why transient overreach occur is introduced. By calculating the fitting error of SVD-prony, and according to the relationship between fitting error and the calculation reactance error, amending curve is constructed. According to the amending curves, the distance protection settings have been amended adaptively to avoid transient overreach, so it can make protection more quickly.An EHV and UHV power system are built using simulation tool ATP, from which we can get voltage and current signal in various fault conditions. Based on MatLab platform, the parameters of fault signals are estimated using SVD-prony algorithm, then, the adaptive criteria is validated. The simulation results show that SVD-prony algorithm and adaptive criterion used to solving steady-state overreach and transient overreach can adapt to the changes of the operational mode and fault state, therefore, it makes the performance of the distance protection in EHV and UHV transmission line better.