An Accurate Offline Phasor Estimation Technique For Fault Location In Series Compensated Lines

With the increasing demand of electric power supply, the necessity to transmit more power has become the need of the hour. The excess power can be transferred by building new infrastructure (costly and time taking) or by using series compensation (relatively cheaper and faster alternative). Series compensation is a technique in which line inductance is compensated by placing a capacitor in series with the line. This helps in increasing the transmission capacity of the existing line. Series compensated lines face several challenges when it comes to protection and fault location. Current and voltage signals used by the protection and fault location algorithms, contain considerable sub-synchronous frequency components (SSFCs) which do not damp sufficiently within a typical fault clearing time of the line protection system. Presence of such SSFCs affects the accuracy of the available phasor estimation techniques which in turn impacts the accuracy of phasor-based fault location algorithms. In the presented research work (refer publication 1) a new offline Prony-DFT (Discrete Fourier Transform) based phasor estimation technique is introduced, which almost eliminates these SSFCs in addition to removal of noise, harmonics and decaying DC and results in more accurate phasor estimation for fault location in series compensated transmission lines. The idea is to estimate the transient signal using Prony analysis. The transient signal thus obtained is subtracted from the original fault current/voltage signal to obtain the fundamental signal. Conventional one-cycle DFT algorithm is then used to perform phasor estimation. The performance of the proposed technique is evaluated using an assumed theoretical signal and PSCAD/EMTDC simulation and results are compared with the available accepted techniques, namely, Direct-Prony analysis and the 4-cycle Discrete Fourier transform algorithm.